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   (a) The FSF's Front-Cover Text is:

   A GNU Manual

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   You have freedom to copy and modify this GNU Manual, like GNU
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INFO-DIR-SECTION GNU Libraries
START-INFO-DIR-ENTRY
* libgomp: (libgomp).          GNU Offloading and Multi Processing Runtime Library.
END-INFO-DIR-ENTRY

   This manual documents libgomp, the GNU Offloading and Multi
Processing Runtime library.  This is the GNU implementation of the
OpenMP and OpenACC APIs for parallel and accelerator programming in
C/C++ and Fortran.

   Published by the Free Software Foundation 51 Franklin Street, Fifth
Floor Boston, MA 02110-1301 USA

   Copyright (C) 2006-2019 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover texts
being (a) (see below), and with the Back-Cover Texts being (b) (see
below).  A copy of the license is included in the section entitled "GNU
Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.


File: libgomp.info,  Node: Top,  Next: Enabling OpenMP,  Up: (dir)

Introduction
************

This manual documents the usage of libgomp, the GNU Offloading and
Multi Processing Runtime Library.  This includes the GNU implementation
of the OpenMP (https://www.openmp.org) Application Programming
Interface (API) for multi-platform shared-memory parallel programming
in C/C++ and Fortran, and the GNU implementation of the OpenACC
(https://www.openacc.org) Application Programming Interface (API) for
offloading of code to accelerator devices in C/C++ and Fortran.

   Originally, libgomp implemented the GNU OpenMP Runtime Library.
Based on this, support for OpenACC and offloading (both OpenACC and
OpenMP 4's target construct) has been added later on, and the library's
name changed to GNU Offloading and Multi Processing Runtime Library.

* Menu:

* Enabling OpenMP::            How to enable OpenMP for your applications.
* OpenMP Runtime Library Routines: Runtime Library Routines.
                               The OpenMP runtime application programming
                               interface.
* OpenMP Environment Variables: Environment Variables.
                               Influencing OpenMP runtime behavior with
                               environment variables.
* Enabling OpenACC::           How to enable OpenACC for your
                               applications.
* OpenACC Runtime Library Routines:: The OpenACC runtime application
                               programming interface.
* OpenACC Environment Variables:: Influencing OpenACC runtime behavior with
                               environment variables.
* CUDA Streams Usage::         Notes on the implementation of
                               asynchronous operations.
* OpenACC Library Interoperability:: OpenACC library interoperability with the
                               NVIDIA CUBLAS library.
* The libgomp ABI::            Notes on the external ABI presented by libgomp.
* Reporting Bugs::             How to report bugs in the GNU Offloading and
                               Multi Processing Runtime Library.
* Copying::                    GNU general public license says
                               how you can copy and share libgomp.
* GNU Free Documentation License::
                               How you can copy and share this manual.
* Funding::                    How to help assure continued work for free
                               software.
* Library Index::              Index of this documentation.


File: libgomp.info,  Node: Enabling OpenMP,  Next: Runtime Library Routines,  Prev: Top,  Up: Top

1 Enabling OpenMP
*****************

To activate the OpenMP extensions for C/C++ and Fortran, the
compile-time flag `-fopenmp' must be specified.  This enables the
OpenMP directive `#pragma omp' in C/C++ and `!$omp' directives in free
form, `c$omp', `*$omp' and `!$omp' directives in fixed form, `!$'
conditional compilation sentinels in free form and `c$', `*$' and `!$'
sentinels in fixed form, for Fortran.  The flag also arranges for
automatic linking of the OpenMP runtime library (*note Runtime Library
Routines::).

   A complete description of all OpenMP directives accepted may be
found in the OpenMP Application Program Interface
(https://www.openmp.org) manual, version 4.5.


File: libgomp.info,  Node: Runtime Library Routines,  Next: Environment Variables,  Prev: Enabling OpenMP,  Up: Top

2 OpenMP Runtime Library Routines
*********************************

The runtime routines described here are defined by Section 3 of the
OpenMP specification in version 4.5.  The routines are structured in
following three parts:

* Menu:

Control threads, processors and the parallel environment.  They have C
linkage, and do not throw exceptions.

* omp_get_active_level::        Number of active parallel regions
* omp_get_ancestor_thread_num:: Ancestor thread ID
* omp_get_cancellation::        Whether cancellation support is enabled
* omp_get_default_device::      Get the default device for target regions
* omp_get_dynamic::             Dynamic teams setting
* omp_get_level::               Number of parallel regions
* omp_get_max_active_levels::   Maximum number of active regions
* omp_get_max_task_priority::   Maximum task priority value that can be set
* omp_get_max_threads::         Maximum number of threads of parallel region
* omp_get_nested::              Nested parallel regions
* omp_get_num_devices::         Number of target devices
* omp_get_num_procs::           Number of processors online
* omp_get_num_teams::           Number of teams
* omp_get_num_threads::         Size of the active team
* omp_get_proc_bind::           Whether theads may be moved between CPUs
* omp_get_schedule::            Obtain the runtime scheduling method
* omp_get_team_num::            Get team number
* omp_get_team_size::           Number of threads in a team
* omp_get_thread_limit::        Maximum number of threads
* omp_get_thread_num::          Current thread ID
* omp_in_parallel::             Whether a parallel region is active
* omp_in_final::                Whether in final or included task region
* omp_is_initial_device::       Whether executing on the host device
* omp_set_default_device::      Set the default device for target regions
* omp_set_dynamic::             Enable/disable dynamic teams
* omp_set_max_active_levels::   Limits the number of active parallel regions
* omp_set_nested::              Enable/disable nested parallel regions
* omp_set_num_threads::         Set upper team size limit
* omp_set_schedule::            Set the runtime scheduling method

Initialize, set, test, unset and destroy simple and nested locks.

* omp_init_lock::            Initialize simple lock
* omp_set_lock::             Wait for and set simple lock
* omp_test_lock::            Test and set simple lock if available
* omp_unset_lock::           Unset simple lock
* omp_destroy_lock::         Destroy simple lock
* omp_init_nest_lock::       Initialize nested lock
* omp_set_nest_lock::        Wait for and set simple lock
* omp_test_nest_lock::       Test and set nested lock if available
* omp_unset_nest_lock::      Unset nested lock
* omp_destroy_nest_lock::    Destroy nested lock

Portable, thread-based, wall clock timer.

* omp_get_wtick::            Get timer precision.
* omp_get_wtime::            Elapsed wall clock time.


File: libgomp.info,  Node: omp_get_active_level,  Next: omp_get_ancestor_thread_num,  Up: Runtime Library Routines

2.1 `omp_get_active_level' - Number of parallel regions
=======================================================

_Description_:
     This function returns the nesting level for the active parallel
     blocks, which enclose the calling call.

_C/C++_
     _Prototype_:  `int omp_get_active_level(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_active_level()'

_See also_:
     *note omp_get_level::, *note omp_get_max_active_levels::, *note
     omp_set_max_active_levels::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.20.


File: libgomp.info,  Node: omp_get_ancestor_thread_num,  Next: omp_get_cancellation,  Prev: omp_get_active_level,  Up: Runtime Library Routines

2.2 `omp_get_ancestor_thread_num' - Ancestor thread ID
======================================================

_Description_:
     This function returns the thread identification number for the
     given nesting level of the current thread.  For values of LEVEL
     outside zero to `omp_get_level' -1 is returned; if LEVEL is
     `omp_get_level' the result is identical to `omp_get_thread_num'.

_C/C++_
     _Prototype_:  `int omp_get_ancestor_thread_num(int level);'

_Fortran_:
     _Interface_:  `integer function omp_get_ancestor_thread_num(level)'
                   `integer level'

_See also_:
     *note omp_get_level::, *note omp_get_thread_num::, *note
     omp_get_team_size::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.18.


File: libgomp.info,  Node: omp_get_cancellation,  Next: omp_get_default_device,  Prev: omp_get_ancestor_thread_num,  Up: Runtime Library Routines

2.3 `omp_get_cancellation' - Whether cancellation support is enabled
====================================================================

_Description_:
     This function returns `true' if cancellation is activated, `false'
     otherwise.  Here, `true' and `false' represent their
     language-specific counterparts.  Unless `OMP_CANCELLATION' is set
     true, cancellations are deactivated.

_C/C++_:
     _Prototype_:  `int omp_get_cancellation(void);'

_Fortran_:
     _Interface_:  `logical function omp_get_cancellation()'

_See also_:
     *note OMP_CANCELLATION::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.9.


File: libgomp.info,  Node: omp_get_default_device,  Next: omp_get_dynamic,  Prev: omp_get_cancellation,  Up: Runtime Library Routines

2.4 `omp_get_default_device' - Get the default device for target regions
========================================================================

_Description_:
     Get the default device for target regions without device clause.

_C/C++_:
     _Prototype_:  `int omp_get_default_device(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_default_device()'

_See also_:
     *note OMP_DEFAULT_DEVICE::, *note omp_set_default_device::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.30.


File: libgomp.info,  Node: omp_get_dynamic,  Next: omp_get_level,  Prev: omp_get_default_device,  Up: Runtime Library Routines

2.5 `omp_get_dynamic' - Dynamic teams setting
=============================================

_Description_:
     This function returns `true' if enabled, `false' otherwise.  Here,
     `true' and `false' represent their language-specific counterparts.

     The dynamic team setting may be initialized at startup by the
     `OMP_DYNAMIC' environment variable or at runtime using
     `omp_set_dynamic'.  If undefined, dynamic adjustment is disabled
     by default.

_C/C++_:
     _Prototype_:  `int omp_get_dynamic(void);'

_Fortran_:
     _Interface_:  `logical function omp_get_dynamic()'

_See also_:
     *note omp_set_dynamic::, *note OMP_DYNAMIC::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.8.


File: libgomp.info,  Node: omp_get_level,  Next: omp_get_max_active_levels,  Prev: omp_get_dynamic,  Up: Runtime Library Routines

2.6 `omp_get_level' - Obtain the current nesting level
======================================================

_Description_:
     This function returns the nesting level for the parallel blocks,
     which enclose the calling call.

_C/C++_
     _Prototype_:  `int omp_get_level(void);'

_Fortran_:
     _Interface_:  `integer function omp_level()'

_See also_:
     *note omp_get_active_level::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.17.


File: libgomp.info,  Node: omp_get_max_active_levels,  Next: omp_get_max_task_priority,  Prev: omp_get_level,  Up: Runtime Library Routines

2.7 `omp_get_max_active_levels' - Maximum number of active regions
==================================================================

_Description_:
     This function obtains the maximum allowed number of nested, active
     parallel regions.

_C/C++_
     _Prototype_:  `int omp_get_max_active_levels(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_max_active_levels()'

_See also_:
     *note omp_set_max_active_levels::, *note omp_get_active_level::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.16.


File: libgomp.info,  Node: omp_get_max_task_priority,  Next: omp_get_max_threads,  Prev: omp_get_max_active_levels,  Up: Runtime Library Routines

2.8 `omp_get_max_task_priority' - Maximum priority value
========================================================

that can be set for tasks.
_Description_:
     This function obtains the maximum allowed priority number for
     tasks.

_C/C++_
     _Prototype_:  `int omp_get_max_task_priority(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_max_task_priority()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.29.


File: libgomp.info,  Node: omp_get_max_threads,  Next: omp_get_nested,  Prev: omp_get_max_task_priority,  Up: Runtime Library Routines

2.9 `omp_get_max_threads' - Maximum number of threads of parallel region
========================================================================

_Description_:
     Return the maximum number of threads used for the current parallel
     region that does not use the clause `num_threads'.

_C/C++_:
     _Prototype_:  `int omp_get_max_threads(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_max_threads()'

_See also_:
     *note omp_set_num_threads::, *note omp_set_dynamic::, *note
     omp_get_thread_limit::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.3.


File: libgomp.info,  Node: omp_get_nested,  Next: omp_get_num_devices,  Prev: omp_get_max_threads,  Up: Runtime Library Routines

2.10 `omp_get_nested' - Nested parallel regions
===============================================

_Description_:
     This function returns `true' if nested parallel regions are
     enabled, `false' otherwise.  Here, `true' and `false' represent
     their language-specific counterparts.

     Nested parallel regions may be initialized at startup by the
     `OMP_NESTED' environment variable or at runtime using
     `omp_set_nested'.  If undefined, nested parallel regions are
     disabled by default.

_C/C++_:
     _Prototype_:  `int omp_get_nested(void);'

_Fortran_:
     _Interface_:  `logical function omp_get_nested()'

_See also_:
     *note omp_set_nested::, *note OMP_NESTED::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.11.


File: libgomp.info,  Node: omp_get_num_devices,  Next: omp_get_num_procs,  Prev: omp_get_nested,  Up: Runtime Library Routines

2.11 `omp_get_num_devices' - Number of target devices
=====================================================

_Description_:
     Returns the number of target devices.

_C/C++_:
     _Prototype_:  `int omp_get_num_devices(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_num_devices()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.31.


File: libgomp.info,  Node: omp_get_num_procs,  Next: omp_get_num_teams,  Prev: omp_get_num_devices,  Up: Runtime Library Routines

2.12 `omp_get_num_procs' - Number of processors online
======================================================

_Description_:
     Returns the number of processors online on that device.

_C/C++_:
     _Prototype_:  `int omp_get_num_procs(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_num_procs()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.5.


File: libgomp.info,  Node: omp_get_num_teams,  Next: omp_get_num_threads,  Prev: omp_get_num_procs,  Up: Runtime Library Routines

2.13 `omp_get_num_teams' - Number of teams
==========================================

_Description_:
     Returns the number of teams in the current team region.

_C/C++_:
     _Prototype_:  `int omp_get_num_teams(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_num_teams()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.32.


File: libgomp.info,  Node: omp_get_num_threads,  Next: omp_get_proc_bind,  Prev: omp_get_num_teams,  Up: Runtime Library Routines

2.14 `omp_get_num_threads' - Size of the active team
====================================================

_Description_:
     Returns the number of threads in the current team.  In a
     sequential section of the program `omp_get_num_threads' returns 1.

     The default team size may be initialized at startup by the
     `OMP_NUM_THREADS' environment variable.  At runtime, the size of
     the current team may be set either by the `NUM_THREADS' clause or
     by `omp_set_num_threads'.  If none of the above were used to
     define a specific value and `OMP_DYNAMIC' is disabled, one thread
     per CPU online is used.

_C/C++_:
     _Prototype_:  `int omp_get_num_threads(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_num_threads()'

_See also_:
     *note omp_get_max_threads::, *note omp_set_num_threads::, *note
     OMP_NUM_THREADS::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.2.


File: libgomp.info,  Node: omp_get_proc_bind,  Next: omp_get_schedule,  Prev: omp_get_num_threads,  Up: Runtime Library Routines

2.15 `omp_get_proc_bind' - Whether theads may be moved between CPUs
===================================================================

_Description_:
     This functions returns the currently active thread affinity
     policy, which is set via `OMP_PROC_BIND'.  Possible values are
     `omp_proc_bind_false', `omp_proc_bind_true',
     `omp_proc_bind_master', `omp_proc_bind_close' and
     `omp_proc_bind_spread'.

_C/C++_:
     _Prototype_:  `omp_proc_bind_t omp_get_proc_bind(void);'

_Fortran_:
     _Interface_:  `integer(kind=omp_proc_bind_kind) function
                   omp_get_proc_bind()'

_See also_:
     *note OMP_PROC_BIND::, *note OMP_PLACES::, *note
     GOMP_CPU_AFFINITY::,

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.22.


File: libgomp.info,  Node: omp_get_schedule,  Next: omp_get_team_num,  Prev: omp_get_proc_bind,  Up: Runtime Library Routines

2.16 `omp_get_schedule' - Obtain the runtime scheduling method
==============================================================

_Description_:
     Obtain the runtime scheduling method.  The KIND argument will be
     set to the value `omp_sched_static', `omp_sched_dynamic',
     `omp_sched_guided' or `omp_sched_auto'.  The second argument,
     CHUNK_SIZE, is set to the chunk size.

_C/C++_
     _Prototype_:  `void omp_get_schedule(omp_sched_t *kind, int
                   *chunk_size);'

_Fortran_:
     _Interface_:  `subroutine omp_get_schedule(kind, chunk_size)'
                   `integer(kind=omp_sched_kind) kind'
                   `integer chunk_size'

_See also_:
     *note omp_set_schedule::, *note OMP_SCHEDULE::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.13.


File: libgomp.info,  Node: omp_get_team_num,  Next: omp_get_team_size,  Prev: omp_get_schedule,  Up: Runtime Library Routines

2.17 `omp_get_team_num' - Get team number
=========================================

_Description_:
     Returns the team number of the calling thread.

_C/C++_:
     _Prototype_:  `int omp_get_team_num(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_team_num()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.33.


File: libgomp.info,  Node: omp_get_team_size,  Next: omp_get_thread_limit,  Prev: omp_get_team_num,  Up: Runtime Library Routines

2.18 `omp_get_team_size' - Number of threads in a team
======================================================

_Description_:
     This function returns the number of threads in a thread team to
     which either the current thread or its ancestor belongs.  For
     values of LEVEL outside zero to `omp_get_level', -1 is returned;
     if LEVEL is zero, 1 is returned, and for `omp_get_level', the
     result is identical to `omp_get_num_threads'.

_C/C++_:
     _Prototype_:  `int omp_get_team_size(int level);'

_Fortran_:
     _Interface_:  `integer function omp_get_team_size(level)'
                   `integer level'

_See also_:
     *note omp_get_num_threads::, *note omp_get_level::, *note
     omp_get_ancestor_thread_num::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.19.


File: libgomp.info,  Node: omp_get_thread_limit,  Next: omp_get_thread_num,  Prev: omp_get_team_size,  Up: Runtime Library Routines

2.19 `omp_get_thread_limit' - Maximum number of threads
=======================================================

_Description_:
     Return the maximum number of threads of the program.

_C/C++_:
     _Prototype_:  `int omp_get_thread_limit(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_thread_limit()'

_See also_:
     *note omp_get_max_threads::, *note OMP_THREAD_LIMIT::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.14.


File: libgomp.info,  Node: omp_get_thread_num,  Next: omp_in_parallel,  Prev: omp_get_thread_limit,  Up: Runtime Library Routines

2.20 `omp_get_thread_num' - Current thread ID
=============================================

_Description_:
     Returns a unique thread identification number within the current
     team.  In a sequential parts of the program, `omp_get_thread_num'
     always returns 0.  In parallel regions the return value varies
     from 0 to `omp_get_num_threads'-1 inclusive.  The return value of
     the master thread of a team is always 0.

_C/C++_:
     _Prototype_:  `int omp_get_thread_num(void);'

_Fortran_:
     _Interface_:  `integer function omp_get_thread_num()'

_See also_:
     *note omp_get_num_threads::, *note omp_get_ancestor_thread_num::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.4.


File: libgomp.info,  Node: omp_in_parallel,  Next: omp_in_final,  Prev: omp_get_thread_num,  Up: Runtime Library Routines

2.21 `omp_in_parallel' - Whether a parallel region is active
============================================================

_Description_:
     This function returns `true' if currently running in parallel,
     `false' otherwise.  Here, `true' and `false' represent their
     language-specific counterparts.

_C/C++_:
     _Prototype_:  `int omp_in_parallel(void);'

_Fortran_:
     _Interface_:  `logical function omp_in_parallel()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.6.


File: libgomp.info,  Node: omp_in_final,  Next: omp_is_initial_device,  Prev: omp_in_parallel,  Up: Runtime Library Routines

2.22 `omp_in_final' - Whether in final or included task region
==============================================================

_Description_:
     This function returns `true' if currently running in a final or
     included task region, `false' otherwise.  Here, `true' and `false'
     represent their language-specific counterparts.

_C/C++_:
     _Prototype_:  `int omp_in_final(void);'

_Fortran_:
     _Interface_:  `logical function omp_in_final()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.21.


File: libgomp.info,  Node: omp_is_initial_device,  Next: omp_set_default_device,  Prev: omp_in_final,  Up: Runtime Library Routines

2.23 `omp_is_initial_device' - Whether executing on the host device
===================================================================

_Description_:
     This function returns `true' if currently running on the host
     device, `false' otherwise.  Here, `true' and `false' represent
     their language-specific counterparts.

_C/C++_:
     _Prototype_:  `int omp_is_initial_device(void);'

_Fortran_:
     _Interface_:  `logical function omp_is_initial_device()'

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.34.


File: libgomp.info,  Node: omp_set_default_device,  Next: omp_set_dynamic,  Prev: omp_is_initial_device,  Up: Runtime Library Routines

2.24 `omp_set_default_device' - Set the default device for target regions
=========================================================================

_Description_:
     Set the default device for target regions without device clause.
     The argument shall be a nonnegative device number.

_C/C++_:
     _Prototype_:  `void omp_set_default_device(int device_num);'

_Fortran_:
     _Interface_:  `subroutine omp_set_default_device(device_num)'
                   `integer device_num'

_See also_:
     *note OMP_DEFAULT_DEVICE::, *note omp_get_default_device::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.29.


File: libgomp.info,  Node: omp_set_dynamic,  Next: omp_set_max_active_levels,  Prev: omp_set_default_device,  Up: Runtime Library Routines

2.25 `omp_set_dynamic' - Enable/disable dynamic teams
=====================================================

_Description_:
     Enable or disable the dynamic adjustment of the number of threads
     within a team.  The function takes the language-specific equivalent
     of `true' and `false', where `true' enables dynamic adjustment of
     team sizes and `false' disables it.

_C/C++_:
     _Prototype_:  `void omp_set_dynamic(int dynamic_threads);'

_Fortran_:
     _Interface_:  `subroutine omp_set_dynamic(dynamic_threads)'
                   `logical, intent(in) :: dynamic_threads'

_See also_:
     *note OMP_DYNAMIC::, *note omp_get_dynamic::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.7.


File: libgomp.info,  Node: omp_set_max_active_levels,  Next: omp_set_nested,  Prev: omp_set_dynamic,  Up: Runtime Library Routines

2.26 `omp_set_max_active_levels' - Limits the number of active parallel regions
===============================================================================

_Description_:
     This function limits the maximum allowed number of nested, active
     parallel regions.

_C/C++_
     _Prototype_:  `void omp_set_max_active_levels(int max_levels);'

_Fortran_:
     _Interface_:  `subroutine omp_set_max_active_levels(max_levels)'
                   `integer max_levels'

_See also_:
     *note omp_get_max_active_levels::, *note omp_get_active_level::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.15.


File: libgomp.info,  Node: omp_set_nested,  Next: omp_set_num_threads,  Prev: omp_set_max_active_levels,  Up: Runtime Library Routines

2.27 `omp_set_nested' - Enable/disable nested parallel regions
==============================================================

_Description_:
     Enable or disable nested parallel regions, i.e., whether team
     members are allowed to create new teams.  The function takes the
     language-specific equivalent of `true' and `false', where `true'
     enables dynamic adjustment of team sizes and `false' disables it.

_C/C++_:
     _Prototype_:  `void omp_set_nested(int nested);'

_Fortran_:
     _Interface_:  `subroutine omp_set_nested(nested)'
                   `logical, intent(in) :: nested'

_See also_:
     *note OMP_NESTED::, *note omp_get_nested::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.10.


File: libgomp.info,  Node: omp_set_num_threads,  Next: omp_set_schedule,  Prev: omp_set_nested,  Up: Runtime Library Routines

2.28 `omp_set_num_threads' - Set upper team size limit
======================================================

_Description_:
     Specifies the number of threads used by default in subsequent
     parallel sections, if those do not specify a `num_threads' clause.
     The argument of `omp_set_num_threads' shall be a positive integer.

_C/C++_:
     _Prototype_:  `void omp_set_num_threads(int num_threads);'

_Fortran_:
     _Interface_:  `subroutine omp_set_num_threads(num_threads)'
                   `integer, intent(in) :: num_threads'

_See also_:
     *note OMP_NUM_THREADS::, *note omp_get_num_threads::, *note
     omp_get_max_threads::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.1.


File: libgomp.info,  Node: omp_set_schedule,  Next: omp_init_lock,  Prev: omp_set_num_threads,  Up: Runtime Library Routines

2.29 `omp_set_schedule' - Set the runtime scheduling method
===========================================================

_Description_:
     Sets the runtime scheduling method.  The KIND argument can have the
     value `omp_sched_static', `omp_sched_dynamic', `omp_sched_guided'
     or `omp_sched_auto'.  Except for `omp_sched_auto', the chunk size
     is set to the value of CHUNK_SIZE if positive, or to the default
     value if zero or negative.  For `omp_sched_auto' the CHUNK_SIZE
     argument is ignored.

_C/C++_
     _Prototype_:  `void omp_set_schedule(omp_sched_t kind, int
                   chunk_size);'

_Fortran_:
     _Interface_:  `subroutine omp_set_schedule(kind, chunk_size)'
                   `integer(kind=omp_sched_kind) kind'
                   `integer chunk_size'

_See also_:
     *note omp_get_schedule:: *note OMP_SCHEDULE::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.2.12.


File: libgomp.info,  Node: omp_init_lock,  Next: omp_set_lock,  Prev: omp_set_schedule,  Up: Runtime Library Routines

2.30 `omp_init_lock' - Initialize simple lock
=============================================

_Description_:
     Initialize a simple lock.  After initialization, the lock is in an
     unlocked state.

_C/C++_:
     _Prototype_:  `void omp_init_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_init_lock(svar)'
                   `integer(omp_lock_kind), intent(out) :: svar'

_See also_:
     *note omp_destroy_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.1.


File: libgomp.info,  Node: omp_set_lock,  Next: omp_test_lock,  Prev: omp_init_lock,  Up: Runtime Library Routines

2.31 `omp_set_lock' - Wait for and set simple lock
==================================================

_Description_:
     Before setting a simple lock, the lock variable must be
     initialized by `omp_init_lock'.  The calling thread is blocked
     until the lock is available.  If the lock is already held by the
     current thread, a deadlock occurs.

_C/C++_:
     _Prototype_:  `void omp_set_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_set_lock(svar)'
                   `integer(omp_lock_kind), intent(inout) :: svar'

_See also_:
     *note omp_init_lock::, *note omp_test_lock::, *note
     omp_unset_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.4.


File: libgomp.info,  Node: omp_test_lock,  Next: omp_unset_lock,  Prev: omp_set_lock,  Up: Runtime Library Routines

2.32 `omp_test_lock' - Test and set simple lock if available
============================================================

_Description_:
     Before setting a simple lock, the lock variable must be
     initialized by `omp_init_lock'.  Contrary to `omp_set_lock',
     `omp_test_lock' does not block if the lock is not available.  This
     function returns `true' upon success, `false' otherwise.  Here,
     `true' and `false' represent their language-specific counterparts.

_C/C++_:
     _Prototype_:  `int omp_test_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `logical function omp_test_lock(svar)'
                   `integer(omp_lock_kind), intent(inout) :: svar'

_See also_:
     *note omp_init_lock::, *note omp_set_lock::, *note omp_set_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.6.


File: libgomp.info,  Node: omp_unset_lock,  Next: omp_destroy_lock,  Prev: omp_test_lock,  Up: Runtime Library Routines

2.33 `omp_unset_lock' - Unset simple lock
=========================================

_Description_:
     A simple lock about to be unset must have been locked by
     `omp_set_lock' or `omp_test_lock' before.  In addition, the lock
     must be held by the thread calling `omp_unset_lock'.  Then, the
     lock becomes unlocked.  If one or more threads attempted to set
     the lock before, one of them is chosen to, again, set the lock to
     itself.

_C/C++_:
     _Prototype_:  `void omp_unset_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_unset_lock(svar)'
                   `integer(omp_lock_kind), intent(inout) :: svar'

_See also_:
     *note omp_set_lock::, *note omp_test_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.5.


File: libgomp.info,  Node: omp_destroy_lock,  Next: omp_init_nest_lock,  Prev: omp_unset_lock,  Up: Runtime Library Routines

2.34 `omp_destroy_lock' - Destroy simple lock
=============================================

_Description_:
     Destroy a simple lock.  In order to be destroyed, a simple lock
     must be in the unlocked state.

_C/C++_:
     _Prototype_:  `void omp_destroy_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_destroy_lock(svar)'
                   `integer(omp_lock_kind), intent(inout) :: svar'

_See also_:
     *note omp_init_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.3.


File: libgomp.info,  Node: omp_init_nest_lock,  Next: omp_set_nest_lock,  Prev: omp_destroy_lock,  Up: Runtime Library Routines

2.35 `omp_init_nest_lock' - Initialize nested lock
==================================================

_Description_:
     Initialize a nested lock.  After initialization, the lock is in an
     unlocked state and the nesting count is set to zero.

_C/C++_:
     _Prototype_:  `void omp_init_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_init_nest_lock(nvar)'
                   `integer(omp_nest_lock_kind), intent(out) :: nvar'

_See also_:
     *note omp_destroy_nest_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.1.


File: libgomp.info,  Node: omp_set_nest_lock,  Next: omp_test_nest_lock,  Prev: omp_init_nest_lock,  Up: Runtime Library Routines

2.36 `omp_set_nest_lock' - Wait for and set nested lock
=======================================================

_Description_:
     Before setting a nested lock, the lock variable must be
     initialized by `omp_init_nest_lock'.  The calling thread is
     blocked until the lock is available.  If the lock is already held
     by the current thread, the nesting count for the lock is
     incremented.

_C/C++_:
     _Prototype_:  `void omp_set_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_set_nest_lock(nvar)'
                   `integer(omp_nest_lock_kind), intent(inout) :: nvar'

_See also_:
     *note omp_init_nest_lock::, *note omp_unset_nest_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.4.


File: libgomp.info,  Node: omp_test_nest_lock,  Next: omp_unset_nest_lock,  Prev: omp_set_nest_lock,  Up: Runtime Library Routines

2.37 `omp_test_nest_lock' - Test and set nested lock if available
=================================================================

_Description_:
     Before setting a nested lock, the lock variable must be
     initialized by `omp_init_nest_lock'.  Contrary to
     `omp_set_nest_lock', `omp_test_nest_lock' does not block if the
     lock is not available.  If the lock is already held by the current
     thread, the new nesting count is returned.  Otherwise, the return
     value equals zero.

_C/C++_:
     _Prototype_:  `int omp_test_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `logical function omp_test_nest_lock(nvar)'
                   `integer(omp_nest_lock_kind), intent(inout) :: nvar'

_See also_:
     *note omp_init_lock::, *note omp_set_lock::, *note omp_set_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.6.


File: libgomp.info,  Node: omp_unset_nest_lock,  Next: omp_destroy_nest_lock,  Prev: omp_test_nest_lock,  Up: Runtime Library Routines

2.38 `omp_unset_nest_lock' - Unset nested lock
==============================================

_Description_:
     A nested lock about to be unset must have been locked by
     `omp_set_nested_lock' or `omp_test_nested_lock' before.  In
     addition, the lock must be held by the thread calling
     `omp_unset_nested_lock'.  If the nesting count drops to zero, the
     lock becomes unlocked.  If one ore more threads attempted to set
     the lock before, one of them is chosen to, again, set the lock to
     itself.

_C/C++_:
     _Prototype_:  `void omp_unset_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_unset_nest_lock(nvar)'
                   `integer(omp_nest_lock_kind), intent(inout) :: nvar'

_See also_:
     *note omp_set_nest_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.5.


File: libgomp.info,  Node: omp_destroy_nest_lock,  Next: omp_get_wtick,  Prev: omp_unset_nest_lock,  Up: Runtime Library Routines

2.39 `omp_destroy_nest_lock' - Destroy nested lock
==================================================

_Description_:
     Destroy a nested lock.  In order to be destroyed, a nested lock
     must be in the unlocked state and its nesting count must equal
     zero.

_C/C++_:
     _Prototype_:  `void omp_destroy_nest_lock(omp_nest_lock_t *);'

_Fortran_:
     _Interface_:  `subroutine omp_destroy_nest_lock(nvar)'
                   `integer(omp_nest_lock_kind), intent(inout) :: nvar'

_See also_:
     *note omp_init_lock::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.3.3.


File: libgomp.info,  Node: omp_get_wtick,  Next: omp_get_wtime,  Prev: omp_destroy_nest_lock,  Up: Runtime Library Routines

2.40 `omp_get_wtick' - Get timer precision
==========================================

_Description_:
     Gets the timer precision, i.e., the number of seconds between two
     successive clock ticks.

_C/C++_:
     _Prototype_:  `double omp_get_wtick(void);'

_Fortran_:
     _Interface_:  `double precision function omp_get_wtick()'

_See also_:
     *note omp_get_wtime::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.4.2.


File: libgomp.info,  Node: omp_get_wtime,  Prev: omp_get_wtick,  Up: Runtime Library Routines

2.41 `omp_get_wtime' - Elapsed wall clock time
==============================================

_Description_:
     Elapsed wall clock time in seconds.  The time is measured per
     thread, no guarantee can be made that two distinct threads measure
     the same time.  Time is measured from some "time in the past",
     which is an arbitrary time guaranteed not to change during the
     execution of the program.

_C/C++_:
     _Prototype_:  `double omp_get_wtime(void);'

_Fortran_:
     _Interface_:  `double precision function omp_get_wtime()'

_See also_:
     *note omp_get_wtick::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 3.4.1.


File: libgomp.info,  Node: Environment Variables,  Next: Enabling OpenACC,  Prev: Runtime Library Routines,  Up: Top

3 OpenMP Environment Variables
******************************

The environment variables which beginning with `OMP_' are defined by
section 4 of the OpenMP specification in version 4.5, while those
beginning with `GOMP_' are GNU extensions.

* Menu:

* OMP_CANCELLATION::        Set whether cancellation is activated
* OMP_DISPLAY_ENV::         Show OpenMP version and environment variables
* OMP_DEFAULT_DEVICE::      Set the device used in target regions
* OMP_DYNAMIC::             Dynamic adjustment of threads
* OMP_MAX_ACTIVE_LEVELS::   Set the maximum number of nested parallel regions
* OMP_MAX_TASK_PRIORITY::   Set the maximum task priority value
* OMP_NESTED::              Nested parallel regions
* OMP_NUM_THREADS::         Specifies the number of threads to use
* OMP_PROC_BIND::           Whether theads may be moved between CPUs
* OMP_PLACES::              Specifies on which CPUs the theads should be placed
* OMP_STACKSIZE::           Set default thread stack size
* OMP_SCHEDULE::            How threads are scheduled
* OMP_THREAD_LIMIT::        Set the maximum number of threads
* OMP_WAIT_POLICY::         How waiting threads are handled
* GOMP_CPU_AFFINITY::       Bind threads to specific CPUs
* GOMP_DEBUG::              Enable debugging output
* GOMP_STACKSIZE::          Set default thread stack size
* GOMP_SPINCOUNT::          Set the busy-wait spin count
* GOMP_RTEMS_THREAD_POOLS:: Set the RTEMS specific thread pools


File: libgomp.info,  Node: OMP_CANCELLATION,  Next: OMP_DISPLAY_ENV,  Up: Environment Variables

3.1 `OMP_CANCELLATION' - Set whether cancellation is activated
==============================================================

_Description_:
     If set to `TRUE', the cancellation is activated.  If set to
     `FALSE' or if unset, cancellation is disabled and the `cancel'
     construct is ignored.

_See also_:
     *note omp_get_cancellation::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.11


File: libgomp.info,  Node: OMP_DISPLAY_ENV,  Next: OMP_DEFAULT_DEVICE,  Prev: OMP_CANCELLATION,  Up: Environment Variables

3.2 `OMP_DISPLAY_ENV' - Show OpenMP version and environment variables
=====================================================================

_Description_:
     If set to `TRUE', the OpenMP version number and the values
     associated with the OpenMP environment variables are printed to
     `stderr'.  If set to `VERBOSE', it additionally shows the value of
     the environment variables which are GNU extensions.  If undefined
     or set to `FALSE', this information will not be shown.

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.12


File: libgomp.info,  Node: OMP_DEFAULT_DEVICE,  Next: OMP_DYNAMIC,  Prev: OMP_DISPLAY_ENV,  Up: Environment Variables

3.3 `OMP_DEFAULT_DEVICE' - Set the device used in target regions
================================================================

_Description_:
     Set to choose the device which is used in a `target' region,
     unless the value is overridden by `omp_set_default_device' or by a
     `device' clause.  The value shall be the nonnegative device
     number. If no device with the given device number exists, the code
     is executed on the host.  If unset, device number 0 will be used.

_See also_:
     *note omp_get_default_device::, *note omp_set_default_device::,

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.13


File: libgomp.info,  Node: OMP_DYNAMIC,  Next: OMP_MAX_ACTIVE_LEVELS,  Prev: OMP_DEFAULT_DEVICE,  Up: Environment Variables

3.4 `OMP_DYNAMIC' - Dynamic adjustment of threads
=================================================

_Description_:
     Enable or disable the dynamic adjustment of the number of threads
     within a team.  The value of this environment variable shall be
     `TRUE' or `FALSE'.  If undefined, dynamic adjustment is disabled
     by default.

_See also_:
     *note omp_set_dynamic::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.3


File: libgomp.info,  Node: OMP_MAX_ACTIVE_LEVELS,  Next: OMP_MAX_TASK_PRIORITY,  Prev: OMP_DYNAMIC,  Up: Environment Variables

3.5 `OMP_MAX_ACTIVE_LEVELS' - Set the maximum number of nested parallel regions
===============================================================================

_Description_:
     Specifies the initial value for the maximum number of nested
     parallel regions.  The value of this variable shall be a positive
     integer.  If undefined, the number of active levels is unlimited.

_See also_:
     *note omp_set_max_active_levels::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.9


File: libgomp.info,  Node: OMP_MAX_TASK_PRIORITY,  Next: OMP_NESTED,  Prev: OMP_MAX_ACTIVE_LEVELS,  Up: Environment Variables

3.6 `OMP_MAX_TASK_PRIORITY' - Set the maximum priority
======================================================

number that can be set for a task.  
_Description_:
     Specifies the initial value for the maximum priority value that
     can be set for a task.  The value of this variable shall be a
     non-negative integer, and zero is allowed.  If undefined, the
     default priority is 0.

_See also_:
     *note omp_get_max_task_priority::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.14


File: libgomp.info,  Node: OMP_NESTED,  Next: OMP_NUM_THREADS,  Prev: OMP_MAX_TASK_PRIORITY,  Up: Environment Variables

3.7 `OMP_NESTED' - Nested parallel regions
==========================================

_Description_:
     Enable or disable nested parallel regions, i.e., whether team
     members are allowed to create new teams.  The value of this
     environment variable shall be `TRUE' or `FALSE'.  If undefined,
     nested parallel regions are disabled by default.

_See also_:
     *note omp_set_nested::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.6


File: libgomp.info,  Node: OMP_NUM_THREADS,  Next: OMP_PROC_BIND,  Prev: OMP_NESTED,  Up: Environment Variables

3.8 `OMP_NUM_THREADS' - Specifies the number of threads to use
==============================================================

_Description_:
     Specifies the default number of threads to use in parallel
     regions.  The value of this variable shall be a comma-separated
     list of positive integers; the value specified the number of
     threads to use for the corresponding nested level.  If undefined
     one thread per CPU is used.

_See also_:
     *note omp_set_num_threads::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.2


File: libgomp.info,  Node: OMP_PROC_BIND,  Next: OMP_PLACES,  Prev: OMP_NUM_THREADS,  Up: Environment Variables

3.9 `OMP_PROC_BIND' - Whether theads may be moved between CPUs
==============================================================

_Description_:
     Specifies whether threads may be moved between processors.  If set
     to `TRUE', OpenMP theads should not be moved; if set to `FALSE'
     they may be moved.  Alternatively, a comma separated list with the
     values `MASTER', `CLOSE' and `SPREAD' can be used to specify the
     thread affinity policy for the corresponding nesting level.  With
     `MASTER' the worker threads are in the same place partition as the
     master thread.  With `CLOSE' those are kept close to the master
     thread in contiguous place partitions.  And with `SPREAD' a sparse
     distribution across the place partitions is used.

     When undefined, `OMP_PROC_BIND' defaults to `TRUE' when
     `OMP_PLACES' or `GOMP_CPU_AFFINITY' is set and `FALSE' otherwise.

_See also_:
     *note OMP_PLACES::, *note GOMP_CPU_AFFINITY::, *note
     omp_get_proc_bind::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.4


File: libgomp.info,  Node: OMP_PLACES,  Next: OMP_STACKSIZE,  Prev: OMP_PROC_BIND,  Up: Environment Variables

3.10 `OMP_PLACES' - Specifies on which CPUs the theads should be placed
=======================================================================

_Description_:
     The thread placement can be either specified using an abstract
     name or by an explicit list of the places.  The abstract names
     `threads', `cores' and `sockets' can be optionally followed by a
     positive number in parentheses, which denotes the how many places
     shall be created.  With `threads' each place corresponds to a
     single hardware thread; `cores' to a single core with the
     corresponding number of hardware threads; and with `sockets' the
     place corresponds to a single socket.  The resulting placement can
     be shown by setting the `OMP_DISPLAY_ENV' environment variable.

     Alternatively, the placement can be specified explicitly as
     comma-separated list of places.  A place is specified by set of
     nonnegative numbers in curly braces, denoting the denoting the
     hardware threads.  The hardware threads belonging to a place can
     either be specified as comma-separated list of nonnegative thread
     numbers or using an interval.  Multiple places can also be either
     specified by a comma-separated list of places or by an interval.
     To specify an interval, a colon followed by the count is placed
     after after the hardware thread number or the place.  Optionally,
     the length can be followed by a colon and the stride number -
     otherwise a unit stride is assumed.  For instance, the following
     specifies the same places list: `"{0,1,2}, {3,4,6}, {7,8,9},
     {10,11,12}"'; `"{0:3}, {3:3}, {7:3}, {10:3}"'; and `"{0:2}:4:3"'.

     If `OMP_PLACES' and `GOMP_CPU_AFFINITY' are unset and
     `OMP_PROC_BIND' is either unset or `false', threads may be moved
     between CPUs following no placement policy.

_See also_:
     *note OMP_PROC_BIND::, *note GOMP_CPU_AFFINITY::, *note
     omp_get_proc_bind::, *note OMP_DISPLAY_ENV::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.5


File: libgomp.info,  Node: OMP_STACKSIZE,  Next: OMP_SCHEDULE,  Prev: OMP_PLACES,  Up: Environment Variables

3.11 `OMP_STACKSIZE' - Set default thread stack size
====================================================

_Description_:
     Set the default thread stack size in kilobytes, unless the number
     is suffixed by `B', `K', `M' or `G', in which case the size is,
     respectively, in bytes, kilobytes, megabytes or gigabytes.  This
     is different from `pthread_attr_setstacksize' which gets the
     number of bytes as an argument.  If the stack size cannot be set
     due to system constraints, an error is reported and the initial
     stack size is left unchanged.  If undefined, the stack size is
     system dependent.

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.7


File: libgomp.info,  Node: OMP_SCHEDULE,  Next: OMP_THREAD_LIMIT,  Prev: OMP_STACKSIZE,  Up: Environment Variables

3.12 `OMP_SCHEDULE' - How threads are scheduled
===============================================

_Description_:
     Allows to specify `schedule type' and `chunk size'.  The value of
     the variable shall have the form: `type[,chunk]' where `type' is
     one of `static', `dynamic', `guided' or `auto' The optional
     `chunk' size shall be a positive integer.  If undefined, dynamic
     scheduling and a chunk size of 1 is used.

_See also_:
     *note omp_set_schedule::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Sections
     2.7.1.1 and 4.1


File: libgomp.info,  Node: OMP_THREAD_LIMIT,  Next: OMP_WAIT_POLICY,  Prev: OMP_SCHEDULE,  Up: Environment Variables

3.13 `OMP_THREAD_LIMIT' - Set the maximum number of threads
===========================================================

_Description_:
     Specifies the number of threads to use for the whole program.  The
     value of this variable shall be a positive integer.  If undefined,
     the number of threads is not limited.

_See also_:
     *note OMP_NUM_THREADS::, *note omp_get_thread_limit::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.10


File: libgomp.info,  Node: OMP_WAIT_POLICY,  Next: GOMP_CPU_AFFINITY,  Prev: OMP_THREAD_LIMIT,  Up: Environment Variables

3.14 `OMP_WAIT_POLICY' - How waiting threads are handled
========================================================

_Description_:
     Specifies whether waiting threads should be active or passive.  If
     the value is `PASSIVE', waiting threads should not consume CPU
     power while waiting; while the value is `ACTIVE' specifies that
     they should.  If undefined, threads wait actively for a short time
     before waiting passively.

_See also_:
     *note GOMP_SPINCOUNT::

_Reference_:
     OpenMP specification v4.5 (https://www.openmp.org), Section 4.8


File: libgomp.info,  Node: GOMP_CPU_AFFINITY,  Next: GOMP_DEBUG,  Prev: OMP_WAIT_POLICY,  Up: Environment Variables

3.15 `GOMP_CPU_AFFINITY' - Bind threads to specific CPUs
========================================================

_Description_:
     Binds threads to specific CPUs.  The variable should contain a
     space-separated or comma-separated list of CPUs.  This list may
     contain different kinds of entries: either single CPU numbers in
     any order, a range of CPUs (M-N) or a range with some stride
     (M-N:S).  CPU numbers are zero based.  For example,
     `GOMP_CPU_AFFINITY="0 3 1-2 4-15:2"' will bind the initial thread
     to CPU 0, the second to CPU 3, the third to CPU 1, the fourth to
     CPU 2, the fifth to CPU 4, the sixth through tenth to CPUs 6, 8,
     10, 12, and 14 respectively and then start assigning back from the
     beginning of the list.  `GOMP_CPU_AFFINITY=0' binds all threads to
     CPU 0.

     There is no libgomp library routine to determine whether a CPU
     affinity specification is in effect.  As a workaround,
     language-specific library functions, e.g., `getenv' in C or
     `GET_ENVIRONMENT_VARIABLE' in Fortran, may be used to query the
     setting of the `GOMP_CPU_AFFINITY' environment variable.  A
     defined CPU affinity on startup cannot be changed or disabled
     during the runtime of the application.

     If both `GOMP_CPU_AFFINITY' and `OMP_PROC_BIND' are set,
     `OMP_PROC_BIND' has a higher precedence.  If neither has been set
     and `OMP_PROC_BIND' is unset, or when `OMP_PROC_BIND' is set to
     `FALSE', the host system will handle the assignment of threads to
     CPUs.

_See also_:
     *note OMP_PLACES::, *note OMP_PROC_BIND::


File: libgomp.info,  Node: GOMP_DEBUG,  Next: GOMP_STACKSIZE,  Prev: GOMP_CPU_AFFINITY,  Up: Environment Variables

3.16 `GOMP_DEBUG' - Enable debugging output
===========================================

_Description_:
     Enable debugging output.  The variable should be set to `0'
     (disabled, also the default if not set), or `1' (enabled).

     If enabled, some debugging output will be printed during execution.
     This is currently not specified in more detail, and subject to
     change.


File: libgomp.info,  Node: GOMP_STACKSIZE,  Next: GOMP_SPINCOUNT,  Prev: GOMP_DEBUG,  Up: Environment Variables

3.17 `GOMP_STACKSIZE' - Set default thread stack size
=====================================================

_Description_:
     Set the default thread stack size in kilobytes.  This is different
     from `pthread_attr_setstacksize' which gets the number of bytes as
     an argument.  If the stack size cannot be set due to system
     constraints, an error is reported and the initial stack size is
     left unchanged.  If undefined, the stack size is system dependent.

_See also_:
     *note OMP_STACKSIZE::

_Reference_:
     GCC Patches Mailinglist
     (http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00493.html), GCC
     Patches Mailinglist
     (http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00496.html)


File: libgomp.info,  Node: GOMP_SPINCOUNT,  Next: GOMP_RTEMS_THREAD_POOLS,  Prev: GOMP_STACKSIZE,  Up: Environment Variables

3.18 `GOMP_SPINCOUNT' - Set the busy-wait spin count
====================================================

_Description_:
     Determines how long a threads waits actively with consuming CPU
     power before waiting passively without consuming CPU power.  The
     value may be either `INFINITE', `INFINITY' to always wait actively
     or an integer which gives the number of spins of the busy-wait
     loop.  The integer may optionally be followed by the following
     suffixes acting as multiplication factors: `k' (kilo, thousand),
     `M' (mega, million), `G' (giga, billion), or `T' (tera, trillion).
     If undefined, 0 is used when `OMP_WAIT_POLICY' is `PASSIVE',
     300,000 is used when `OMP_WAIT_POLICY' is undefined and 30 billion
     is used when `OMP_WAIT_POLICY' is `ACTIVE'.  If there are more
     OpenMP threads than available CPUs, 1000 and 100 spins are used
     for `OMP_WAIT_POLICY' being `ACTIVE' or undefined, respectively;
     unless the `GOMP_SPINCOUNT' is lower or `OMP_WAIT_POLICY' is
     `PASSIVE'.

_See also_:
     *note OMP_WAIT_POLICY::


File: libgomp.info,  Node: GOMP_RTEMS_THREAD_POOLS,  Prev: GOMP_SPINCOUNT,  Up: Environment Variables

3.19 `GOMP_RTEMS_THREAD_POOLS' - Set the RTEMS specific thread pools
====================================================================

_Description_:
     This environment variable is only used on the RTEMS real-time
     operating system.  It determines the scheduler instance specific
     thread pools.  The format for `GOMP_RTEMS_THREAD_POOLS' is a list
     of optional `<thread-pool-count>[$<priority>]@<scheduler-name>'
     configurations separated by `:' where:
        * `<thread-pool-count>' is the thread pool count for this
          scheduler instance.

        * `$<priority>' is an optional priority for the worker threads
          of a thread pool according to `pthread_setschedparam'.  In
          case a priority value is omitted, then a worker thread will
          inherit the priority of the OpenMP master thread that created
          it.  The priority of the worker thread is not changed after
          creation, even if a new OpenMP master thread using the worker
          has a different priority.

        * `@<scheduler-name>' is the scheduler instance name according
          to the RTEMS application configuration.
     In case no thread pool configuration is specified for a scheduler
     instance, then each OpenMP master thread of this scheduler
     instance will use its own dynamically allocated thread pool.  To
     limit the worker thread count of the thread pools, each OpenMP
     master thread must call `omp_set_num_threads'.

_Example_:
     Lets suppose we have three scheduler instances `IO', `WRK0', and
     `WRK1' with `GOMP_RTEMS_THREAD_POOLS' set to `"1@WRK0:3$4@WRK1"'.
     Then there are no thread pool restrictions for scheduler instance
     `IO'.  In the scheduler instance `WRK0' there is one thread pool
     available.  Since no priority is specified for this scheduler
     instance, the worker thread inherits the priority of the OpenMP
     master thread that created it.  In the scheduler instance `WRK1'
     there are three thread pools available and their worker threads
     run at priority four.


File: libgomp.info,  Node: Enabling OpenACC,  Next: OpenACC Runtime Library Routines,  Prev: Environment Variables,  Up: Top

4 Enabling OpenACC
******************

To activate the OpenACC extensions for C/C++ and Fortran, the
compile-time flag `-fopenacc' must be specified.  This enables the
OpenACC directive `#pragma acc' in C/C++ and `!$accp' directives in
free form, `c$acc', `*$acc' and `!$acc' directives in fixed form, `!$'
conditional compilation sentinels in free form and `c$', `*$' and `!$'
sentinels in fixed form, for Fortran.  The flag also arranges for
automatic linking of the OpenACC runtime library (*note OpenACC Runtime
Library Routines::).

   A complete description of all OpenACC directives accepted may be
found in the OpenACC (https://www.openacc.org) Application Programming
Interface manual, version 2.0.

   Note that this is an experimental feature and subject to change in
future versions of GCC.  See `https://gcc.gnu.org/wiki/OpenACC' for
more information.


File: libgomp.info,  Node: OpenACC Runtime Library Routines,  Next: OpenACC Environment Variables,  Prev: Enabling OpenACC,  Up: Top

5 OpenACC Runtime Library Routines
**********************************

The runtime routines described here are defined by section 3 of the
OpenACC specifications in version 2.0.  They have C linkage, and do not
throw exceptions.  Generally, they are available only for the host,
with the exception of `acc_on_device', which is available for both the
host and the acceleration device.

* Menu:

* acc_get_num_devices::         Get number of devices for the given device
                                type.
* acc_set_device_type::         Set type of device accelerator to use.
* acc_get_device_type::         Get type of device accelerator to be used.
* acc_set_device_num::          Set device number to use.
* acc_get_device_num::          Get device number to be used.
* acc_async_test::              Tests for completion of a specific asynchronous
                                operation.
* acc_async_test_all::          Tests for completion of all asychronous
                                operations.
* acc_wait::                    Wait for completion of a specific asynchronous
                                operation.
* acc_wait_all::                Waits for completion of all asyncrhonous
                                operations.
* acc_wait_all_async::          Wait for completion of all asynchronous
                                operations.
* acc_wait_async::              Wait for completion of asynchronous operations.
* acc_init::                    Initialize runtime for a specific device type.
* acc_shutdown::                Shuts down the runtime for a specific device
                                type.
* acc_on_device::               Whether executing on a particular device
* acc_malloc::                  Allocate device memory.
* acc_free::                    Free device memory.
* acc_copyin::                  Allocate device memory and copy host memory to
                                it.
* acc_present_or_copyin::       If the data is not present on the device,
                                allocate device memory and copy from host
                                memory.
* acc_create::                  Allocate device memory and map it to host
                                memory.
* acc_present_or_create::       If the data is not present on the device,
                                allocate device memory and map it to host
                                memory.
* acc_copyout::                 Copy device memory to host memory.
* acc_delete::                  Free device memory.
* acc_update_device::           Update device memory from mapped host memory.
* acc_update_self::             Update host memory from mapped device memory.
* acc_map_data::                Map previously allocated device memory to host
                                memory.
* acc_unmap_data::              Unmap device memory from host memory.
* acc_deviceptr::               Get device pointer associated with specific
                                host address.
* acc_hostptr::                 Get host pointer associated with specific
                                device address.
* acc_is_present::              Indiciate whether host variable / array is
                                present on device.
* acc_memcpy_to_device::        Copy host memory to device memory.
* acc_memcpy_from_device::      Copy device memory to host memory.

API routines for target platforms.

* acc_get_current_cuda_device:: Get CUDA device handle.
* acc_get_current_cuda_context::Get CUDA context handle.
* acc_get_cuda_stream::         Get CUDA stream handle.
* acc_set_cuda_stream::         Set CUDA stream handle.


File: libgomp.info,  Node: acc_get_num_devices,  Next: acc_set_device_type,  Up: OpenACC Runtime Library Routines

5.1 `acc_get_num_devices' - Get number of devices for given device type
=======================================================================

_Description_
     This function returns a value indicating the number of devices
     available for the device type specified in DEVICETYPE.

_C/C++_:
     _Prototype_:  `int acc_get_num_devices(acc_device_t devicetype);'

_Fortran_:
     _Interface_:  `integer function acc_get_num_devices(devicetype)'
                   `integer(kind=acc_device_kind) devicetype'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.1.


File: libgomp.info,  Node: acc_set_device_type,  Next: acc_get_device_type,  Prev: acc_get_num_devices,  Up: OpenACC Runtime Library Routines

5.2 `acc_set_device_type' - Set type of device accelerator to use.
==================================================================

_Description_
     This function indicates to the runtime library which device typr,
     specified in DEVICETYPE, to use when executing a parallel or
     kernels region.

_C/C++_:
     _Prototype_:  `acc_set_device_type(acc_device_t devicetype);'

_Fortran_:
     _Interface_:  `subroutine acc_set_device_type(devicetype)'
                   `integer(kind=acc_device_kind) devicetype'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.2.


File: libgomp.info,  Node: acc_get_device_type,  Next: acc_set_device_num,  Prev: acc_set_device_type,  Up: OpenACC Runtime Library Routines

5.3 `acc_get_device_type' - Get type of device accelerator to be used.
======================================================================

_Description_
     This function returns what device type will be used when executing
     a parallel or kernels region.

_C/C++_:
     _Prototype_:  `acc_device_t acc_get_device_type(void);'

_Fortran_:
     _Interface_:  `function acc_get_device_type(void)'
                   `integer(kind=acc_device_kind) acc_get_device_type'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.3.


File: libgomp.info,  Node: acc_set_device_num,  Next: acc_get_device_num,  Prev: acc_get_device_type,  Up: OpenACC Runtime Library Routines

5.4 `acc_set_device_num' - Set device number to use.
====================================================

_Description_
     This function will indicate to the runtime which device number,
     specified by NUM, associated with the specifed device type
     DEVICETYPE.

_C/C++_:
     _Prototype_:  `acc_set_device_num(int num, acc_device_t
                   devicetype);'

_Fortran_:
     _Interface_:  `subroutine acc_set_device_num(devicenum, devicetype)'
                   `integer devicenum'
                   `integer(kind=acc_device_kind) devicetype'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.4.


File: libgomp.info,  Node: acc_get_device_num,  Next: acc_async_test,  Prev: acc_set_device_num,  Up: OpenACC Runtime Library Routines

5.5 `acc_get_device_num' - Get device number to be used.
========================================================

_Description_
     This function returns which device number associated with the
     specified device type DEVICETYPE, will be used when executing a
     parallel or kernels region.

_C/C++_:
     _Prototype_:  `int acc_get_device_num(acc_device_t devicetype);'

_Fortran_:
     _Interface_:  `function acc_get_device_num(devicetype)'
                   `integer(kind=acc_device_kind) devicetype'
                   `integer acc_get_device_num'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.5.


File: libgomp.info,  Node: acc_async_test,  Next: acc_async_test_all,  Prev: acc_get_device_num,  Up: OpenACC Runtime Library Routines

5.6 `acc_async_test' - Test for completion of a specific asynchronous operation.
================================================================================

_Description_
     This function tests for completion of the asynchrounous operation
     specified in ARG. In C/C++, a non-zero value will be returned to
     indicate the specified asynchronous operation has completed. While
     Fortran will return a `true'. If the asynchrounous operation has
     not completed, C/C++ returns a zero and Fortran returns a `false'.

_C/C++_:
     _Prototype_:  `int acc_async_test(int arg);'

_Fortran_:
     _Interface_:  `function acc_async_test(arg)'
                   `integer(kind=acc_handle_kind) arg'
                   `logical acc_async_test'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.6.


File: libgomp.info,  Node: acc_async_test_all,  Next: acc_wait,  Prev: acc_async_test,  Up: OpenACC Runtime Library Routines

5.7 `acc_async_test_all' - Tests for completion of all asynchronous operations.
===============================================================================

_Description_
     This function tests for completion of all asynchrounous operations.
     In C/C++, a non-zero value will be returned to indicate all
     asynchronous operations have completed. While Fortran will return
     a `true'. If any asynchronous operation has not completed, C/C++
     returns a zero and Fortran returns a `false'.

_C/C++_:
     _Prototype_:  `int acc_async_test_all(void);'

_Fortran_:
     _Interface_:  `function acc_async_test()'
                   `logical acc_get_device_num'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.7.


File: libgomp.info,  Node: acc_wait,  Next: acc_wait_all,  Prev: acc_async_test_all,  Up: OpenACC Runtime Library Routines

5.8 `acc_wait' - Wait for completion of a specific asynchronous operation.
==========================================================================

_Description_
     This function waits for completion of the asynchronous operation
     specified in ARG.

_C/C++_:
     _Prototype_:  `acc_wait(arg);'
     _Prototype    `acc_async_wait(arg);'
     (OpenACC 1.0  
     compatibility)_:

_Fortran_:
     _Interface_:  `subroutine acc_wait(arg)'
                   `integer(acc_handle_kind) arg'
     _Interface    `subroutine acc_async_wait(arg)'
     (OpenACC 1.0  
     compatibility)_:
                   `integer(acc_handle_kind) arg'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.8.


File: libgomp.info,  Node: acc_wait_all,  Next: acc_wait_all_async,  Prev: acc_wait,  Up: OpenACC Runtime Library Routines

5.9 `acc_wait_all' - Waits for completion of all asynchronous operations.
=========================================================================

_Description_
     This function waits for the completion of all asynchronous
     operations.

_C/C++_:
     _Prototype_:  `acc_wait_all(void);'
     _Prototype    `acc_async_wait_all(void);'
     (OpenACC 1.0  
     compatibility)_:

_Fortran_:
     _Interface_:  `subroutine acc_wait_all()'
     _Interface    `subroutine acc_async_wait_all()'
     (OpenACC 1.0  
     compatibility)_:

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.10.


File: libgomp.info,  Node: acc_wait_all_async,  Next: acc_wait_async,  Prev: acc_wait_all,  Up: OpenACC Runtime Library Routines

5.10 `acc_wait_all_async' - Wait for completion of all asynchronous operations.
===============================================================================

_Description_
     This function enqueues a wait operation on the queue ASYNC for any
     and all asynchronous operations that have been previously enqueued
     on any queue.

_C/C++_:
     _Prototype_:  `acc_wait_all_async(int async);'

_Fortran_:
     _Interface_:  `subroutine acc_wait_all_async(async)'
                   `integer(acc_handle_kind) async'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.11.


File: libgomp.info,  Node: acc_wait_async,  Next: acc_init,  Prev: acc_wait_all_async,  Up: OpenACC Runtime Library Routines

5.11 `acc_wait_async' - Wait for completion of asynchronous operations.
=======================================================================

_Description_
     This function enqueues a wait operation on queue ASYNC for any and
     all asynchronous operations enqueued on queue ARG.

_C/C++_:
     _Prototype_:  `acc_wait_async(int arg, int async);'

_Fortran_:
     _Interface_:  `subroutine acc_wait_async(arg, async)'
                   `integer(acc_handle_kind) arg, async'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.9.


File: libgomp.info,  Node: acc_init,  Next: acc_shutdown,  Prev: acc_wait_async,  Up: OpenACC Runtime Library Routines

5.12 `acc_init' - Initialize runtime for a specific device type.
================================================================

_Description_
     This function initializes the runtime for the device type
     specified in DEVICETYPE.

_C/C++_:
     _Prototype_:  `acc_init(acc_device_t devicetype);'

_Fortran_:
     _Interface_:  `subroutine acc_init(devicetype)'
                   `integer(acc_device_kind) devicetype'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.12.


File: libgomp.info,  Node: acc_shutdown,  Next: acc_on_device,  Prev: acc_init,  Up: OpenACC Runtime Library Routines

5.13 `acc_shutdown' - Shuts down the runtime for a specific device type.
========================================================================

_Description_
     This function shuts down the runtime for the device type specified
     in DEVICETYPE.

_C/C++_:
     _Prototype_:  `acc_shutdown(acc_device_t devicetype);'

_Fortran_:
     _Interface_:  `subroutine acc_shutdown(devicetype)'
                   `integer(acc_device_kind) devicetype'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.13.


File: libgomp.info,  Node: acc_on_device,  Next: acc_malloc,  Prev: acc_shutdown,  Up: OpenACC Runtime Library Routines

5.14 `acc_on_device' - Whether executing on a particular device
===============================================================

_Description_:
     This function returns whether the program is executing on a
     particular device specified in DEVICETYPE. In C/C++ a non-zero
     value is returned to indicate the device is execiting on the
     specified device type.  In Fortran, `true' will be returned. If
     the program is not executing on the specified device type C/C++
     will return a zero, while Fortran will return `false'.

_C/C++_:
     _Prototype_:  `acc_on_device(acc_device_t devicetype);'

_Fortran_:
     _Interface_:  `function acc_on_device(devicetype)'
                   `integer(acc_device_kind) devicetype'
                   `logical acc_on_device'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.14.


File: libgomp.info,  Node: acc_malloc,  Next: acc_free,  Prev: acc_on_device,  Up: OpenACC Runtime Library Routines

5.15 `acc_malloc' - Allocate device memory.
===========================================

_Description_
     This function allocates LEN bytes of device memory. It returns the
     device address of the allocated memory.

_C/C++_:
     _Prototype_:  `d_void* acc_malloc(size_t len);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.15.


File: libgomp.info,  Node: acc_free,  Next: acc_copyin,  Prev: acc_malloc,  Up: OpenACC Runtime Library Routines

5.16 `acc_free' - Free device memory.
=====================================

_Description_
     Free previously allocated device memory at the device address `a'.

_C/C++_:
     _Prototype_:  `acc_free(d_void *a);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.16.


File: libgomp.info,  Node: acc_copyin,  Next: acc_present_or_copyin,  Prev: acc_free,  Up: OpenACC Runtime Library Routines

5.17 `acc_copyin' - Allocate device memory and copy host memory to it.
======================================================================

_Description_
     In C/C++, this function allocates LEN bytes of device memory and
     maps it to the specified host address in A. The device address of
     the newly allocated device memory is returned.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies a
     variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `void *acc_copyin(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `subroutine acc_copyin(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_copyin(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.17.


File: libgomp.info,  Node: acc_present_or_copyin,  Next: acc_create,  Prev: acc_copyin,  Up: OpenACC Runtime Library Routines

5.18 `acc_present_or_copyin' - If the data is not present on the device, allocate device memory and copy from host memory.
==========================================================================================================================

_Description_
     This function tests if the host data specifed by A and of length
     LEN is present or not. If it is not present, then device memory
     will be allocated and the host memory copied. The device address of
     the newly allocated device memory is returned.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `void *acc_present_or_copyin(h_void *a, size_t len);'
     _Prototype_:  `void *acc_pcopyin(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `subroutine acc_present_or_copyin(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_present_or_copyin(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'
     _Interface_:  `subroutine acc_pcopyin(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_pcopyin(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.18.


File: libgomp.info,  Node: acc_create,  Next: acc_present_or_create,  Prev: acc_present_or_copyin,  Up: OpenACC Runtime Library Routines

5.19 `acc_create' - Allocate device memory and map it to host memory.
=====================================================================

_Description_
     This function allocates device memory and maps it to host memory
     specified by the host address A with a length of LEN bytes. In
     C/C++, the function returns the device address of the allocated
     device memory.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `void *acc_create(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `subroutine acc_create(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_create(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.19.


File: libgomp.info,  Node: acc_present_or_create,  Next: acc_copyout,  Prev: acc_create,  Up: OpenACC Runtime Library Routines

5.20 `acc_present_or_create' - If the data is not present on the device, allocate device memory and map it to host memory.
==========================================================================================================================

_Description_
     This function tests if the host data specifed by A and of length
     LEN is present or not. If it is not present, then device memory
     will be allocated and mapped to host memory. In C/C++, the device
     address of the newly allocated device memory is returned.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `void *acc_present_or_create(h_void *a, size_t len)'
     _Prototype_:  `void *acc_pcreate(h_void *a, size_t len)'

_Fortran_:
     _Interface_:  `subroutine acc_present_or_create(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_present_or_create(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'
     _Interface_:  `subroutine acc_pcreate(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_pcreate(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.20.


File: libgomp.info,  Node: acc_copyout,  Next: acc_delete,  Prev: acc_present_or_create,  Up: OpenACC Runtime Library Routines

5.21 `acc_copyout' - Copy device memory to host memory.
=======================================================

_Description_
     This function copies mapped device memory to host memory which is
     specified by host address A for a length LEN bytes in C/C++.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `acc_copyout(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `subroutine acc_copyout(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_copyout(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.21.


File: libgomp.info,  Node: acc_delete,  Next: acc_update_device,  Prev: acc_copyout,  Up: OpenACC Runtime Library Routines

5.22 `acc_delete' - Free device memory.
=======================================

_Description_
     This function frees previously allocated device memory specified by
     the device address A and the length of LEN bytes.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `acc_delete(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `subroutine acc_delete(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_delete(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.22.


File: libgomp.info,  Node: acc_update_device,  Next: acc_update_self,  Prev: acc_delete,  Up: OpenACC Runtime Library Routines

5.23 `acc_update_device' - Update device memory from mapped host memory.
========================================================================

_Description_
     This function updates the device copy from the previously mapped
     host memory.  The host memory is specified with the host address A
     and a length of LEN bytes.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `acc_update_device(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `subroutine acc_update_device(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_update_device(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.23.


File: libgomp.info,  Node: acc_update_self,  Next: acc_map_data,  Prev: acc_update_device,  Up: OpenACC Runtime Library Routines

5.24 `acc_update_self' - Update host memory from mapped device memory.
======================================================================

_Description_
     This function updates the host copy from the previously mapped
     device memory.  The host memory is specified with the host address
     A and a length of LEN bytes.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.

_C/C++_:
     _Prototype_:  `acc_update_self(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `subroutine acc_update_self(a)'
                   `type, dimension(:[,:]...) :: a'
     _Interface_:  `subroutine acc_update_self(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.24.


File: libgomp.info,  Node: acc_map_data,  Next: acc_unmap_data,  Prev: acc_update_self,  Up: OpenACC Runtime Library Routines

5.25 `acc_map_data' - Map previously allocated device memory to host memory.
============================================================================

_Description_
     This function maps previously allocated device and host memory.
     The device memory is specified with the device address D. The host
     memory is specified with the host address H and a length of LEN.

_C/C++_:
     _Prototype_:  `acc_map_data(h_void *h, d_void *d, size_t len);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.25.


File: libgomp.info,  Node: acc_unmap_data,  Next: acc_deviceptr,  Prev: acc_map_data,  Up: OpenACC Runtime Library Routines

5.26 `acc_unmap_data' - Unmap device memory from host memory.
=============================================================

_Description_
     This function unmaps previously mapped device and host memory. The
     latter specified by H.

_C/C++_:
     _Prototype_:  `acc_unmap_data(h_void *h);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.26.


File: libgomp.info,  Node: acc_deviceptr,  Next: acc_hostptr,  Prev: acc_unmap_data,  Up: OpenACC Runtime Library Routines

5.27 `acc_deviceptr' - Get device pointer associated with specific host address.
================================================================================

_Description_
     This function returns the device address that has been mapped to
     the host address specified by H.

_C/C++_:
     _Prototype_:  `void *acc_deviceptr(h_void *h);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.27.


File: libgomp.info,  Node: acc_hostptr,  Next: acc_is_present,  Prev: acc_deviceptr,  Up: OpenACC Runtime Library Routines

5.28 `acc_hostptr' - Get host pointer associated with specific device address.
==============================================================================

_Description_
     This function returns the host address that has been mapped to the
     device address specified by D.

_C/C++_:
     _Prototype_:  `void *acc_hostptr(d_void *d);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.28.


File: libgomp.info,  Node: acc_is_present,  Next: acc_memcpy_to_device,  Prev: acc_hostptr,  Up: OpenACC Runtime Library Routines

5.29 `acc_is_present' - Indicate whether host variable / array is present on device.
====================================================================================

_Description_
     This function indicates whether the specified host address in A
     and a length of LEN bytes is present on the device. In C/C++, a
     non-zero value is returned to indicate the presence of the mapped
     memory on the device. A zero is returned to indicate the memory is
     not mapped on the device.

     In Fortran, two (2) forms are supported. In the first form, A
     specifies a contiguous array section. The second form A specifies
     a variable or array element and LEN specifies the length in bytes.
     If the host memory is mapped to device memory, then a `true' is
     returned. Otherwise, a `false' is return to indicate the mapped
     memory is not present.

_C/C++_:
     _Prototype_:  `int acc_is_present(h_void *a, size_t len);'

_Fortran_:
     _Interface_:  `function acc_is_present(a)'
                   `type, dimension(:[,:]...) :: a'
                   `logical acc_is_present'
     _Interface_:  `function acc_is_present(a, len)'
                   `type, dimension(:[,:]...) :: a'
                   `integer len'
                   `logical acc_is_present'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.29.


File: libgomp.info,  Node: acc_memcpy_to_device,  Next: acc_memcpy_from_device,  Prev: acc_is_present,  Up: OpenACC Runtime Library Routines

5.30 `acc_memcpy_to_device' - Copy host memory to device memory.
================================================================

_Description_
     This function copies host memory specified by host address of SRC
     to device memory specified by the device address DEST for a length
     of BYTES bytes.

_C/C++_:
     _Prototype_:  `acc_memcpy_to_device(d_void *dest, h_void *src,
                   size_t bytes);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.30.


File: libgomp.info,  Node: acc_memcpy_from_device,  Next: acc_get_current_cuda_device,  Prev: acc_memcpy_to_device,  Up: OpenACC Runtime Library Routines

5.31 `acc_memcpy_from_device' - Copy device memory to host memory.
==================================================================

_Description_
     This function copies host memory specified by host address of SRC
     from device memory specified by the device address DEST for a
     length of BYTES bytes.

_C/C++_:
     _Prototype_:  `acc_memcpy_from_device(d_void *dest, h_void *src,
                   size_t bytes);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     3.2.31.


File: libgomp.info,  Node: acc_get_current_cuda_device,  Next: acc_get_current_cuda_context,  Prev: acc_memcpy_from_device,  Up: OpenACC Runtime Library Routines

5.32 `acc_get_current_cuda_device' - Get CUDA device handle.
============================================================

_Description_
     This function returns the CUDA device handle. This handle is the
     same as used by the CUDA Runtime or Driver API's.

_C/C++_:
     _Prototype_:  `void *acc_get_current_cuda_device(void);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     A.2.1.1.


File: libgomp.info,  Node: acc_get_current_cuda_context,  Next: acc_get_cuda_stream,  Prev: acc_get_current_cuda_device,  Up: OpenACC Runtime Library Routines

5.33 `acc_get_current_cuda_context' - Get CUDA context handle.
==============================================================

_Description_
     This function returns the CUDA context handle. This handle is the
     same as used by the CUDA Runtime or Driver API's.

_C/C++_:
     _Prototype_:  `void *acc_get_current_cuda_context(void);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     A.2.1.2.


File: libgomp.info,  Node: acc_get_cuda_stream,  Next: acc_set_cuda_stream,  Prev: acc_get_current_cuda_context,  Up: OpenACC Runtime Library Routines

5.34 `acc_get_cuda_stream' - Get CUDA stream handle.
====================================================

_Description_
     This function returns the CUDA stream handle for the queue ASYNC.
     This handle is the same as used by the CUDA Runtime or Driver
     API's.

_C/C++_:
     _Prototype_:  `void *acc_get_cuda_stream(int async);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     A.2.1.3.


File: libgomp.info,  Node: acc_set_cuda_stream,  Prev: acc_get_cuda_stream,  Up: OpenACC Runtime Library Routines

5.35 `acc_set_cuda_stream' - Set CUDA stream handle.
====================================================

_Description_
     This function associates the stream handle specified by STREAM with
     the queue ASYNC.

     This cannot be used to change the stream handle associated with
     `acc_async_sync'.

     The return value is not specified.

_C/C++_:
     _Prototype_:  `int acc_set_cuda_stream(int async, void *stream);'

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section
     A.2.1.4.


File: libgomp.info,  Node: OpenACC Environment Variables,  Next: CUDA Streams Usage,  Prev: OpenACC Runtime Library Routines,  Up: Top

6 OpenACC Environment Variables
*******************************

The variables `ACC_DEVICE_TYPE' and `ACC_DEVICE_NUM' are defined by
section 4 of the OpenACC specification in version 2.0.  The variable
`GCC_ACC_NOTIFY' is used for diagnostic purposes.

* Menu:

* ACC_DEVICE_TYPE::
* ACC_DEVICE_NUM::
* GCC_ACC_NOTIFY::


File: libgomp.info,  Node: ACC_DEVICE_TYPE,  Next: ACC_DEVICE_NUM,  Up: OpenACC Environment Variables

6.1 `ACC_DEVICE_TYPE'
=====================

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section 4.1.


File: libgomp.info,  Node: ACC_DEVICE_NUM,  Next: GCC_ACC_NOTIFY,  Prev: ACC_DEVICE_TYPE,  Up: OpenACC Environment Variables

6.2 `ACC_DEVICE_NUM'
====================

_Reference_:
     OpenACC specification v2.0 (https://www.openacc.org), section 4.2.


File: libgomp.info,  Node: GCC_ACC_NOTIFY,  Prev: ACC_DEVICE_NUM,  Up: OpenACC Environment Variables

6.3 `GCC_ACC_NOTIFY'
====================

_Description_:
     Print debug information pertaining to the accelerator.


File: libgomp.info,  Node: CUDA Streams Usage,  Next: OpenACC Library Interoperability,  Prev: OpenACC Environment Variables,  Up: Top

7 CUDA Streams Usage
********************

This applies to the `nvptx' plugin only.

   The library provides elements that perform asynchronous movement of
data and asynchronous operation of computing constructs.  This
asynchronous functionality is implemented by making use of CUDA
streams(1).

   The primary means by that the asychronous functionality is accessed
is through the use of those OpenACC directives which make use of the
`async' and `wait' clauses.  When the `async' clause is first used with
a directive, it creates a CUDA stream.  If an `async-argument' is used
with the `async' clause, then the stream is associated with the
specified `async-argument'.

   Following the creation of an association between a CUDA stream and
the `async-argument' of an `async' clause, both the `wait' clause and
the `wait' directive can be used.  When either the clause or directive
is used after stream creation, it creates a rendezvous point whereby
execution waits until all operations associated with the
`async-argument', that is, stream, have completed.

   Normally, the management of the streams that are created as a result
of using the `async' clause, is done without any intervention by the
caller.  This implies the association between the `async-argument' and
the CUDA stream will be maintained for the lifetime of the program.
However, this association can be changed through the use of the library
function `acc_set_cuda_stream'.  When the function
`acc_set_cuda_stream' is called, the CUDA stream that was originally
associated with the `async' clause will be destroyed.  Caution should
be taken when changing the association as subsequent references to the
`async-argument' refer to a different CUDA stream.

   ---------- Footnotes ----------

   (1) See "Stream Management" in "CUDA Driver API", TRM-06703-001,
Version 5.5, for additional information


File: libgomp.info,  Node: OpenACC Library Interoperability,  Next: The libgomp ABI,  Prev: CUDA Streams Usage,  Up: Top

8 OpenACC Library Interoperability
**********************************

8.1 Introduction
================

The OpenACC library uses the CUDA Driver API, and may interact with
programs that use the Runtime library directly, or another library
based on the Runtime library, e.g., CUBLAS(1).  This chapter describes
the use cases and what changes are required in order to use both the
OpenACC library and the CUBLAS and Runtime libraries within a program.

8.2 First invocation: NVIDIA CUBLAS library API
===============================================

In this first use case (see below), a function in the CUBLAS library is
called prior to any of the functions in the OpenACC library. More
specifically, the function `cublasCreate()'.

   When invoked, the function initializes the library and allocates the
hardware resources on the host and the device on behalf of the caller.
Once the initialization and allocation has completed, a handle is
returned to the caller. The OpenACC library also requires
initialization and allocation of hardware resources. Since the CUBLAS
library has already allocated the hardware resources for the device,
all that is left to do is to initialize the OpenACC library and acquire
the hardware resources on the host.

   Prior to calling the OpenACC function that initializes the library
and allocate the host hardware resources, you need to acquire the
device number that was allocated during the call to `cublasCreate()'.
The invoking of the runtime library function `cudaGetDevice()'
accomplishes this. Once acquired, the device number is passed along
with the device type as parameters to the OpenACC library function
`acc_set_device_num()'.

   Once the call to `acc_set_device_num()' has completed, the OpenACC
library uses the  context that was created during the call to
`cublasCreate()'. In other words, both libraries will be sharing the
same context.

         /* Create the handle */
         s = cublasCreate(&h);
         if (s != CUBLAS_STATUS_SUCCESS)
         {
             fprintf(stderr, "cublasCreate failed %d\n", s);
             exit(EXIT_FAILURE);
         }

         /* Get the device number */
         e = cudaGetDevice(&dev);
         if (e != cudaSuccess)
         {
             fprintf(stderr, "cudaGetDevice failed %d\n", e);
             exit(EXIT_FAILURE);
         }

         /* Initialize OpenACC library and use device 'dev' */
         acc_set_device_num(dev, acc_device_nvidia);
                                 Use Case 1

8.3 First invocation: OpenACC library API
=========================================

In this second use case (see below), a function in the OpenACC library
is called prior to any of the functions in the CUBLAS library. More
specificially, the function `acc_set_device_num()'.

   In the use case presented here, the function `acc_set_device_num()'
is used to both initialize the OpenACC library and allocate the hardware
resources on the host and the device. In the call to the function, the
call parameters specify which device to use and what device type to
use, i.e., `acc_device_nvidia'. It should be noted that this is but one
method to initialize the OpenACC library and allocate the appropriate
hardware resources. Other methods are available through the use of
environment variables and these will be discussed in the next section.

   Once the call to `acc_set_device_num()' has completed, other OpenACC
functions can be called as seen with multiple calls being made to
`acc_copyin()'. In addition, calls can be made to functions in the
CUBLAS library. In the use case a call to `cublasCreate()' is made
subsequent to the calls to `acc_copyin()'.  As seen in the previous use
case, a call to `cublasCreate()' initializes the CUBLAS library and
allocates the hardware resources on the host and the device.  However,
since the device has already been allocated, `cublasCreate()' will only
initialize the CUBLAS library and allocate the appropriate hardware
resources on the host. The context that was created as part of the
OpenACC initialization is shared with the CUBLAS library, similarly to
the first use case.

         dev = 0;

         acc_set_device_num(dev, acc_device_nvidia);

         /* Copy the first set to the device */
         d_X = acc_copyin(&h_X[0], N * sizeof (float));
         if (d_X == NULL)
         {
             fprintf(stderr, "copyin error h_X\n");
             exit(EXIT_FAILURE);
         }

         /* Copy the second set to the device */
         d_Y = acc_copyin(&h_Y1[0], N * sizeof (float));
         if (d_Y == NULL)
         {
             fprintf(stderr, "copyin error h_Y1\n");
             exit(EXIT_FAILURE);
         }

         /* Create the handle */
         s = cublasCreate(&h);
         if (s != CUBLAS_STATUS_SUCCESS)
         {
             fprintf(stderr, "cublasCreate failed %d\n", s);
             exit(EXIT_FAILURE);
         }

         /* Perform saxpy using CUBLAS library function */
         s = cublasSaxpy(h, N, &alpha, d_X, 1, d_Y, 1);
         if (s != CUBLAS_STATUS_SUCCESS)
         {
             fprintf(stderr, "cublasSaxpy failed %d\n", s);
             exit(EXIT_FAILURE);
         }

         /* Copy the results from the device */
         acc_memcpy_from_device(&h_Y1[0], d_Y, N * sizeof (float));
                                 Use Case 2

8.4 OpenACC library and environment variables
=============================================

There are two environment variables associated with the OpenACC library
that may be used to control the device type and device number:
`ACC_DEVICE_TYPE' and `ACC_DEVICE_NUM', respecively. These two
environement variables can be used as an alternative to calling
`acc_set_device_num()'. As seen in the second use case, the device type
and device number were specified using `acc_set_device_num()'.  If
however, the aforementioned environment variables were set, then the
call to `acc_set_device_num()' would not be required.

   The use of the environment variables is only relevant when an
OpenACC function is called prior to a call to `cudaCreate()'. If
`cudaCreate()' is called prior to a call to an OpenACC function, then
you must call `acc_set_device_num()'(2)

   ---------- Footnotes ----------

   (1) See section 2.26, "Interactions with the CUDA Driver API" in
"CUDA Runtime API", Version 5.5, and section 2.27, "VDPAU
Interoperability", in "CUDA Driver API", TRM-06703-001, Version 5.5,
for additional information on library interoperability.

   (2) More complete information about `ACC_DEVICE_TYPE' and
`ACC_DEVICE_NUM' can be found in sections 4.1 and 4.2 of the OpenACC
(https://www.openacc.org) Application Programming Interface”, Version
2.0.


File: libgomp.info,  Node: The libgomp ABI,  Next: Reporting Bugs,  Prev: OpenACC Library Interoperability,  Up: Top

9 The libgomp ABI
*****************

The following sections present notes on the external ABI as presented
by libgomp.  Only maintainers should need them.

* Menu:

* Implementing MASTER construct::
* Implementing CRITICAL construct::
* Implementing ATOMIC construct::
* Implementing FLUSH construct::
* Implementing BARRIER construct::
* Implementing THREADPRIVATE construct::
* Implementing PRIVATE clause::
* Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses::
* Implementing REDUCTION clause::
* Implementing PARALLEL construct::
* Implementing FOR construct::
* Implementing ORDERED construct::
* Implementing SECTIONS construct::
* Implementing SINGLE construct::
* Implementing OpenACC's PARALLEL construct::


File: libgomp.info,  Node: Implementing MASTER construct,  Next: Implementing CRITICAL construct,  Up: The libgomp ABI

9.1 Implementing MASTER construct
=================================

     if (omp_get_thread_num () == 0)
       block

   Alternately, we generate two copies of the parallel subfunction and
only include this in the version run by the master thread.  Surely this
is not worthwhile though...


File: libgomp.info,  Node: Implementing CRITICAL construct,  Next: Implementing ATOMIC construct,  Prev: Implementing MASTER construct,  Up: The libgomp ABI

9.2 Implementing CRITICAL construct
===================================

Without a specified name,

       void GOMP_critical_start (void);
       void GOMP_critical_end (void);

   so that we don't get COPY relocations from libgomp to the main
application.

   With a specified name, use omp_set_lock and omp_unset_lock with name
being transformed into a variable declared like

       omp_lock_t gomp_critical_user_<name> __attribute__((common))

   Ideally the ABI would specify that all zero is a valid unlocked
state, and so we wouldn't need to initialize this at startup.


File: libgomp.info,  Node: Implementing ATOMIC construct,  Next: Implementing FLUSH construct,  Prev: Implementing CRITICAL construct,  Up: The libgomp ABI

9.3 Implementing ATOMIC construct
=================================

The target should implement the `__sync' builtins.

   Failing that we could add

       void GOMP_atomic_enter (void)
       void GOMP_atomic_exit (void)

   which reuses the regular lock code, but with yet another lock object
private to the library.


File: libgomp.info,  Node: Implementing FLUSH construct,  Next: Implementing BARRIER construct,  Prev: Implementing ATOMIC construct,  Up: The libgomp ABI

9.4 Implementing FLUSH construct
================================

Expands to the `__sync_synchronize' builtin.


File: libgomp.info,  Node: Implementing BARRIER construct,  Next: Implementing THREADPRIVATE construct,  Prev: Implementing FLUSH construct,  Up: The libgomp ABI

9.5 Implementing BARRIER construct
==================================

       void GOMP_barrier (void)


File: libgomp.info,  Node: Implementing THREADPRIVATE construct,  Next: Implementing PRIVATE clause,  Prev: Implementing BARRIER construct,  Up: The libgomp ABI

9.6 Implementing THREADPRIVATE construct
========================================

In _most_ cases we can map this directly to `__thread'.  Except that
OMP allows constructors for C++ objects.  We can either refuse to
support this (how often is it used?) or we can implement something akin
to .ctors.

   Even more ideally, this ctor feature is handled by extensions to the
main pthreads library.  Failing that, we can have a set of entry points
to register ctor functions to be called.


File: libgomp.info,  Node: Implementing PRIVATE clause,  Next: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses,  Prev: Implementing THREADPRIVATE construct,  Up: The libgomp ABI

9.7 Implementing PRIVATE clause
===============================

In association with a PARALLEL, or within the lexical extent of a
PARALLEL block, the variable becomes a local variable in the parallel
subfunction.

   In association with FOR or SECTIONS blocks, create a new automatic
variable within the current function.  This preserves the semantic of
new variable creation.


File: libgomp.info,  Node: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses,  Next: Implementing REDUCTION clause,  Prev: Implementing PRIVATE clause,  Up: The libgomp ABI

9.8 Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses
========================================================================

This seems simple enough for PARALLEL blocks.  Create a private struct
for communicating between the parent and subfunction.  In the parent,
copy in values for scalar and "small" structs; copy in addresses for
others TREE_ADDRESSABLE types.  In the subfunction, copy the value into
the local variable.

   It is not clear what to do with bare FOR or SECTION blocks.  The
only thing I can figure is that we do something like:

     #pragma omp for firstprivate(x) lastprivate(y)
     for (int i = 0; i < n; ++i)
       body;

   which becomes

     {
       int x = x, y;

       // for stuff

       if (i == n)
         y = y;
     }

   where the "x=x" and "y=y" assignments actually have different uids
for the two variables, i.e. not something you could write directly in
C.  Presumably this only makes sense if the "outer" x and y are global
variables.

   COPYPRIVATE would work the same way, except the structure broadcast
would have to happen via SINGLE machinery instead.


File: libgomp.info,  Node: Implementing REDUCTION clause,  Next: Implementing PARALLEL construct,  Prev: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses,  Up: The libgomp ABI

9.9 Implementing REDUCTION clause
=================================

The private struct mentioned in the previous section should have a
pointer to an array of the type of the variable, indexed by the
thread's TEAM_ID.  The thread stores its final value into the array,
and after the barrier, the master thread iterates over the array to
collect the values.


File: libgomp.info,  Node: Implementing PARALLEL construct,  Next: Implementing FOR construct,  Prev: Implementing REDUCTION clause,  Up: The libgomp ABI

9.10 Implementing PARALLEL construct
====================================

       #pragma omp parallel
       {
         body;
       }

   becomes

       void subfunction (void *data)
       {
         use data;
         body;
       }

       setup data;
       GOMP_parallel_start (subfunction, &data, num_threads);
       subfunction (&data);
       GOMP_parallel_end ();

       void GOMP_parallel_start (void (*fn)(void *), void *data, unsigned num_threads)

   The FN argument is the subfunction to be run in parallel.

   The DATA argument is a pointer to a structure used to communicate
data in and out of the subfunction, as discussed above with respect to
FIRSTPRIVATE et al.

   The NUM_THREADS argument is 1 if an IF clause is present and false,
or the value of the NUM_THREADS clause, if present, or 0.

   The function needs to create the appropriate number of threads
and/or launch them from the dock.  It needs to create the team
structure and assign team ids.

       void GOMP_parallel_end (void)

   Tears down the team and returns us to the previous
`omp_in_parallel()' state.


File: libgomp.info,  Node: Implementing FOR construct,  Next: Implementing ORDERED construct,  Prev: Implementing PARALLEL construct,  Up: The libgomp ABI

9.11 Implementing FOR construct
===============================

       #pragma omp parallel for
       for (i = lb; i <= ub; i++)
         body;

   becomes

       void subfunction (void *data)
       {
         long _s0, _e0;
         while (GOMP_loop_static_next (&_s0, &_e0))
         {
           long _e1 = _e0, i;
           for (i = _s0; i < _e1; i++)
             body;
         }
         GOMP_loop_end_nowait ();
       }

       GOMP_parallel_loop_static (subfunction, NULL, 0, lb, ub+1, 1, 0);
       subfunction (NULL);
       GOMP_parallel_end ();

       #pragma omp for schedule(runtime)
       for (i = 0; i < n; i++)
         body;

   becomes

       {
         long i, _s0, _e0;
         if (GOMP_loop_runtime_start (0, n, 1, &_s0, &_e0))
           do {
             long _e1 = _e0;
             for (i = _s0, i < _e0; i++)
               body;
           } while (GOMP_loop_runtime_next (&_s0, _&e0));
         GOMP_loop_end ();
       }

   Note that while it looks like there is trickiness to propagating a
non-constant STEP, there isn't really.  We're explicitly allowed to
evaluate it as many times as we want, and any variables involved should
automatically be handled as PRIVATE or SHARED like any other variables.
So the expression should remain evaluable in the subfunction.  We can
also pull it into a local variable if we like, but since its supposed
to remain unchanged, we can also not if we like.

   If we have SCHEDULE(STATIC), and no ORDERED, then we ought to be
able to get away with no work-sharing context at all, since we can
simply perform the arithmetic directly in each thread to divide up the
iterations.  Which would mean that we wouldn't need to call any of
these routines.

   There are separate routines for handling loops with an ORDERED
clause.  Bookkeeping for that is non-trivial...


File: libgomp.info,  Node: Implementing ORDERED construct,  Next: Implementing SECTIONS construct,  Prev: Implementing FOR construct,  Up: The libgomp ABI

9.12 Implementing ORDERED construct
===================================

       void GOMP_ordered_start (void)
       void GOMP_ordered_end (void)


File: libgomp.info,  Node: Implementing SECTIONS construct,  Next: Implementing SINGLE construct,  Prev: Implementing ORDERED construct,  Up: The libgomp ABI

9.13 Implementing SECTIONS construct
====================================

A block as

       #pragma omp sections
       {
         #pragma omp section
         stmt1;
         #pragma omp section
         stmt2;
         #pragma omp section
         stmt3;
       }

   becomes

       for (i = GOMP_sections_start (3); i != 0; i = GOMP_sections_next ())
         switch (i)
           {
           case 1:
             stmt1;
             break;
           case 2:
             stmt2;
             break;
           case 3:
             stmt3;
             break;
           }
       GOMP_barrier ();


File: libgomp.info,  Node: Implementing SINGLE construct,  Next: Implementing OpenACC's PARALLEL construct,  Prev: Implementing SECTIONS construct,  Up: The libgomp ABI

9.14 Implementing SINGLE construct
==================================

A block like

       #pragma omp single
       {
         body;
       }

   becomes

       if (GOMP_single_start ())
         body;
       GOMP_barrier ();

   while

       #pragma omp single copyprivate(x)
         body;

   becomes

       datap = GOMP_single_copy_start ();
       if (datap == NULL)
         {
           body;
           data.x = x;
           GOMP_single_copy_end (&data);
         }
       else
         x = datap->x;
       GOMP_barrier ();


File: libgomp.info,  Node: Implementing OpenACC's PARALLEL construct,  Prev: Implementing SINGLE construct,  Up: The libgomp ABI

9.15 Implementing OpenACC's PARALLEL construct
==============================================

       void GOACC_parallel ()


File: libgomp.info,  Node: Reporting Bugs,  Next: Copying,  Prev: The libgomp ABI,  Up: Top

10 Reporting Bugs
*****************

Bugs in the GNU Offloading and Multi Processing Runtime Library should
be reported via Bugzilla (http://gcc.gnu.org/bugzilla/).  Please add
"openacc", or "openmp", or both to the keywords field in the bug
report, as appropriate.


File: libgomp.info,  Node: Copying,  Next: GNU Free Documentation License,  Prev: Reporting Bugs,  Up: Top

GNU General Public License
**************************

                        Version 3, 29 June 2007

     Copyright (C) 2007 Free Software Foundation, Inc. `http://fsf.org/'

     Everyone is permitted to copy and distribute verbatim copies of this
     license document, but changing it is not allowed.

Preamble
========

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   To protect your rights, we need to prevent others from denying you
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   Developers that use the GNU GPL protect your rights with two steps:
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     You may not propagate or modify a covered work except as expressly
     provided under this License.  Any attempt otherwise to propagate or
     modify it is void, and will automatically terminate your rights
     under this License (including any patent licenses granted under
     the third paragraph of section 11).

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly
     and finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from
     you under this License.  If your rights have been terminated and
     not permanently reinstated, you do not qualify to receive new
     licenses for the same material under section 10.

  9. Acceptance Not Required for Having Copies.

     You are not required to accept this License in order to receive or
     run a copy of the Program.  Ancillary propagation of a covered work
     occurring solely as a consequence of using peer-to-peer
     transmission to receive a copy likewise does not require
     acceptance.  However, nothing other than this License grants you
     permission to propagate or modify any covered work.  These actions
     infringe copyright if you do not accept this License.  Therefore,
     by modifying or propagating a covered work, you indicate your
     acceptance of this License to do so.

 10. Automatic Licensing of Downstream Recipients.

     Each time you convey a covered work, the recipient automatically
     receives a license from the original licensors, to run, modify and
     propagate that work, subject to this License.  You are not
     responsible for enforcing compliance by third parties with this
     License.

     An "entity transaction" is a transaction transferring control of an
     organization, or substantially all assets of one, or subdividing an
     organization, or merging organizations.  If propagation of a
     covered work results from an entity transaction, each party to that
     transaction who receives a copy of the work also receives whatever
     licenses to the work the party's predecessor in interest had or
     could give under the previous paragraph, plus a right to
     possession of the Corresponding Source of the work from the
     predecessor in interest, if the predecessor has it or can get it
     with reasonable efforts.

     You may not impose any further restrictions on the exercise of the
     rights granted or affirmed under this License.  For example, you
     may not impose a license fee, royalty, or other charge for
     exercise of rights granted under this License, and you may not
     initiate litigation (including a cross-claim or counterclaim in a
     lawsuit) alleging that any patent claim is infringed by making,
     using, selling, offering for sale, or importing the Program or any
     portion of it.

 11. Patents.

     A "contributor" is a copyright holder who authorizes use under this
     License of the Program or a work on which the Program is based.
     The work thus licensed is called the contributor's "contributor
     version".

     A contributor's "essential patent claims" are all patent claims
     owned or controlled by the contributor, whether already acquired or
     hereafter acquired, that would be infringed by some manner,
     permitted by this License, of making, using, or selling its
     contributor version, but do not include claims that would be
     infringed only as a consequence of further modification of the
     contributor version.  For purposes of this definition, "control"
     includes the right to grant patent sublicenses in a manner
     consistent with the requirements of this License.

     Each contributor grants you a non-exclusive, worldwide,
     royalty-free patent license under the contributor's essential
     patent claims, to make, use, sell, offer for sale, import and
     otherwise run, modify and propagate the contents of its
     contributor version.

     In the following three paragraphs, a "patent license" is any
     express agreement or commitment, however denominated, not to
     enforce a patent (such as an express permission to practice a
     patent or covenant not to sue for patent infringement).  To
     "grant" such a patent license to a party means to make such an
     agreement or commitment not to enforce a patent against the party.

     If you convey a covered work, knowingly relying on a patent
     license, and the Corresponding Source of the work is not available
     for anyone to copy, free of charge and under the terms of this
     License, through a publicly available network server or other
     readily accessible means, then you must either (1) cause the
     Corresponding Source to be so available, or (2) arrange to deprive
     yourself of the benefit of the patent license for this particular
     work, or (3) arrange, in a manner consistent with the requirements
     of this License, to extend the patent license to downstream
     recipients.  "Knowingly relying" means you have actual knowledge
     that, but for the patent license, your conveying the covered work
     in a country, or your recipient's use of the covered work in a
     country, would infringe one or more identifiable patents in that
     country that you have reason to believe are valid.

     If, pursuant to or in connection with a single transaction or
     arrangement, you convey, or propagate by procuring conveyance of, a
     covered work, and grant a patent license to some of the parties
     receiving the covered work authorizing them to use, propagate,
     modify or convey a specific copy of the covered work, then the
     patent license you grant is automatically extended to all
     recipients of the covered work and works based on it.

     A patent license is "discriminatory" if it does not include within
     the scope of its coverage, prohibits the exercise of, or is
     conditioned on the non-exercise of one or more of the rights that
     are specifically granted under this License.  You may not convey a
     covered work if you are a party to an arrangement with a third
     party that is in the business of distributing software, under
     which you make payment to the third party based on the extent of
     your activity of conveying the work, and under which the third
     party grants, to any of the parties who would receive the covered
     work from you, a discriminatory patent license (a) in connection
     with copies of the covered work conveyed by you (or copies made
     from those copies), or (b) primarily for and in connection with
     specific products or compilations that contain the covered work,
     unless you entered into that arrangement, or that patent license
     was granted, prior to 28 March 2007.

     Nothing in this License shall be construed as excluding or limiting
     any implied license or other defenses to infringement that may
     otherwise be available to you under applicable patent law.

 12. No Surrender of Others' Freedom.

     If conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot convey a covered work so as to satisfy
     simultaneously your obligations under this License and any other
     pertinent obligations, then as a consequence you may not convey it
     at all.  For example, if you agree to terms that obligate you to
     collect a royalty for further conveying from those to whom you
     convey the Program, the only way you could satisfy both those
     terms and this License would be to refrain entirely from conveying
     the Program.

 13. Use with the GNU Affero General Public License.

     Notwithstanding any other provision of this License, you have
     permission to link or combine any covered work with a work licensed
     under version 3 of the GNU Affero General Public License into a
     single combined work, and to convey the resulting work.  The terms
     of this License will continue to apply to the part which is the
     covered work, but the special requirements of the GNU Affero
     General Public License, section 13, concerning interaction through
     a network will apply to the combination as such.

 14. Revised Versions of this License.

     The Free Software Foundation may publish revised and/or new
     versions of the GNU General Public License from time to time.
     Such new versions will be similar in spirit to the present
     version, but may differ in detail to address new problems or
     concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies that a certain numbered version of the GNU
     General Public License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that numbered version or of any later version published by the
     Free Software Foundation.  If the Program does not specify a
     version number of the GNU General Public License, you may choose
     any version ever published by the Free Software Foundation.

     If the Program specifies that a proxy can decide which future
     versions of the GNU General Public License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Program.

     Later license versions may give you additional or different
     permissions.  However, no additional obligations are imposed on any
     author or copyright holder as a result of your choosing to follow a
     later version.

 15. Disclaimer of Warranty.

     THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
     APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE
     COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
     WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE
     RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.
     SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
     NECESSARY SERVICING, REPAIR OR CORRECTION.

 16. Limitation of Liability.

     IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
     AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU
     FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
     CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
     THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
     BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
     PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
     PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
     THE POSSIBILITY OF SUCH DAMAGES.

 17. Interpretation of Sections 15 and 16.

     If the disclaimer of warranty and limitation of liability provided
     above cannot be given local legal effect according to their terms,
     reviewing courts shall apply local law that most closely
     approximates an absolute waiver of all civil liability in
     connection with the Program, unless a warranty or assumption of
     liability accompanies a copy of the Program in return for a fee.


END OF TERMS AND CONDITIONS
===========================

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR NAME OF AUTHOR

     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation, either version 3 of the License, or (at
     your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program.  If not, see `http://www.gnu.org/licenses/'.

   Also add information on how to contact you by electronic and paper
mail.

   If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

     PROGRAM Copyright (C) YEAR NAME OF AUTHOR
     This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.

   The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".

   You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  For more information on this, and how to apply and follow
the GNU GPL, see `http://www.gnu.org/licenses/'.

   The GNU General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Lesser General Public License instead of this License.  But first,
please read `http://www.gnu.org/philosophy/why-not-lgpl.html'.


File: libgomp.info,  Node: GNU Free Documentation License,  Next: Funding,  Prev: Copying,  Up: Top

GNU Free Documentation License
******************************

                     Version 1.3, 3 November 2008

     Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     `http://fsf.org/'

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.
     We recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it
     can be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You
     accept the license if you copy, modify or distribute the work in a
     way requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in
     the notice that says that the Document is released under this
     License.  If a section does not fit the above definition of
     Secondary then it is not allowed to be designated as Invariant.
     The Document may contain zero Invariant Sections.  If the Document
     does not identify any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images
     composed of pixels) generic paint programs or (for drawings) some
     widely available drawing editor, and that is suitable for input to
     text formatters or for automatic translation to a variety of
     formats suitable for input to text formatters.  A copy made in an
     otherwise Transparent file format whose markup, or absence of
     markup, has been arranged to thwart or discourage subsequent
     modification by readers is not Transparent.  An image format is
     not Transparent if used for any substantial amount of text.  A
     copy that is not "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and
     standard-conforming simple HTML, PostScript or PDF designed for
     human modification.  Examples of transparent image formats include
     PNG, XCF and JPG.  Opaque formats include proprietary formats that
     can be read and edited only by proprietary word processors, SGML or
     XML for which the DTD and/or processing tools are not generally
     available, and the machine-generated HTML, PostScript or PDF
     produced by some word processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     The "publisher" means any person or entity that distributes copies
     of the Document to the public.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements", "Dedications", "Endorsements", or "History".)
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
     covers, as long as they preserve the title of the Document and
     satisfy these conditions, can be treated as verbatim copying in
     other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy a computer-network location from
     which the general network-using public has access to download
     using public-standard network protocols a complete Transparent
     copy of the Document, free of added material.  If you use the
     latter option, you must take reasonably prudent steps, when you
     begin distribution of Opaque copies in quantity, to ensure that
     this Transparent copy will remain thus accessible at the stated
     location until at least one year after the last time you
     distribute an Opaque copy (directly or through your agents or
     retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of
     copies, to give them a chance to provide you with an updated
     version of the Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with
     the Modified Version filling the role of the Document, thus
     licensing distribution and modification of the Modified Version to
     whoever possesses a copy of it.  In addition, you must do these
     things in the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of
          previous versions (which should, if there were any, be listed
          in the History section of the Document).  You may use the
          same title as a previous version if the original publisher of
          that version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on
          the Title Page.  If there is no section Entitled "History" in
          the Document, create one stating the title, year, authors,
          and publisher of the Document as given on its Title Page,
          then add an item describing the Modified Version as stated in
          the previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
          section all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document,
          unaltered in their text and in their titles.  Section numbers
          or the equivalent are not considered part of the section
          titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option
     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
     passage of Front-Cover Text and one of Back-Cover Text may be
     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
     previously added by you or by arrangement made by the same entity
     you are acting on behalf of, you may not add another; but you may
     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense, or distribute it is void,
     and will automatically terminate your rights under this License.

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly
     and finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from
     you under this License.  If your rights have been terminated and
     not permanently reinstated, receipt of a copy of some or all of
     the same material does not give you any rights to use it.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     `http://www.gnu.org/copyleft/'.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.  If the Document specifies that a proxy
     can decide which future versions of this License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Document.

 11. RELICENSING

     "Massive Multiauthor Collaboration Site" (or "MMC Site") means any
     World Wide Web server that publishes copyrightable works and also
     provides prominent facilities for anybody to edit those works.  A
     public wiki that anybody can edit is an example of such a server.
     A "Massive Multiauthor Collaboration" (or "MMC") contained in the
     site means any set of copyrightable works thus published on the MMC
     site.

     "CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
     license published by Creative Commons Corporation, a not-for-profit
     corporation with a principal place of business in San Francisco,
     California, as well as future copyleft versions of that license
     published by that same organization.

     "Incorporate" means to publish or republish a Document, in whole or
     in part, as part of another Document.

     An MMC is "eligible for relicensing" if it is licensed under this
     License, and if all works that were first published under this
     License somewhere other than this MMC, and subsequently
     incorporated in whole or in part into the MMC, (1) had no cover
     texts or invariant sections, and (2) were thus incorporated prior
     to November 1, 2008.

     The operator of an MMC Site may republish an MMC contained in the
     site under CC-BY-SA on the same site at any time before August 1,
     2009, provided the MMC is eligible for relicensing.


ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


File: libgomp.info,  Node: Funding,  Next: Library Index,  Prev: GNU Free Documentation License,  Up: Top

Funding Free Software
*********************

If you want to have more free software a few years from now, it makes
sense for you to help encourage people to contribute funds for its
development.  The most effective approach known is to encourage
commercial redistributors to donate.

   Users of free software systems can boost the pace of development by
encouraging for-a-fee distributors to donate part of their selling price
to free software developers--the Free Software Foundation, and others.

   The way to convince distributors to do this is to demand it and
expect it from them.  So when you compare distributors, judge them
partly by how much they give to free software development.  Show
distributors they must compete to be the one who gives the most.

   To make this approach work, you must insist on numbers that you can
compare, such as, "We will donate ten dollars to the Frobnitz project
for each disk sold."  Don't be satisfied with a vague promise, such as
"A portion of the profits are donated," since it doesn't give a basis
for comparison.

   Even a precise fraction "of the profits from this disk" is not very
meaningful, since creative accounting and unrelated business decisions
can greatly alter what fraction of the sales price counts as profit.
If the price you pay is $50, ten percent of the profit is probably less
than a dollar; it might be a few cents, or nothing at all.

   Some redistributors do development work themselves.  This is useful
too; but to keep everyone honest, you need to inquire how much they do,
and what kind.  Some kinds of development make much more long-term
difference than others.  For example, maintaining a separate version of
a program contributes very little; maintaining the standard version of a
program for the whole community contributes much.  Easy new ports
contribute little, since someone else would surely do them; difficult
ports such as adding a new CPU to the GNU Compiler Collection
contribute more; major new features or packages contribute the most.

   By establishing the idea that supporting further development is "the
proper thing to do" when distributing free software for a fee, we can
assure a steady flow of resources into making more free software.

     Copyright (C) 1994 Free Software Foundation, Inc.
     Verbatim copying and redistribution of this section is permitted
     without royalty; alteration is not permitted.


File: libgomp.info,  Node: Library Index,  Prev: Funding,  Up: Top

Library Index
*************

 [index ]
* Menu:

* Environment Variable <1>:              GOMP_RTEMS_THREAD_POOLS.
                                                                (line 6)
* Environment Variable <2>:              GOMP_SPINCOUNT.        (line 6)
* Environment Variable <3>:              GOMP_STACKSIZE.        (line 6)
* Environment Variable <4>:              GOMP_DEBUG.            (line 6)
* Environment Variable <5>:              GOMP_CPU_AFFINITY.     (line 6)
* Environment Variable <6>:              OMP_WAIT_POLICY.       (line 6)
* Environment Variable <7>:              OMP_THREAD_LIMIT.      (line 6)
* Environment Variable <8>:              OMP_SCHEDULE.          (line 6)
* Environment Variable <9>:              OMP_STACKSIZE.         (line 6)
* Environment Variable <10>:             OMP_PLACES.            (line 6)
* Environment Variable <11>:             OMP_PROC_BIND.         (line 6)
* Environment Variable <12>:             OMP_NUM_THREADS.       (line 6)
* Environment Variable <13>:             OMP_NESTED.            (line 6)
* Environment Variable <14>:             OMP_MAX_TASK_PRIORITY. (line 6)
* Environment Variable <15>:             OMP_MAX_ACTIVE_LEVELS. (line 6)
* Environment Variable <16>:             OMP_DYNAMIC.           (line 6)
* Environment Variable <17>:             OMP_DEFAULT_DEVICE.    (line 6)
* Environment Variable <18>:             OMP_DISPLAY_ENV.       (line 6)
* Environment Variable:                  OMP_CANCELLATION.      (line 6)
* FDL, GNU Free Documentation License:   GNU Free Documentation License.
                                                                (line 6)
* Implementation specific setting <1>:   GOMP_RTEMS_THREAD_POOLS.
                                                                (line 6)
* Implementation specific setting <2>:   GOMP_SPINCOUNT.        (line 6)
* Implementation specific setting <3>:   GOMP_STACKSIZE.        (line 6)
* Implementation specific setting <4>:   OMP_SCHEDULE.          (line 6)
* Implementation specific setting <5>:   OMP_NUM_THREADS.       (line 6)
* Implementation specific setting:       OMP_NESTED.            (line 6)
* Introduction:                          Top.                   (line 6)



Tag Table:
Node: Top2189
Node: Enabling OpenMP4719
Node: Runtime Library Routines5507
Node: omp_get_active_level8584
Node: omp_get_ancestor_thread_num9282
Node: omp_get_cancellation10209
Node: omp_get_default_device11021
Node: omp_get_dynamic11695
Node: omp_get_level12568
Node: omp_get_max_active_levels13186
Node: omp_get_max_task_priority13889
Node: omp_get_max_threads14507
Node: omp_get_nested15262
Node: omp_get_num_devices16174
Node: omp_get_num_procs16693
Node: omp_get_num_teams17230
Node: omp_get_num_threads17744
Node: omp_get_proc_bind18831
Node: omp_get_schedule19749
Node: omp_get_team_num20698
Node: omp_get_team_size21195
Node: omp_get_thread_limit22152
Node: omp_get_thread_num22769
Node: omp_in_parallel23638
Node: omp_in_final24285
Node: omp_is_initial_device24957
Node: omp_set_default_device25648
Node: omp_set_dynamic26436
Node: omp_set_max_active_levels27319
Node: omp_set_nested28093
Node: omp_set_num_threads28982
Node: omp_set_schedule29847
Node: omp_init_lock30923
Node: omp_set_lock31573
Node: omp_test_lock32425
Node: omp_unset_lock33398
Node: omp_destroy_lock34326
Node: omp_init_nest_lock35000
Node: omp_set_nest_lock35732
Node: omp_test_nest_lock36649
Node: omp_unset_nest_lock37679
Node: omp_destroy_nest_lock38691
Node: omp_get_wtick39439
Node: omp_get_wtime40029
Node: Environment Variables40803
Node: OMP_CANCELLATION42372
Node: OMP_DISPLAY_ENV42905
Node: OMP_DEFAULT_DEVICE43608
Node: OMP_DYNAMIC44388
Node: OMP_MAX_ACTIVE_LEVELS44984
Node: OMP_MAX_TASK_PRIORITY45634
Node: OMP_NESTED46294
Node: OMP_NUM_THREADS46899
Node: OMP_PROC_BIND47588
Node: OMP_PLACES48780
Node: OMP_STACKSIZE50957
Node: OMP_SCHEDULE51781
Node: OMP_THREAD_LIMIT52479
Node: OMP_WAIT_POLICY53079
Node: GOMP_CPU_AFFINITY53771
Node: GOMP_DEBUG55502
Node: GOMP_STACKSIZE56009
Node: GOMP_SPINCOUNT56838
Node: GOMP_RTEMS_THREAD_POOLS58047
Node: Enabling OpenACC60228
Node: OpenACC Runtime Library Routines61222
Node: acc_get_num_devices65016
Node: acc_set_device_type65739
Node: acc_get_device_type66500
Node: acc_set_device_num67212
Node: acc_get_device_num68011
Node: acc_async_test68804
Node: acc_async_test_all69789
Node: acc_wait70684
Node: acc_wait_all71544
Node: acc_wait_all_async72303
Node: acc_wait_async73052
Node: acc_init73756
Node: acc_shutdown74399
Node: acc_on_device75064
Node: acc_malloc76062
Node: acc_free76559
Node: acc_copyin76985
Node: acc_present_or_copyin78086
Node: acc_create79696
Node: acc_present_or_create80842
Node: acc_copyout82460
Node: acc_delete83475
Node: acc_update_device84442
Node: acc_update_self85546
Node: acc_map_data86642
Node: acc_unmap_data87325
Node: acc_deviceptr87844
Node: acc_hostptr88413
Node: acc_is_present88976
Node: acc_memcpy_to_device90490
Node: acc_memcpy_from_device91151
Node: acc_get_current_cuda_device91833
Node: acc_get_current_cuda_context92428
Node: acc_get_cuda_stream93026
Node: acc_set_cuda_stream93616
Node: OpenACC Environment Variables94260
Node: ACC_DEVICE_TYPE94719
Node: ACC_DEVICE_NUM94955
Node: GCC_ACC_NOTIFY95212
Node: CUDA Streams Usage95435
Ref: CUDA Streams Usage-Footnote-197335
Node: OpenACC Library Interoperability97444
Ref: OpenACC Library Interoperability-Footnote-1103790
Ref: OpenACC Library Interoperability-Footnote-2104042
Node: The libgomp ABI104250
Node: Implementing MASTER construct105106
Node: Implementing CRITICAL construct105520
Node: Implementing ATOMIC construct106259
Node: Implementing FLUSH construct106740
Node: Implementing BARRIER construct107011
Node: Implementing THREADPRIVATE construct107280
Node: Implementing PRIVATE clause107932
Node: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses108513
Node: Implementing REDUCTION clause109837
Node: Implementing PARALLEL construct110394
Node: Implementing FOR construct111651
Node: Implementing ORDERED construct113649
Node: Implementing SECTIONS construct113955
Node: Implementing SINGLE construct114721
Node: Implementing OpenACC's PARALLEL construct115433
Node: Reporting Bugs115691
Node: Copying116053
Node: GNU Free Documentation License153618
Node: Funding178760
Node: Library Index181285

End Tag Table