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| <title>Debugging with GDB: Non-Stop Mode</title> |
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| <a name="Non_002dStop-Mode"></a> |
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| Next: <a href="Background-Execution.html#Background-Execution" accesskey="n" rel="next">Background Execution</a>, Previous: <a href="All_002dStop-Mode.html#All_002dStop-Mode" accesskey="p" rel="prev">All-Stop Mode</a>, Up: <a href="Thread-Stops.html#Thread-Stops" accesskey="u" rel="up">Thread Stops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
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| <hr> |
| <a name="Non_002dStop-Mode-1"></a> |
| <h4 class="subsection">5.5.2 Non-Stop Mode</h4> |
| |
| <a name="index-non_002dstop-mode"></a> |
| |
| |
| <p>For some multi-threaded targets, <small>GDB</small> supports an optional |
| mode of operation in which you can examine stopped program threads in |
| the debugger while other threads continue to execute freely. This |
| minimizes intrusion when debugging live systems, such as programs |
| where some threads have real-time constraints or must continue to |
| respond to external events. This is referred to as <em>non-stop</em> mode. |
| </p> |
| <p>In non-stop mode, when a thread stops to report a debugging event, |
| <em>only</em> that thread is stopped; <small>GDB</small> does not stop other |
| threads as well, in contrast to the all-stop mode behavior. Additionally, |
| execution commands such as <code>continue</code> and <code>step</code> apply by default |
| only to the current thread in non-stop mode, rather than all threads as |
| in all-stop mode. This allows you to control threads explicitly in |
| ways that are not possible in all-stop mode — for example, stepping |
| one thread while allowing others to run freely, stepping |
| one thread while holding all others stopped, or stepping several threads |
| independently and simultaneously. |
| </p> |
| <p>To enter non-stop mode, use this sequence of commands before you run |
| or attach to your program: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample"># If using the CLI, pagination breaks non-stop. |
| set pagination off |
| |
| # Finally, turn it on! |
| set non-stop on |
| </pre></div> |
| |
| <p>You can use these commands to manipulate the non-stop mode setting: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-set-non_002dstop"></a> |
| </dd> |
| <dt><code>set non-stop on</code></dt> |
| <dd><p>Enable selection of non-stop mode. |
| </p></dd> |
| <dt><code>set non-stop off</code></dt> |
| <dd><p>Disable selection of non-stop mode. |
| <a name="index-show-non_002dstop"></a> |
| </p></dd> |
| <dt><code>show non-stop</code></dt> |
| <dd><p>Show the current non-stop enablement setting. |
| </p></dd> |
| </dl> |
| |
| <p>Note these commands only reflect whether non-stop mode is enabled, |
| not whether the currently-executing program is being run in non-stop mode. |
| In particular, the <code>set non-stop</code> preference is only consulted when |
| <small>GDB</small> starts or connects to the target program, and it is generally |
| not possible to switch modes once debugging has started. Furthermore, |
| since not all targets support non-stop mode, even when you have enabled |
| non-stop mode, <small>GDB</small> may still fall back to all-stop operation by |
| default. |
| </p> |
| <p>In non-stop mode, all execution commands apply only to the current thread |
| by default. That is, <code>continue</code> only continues one thread. |
| To continue all threads, issue <code>continue -a</code> or <code>c -a</code>. |
| </p> |
| <p>You can use <small>GDB</small>’s background execution commands |
| (see <a href="Background-Execution.html#Background-Execution">Background Execution</a>) to run some threads in the background |
| while you continue to examine or step others from <small>GDB</small>. |
| The MI execution commands (see <a href="GDB_002fMI-Program-Execution.html#GDB_002fMI-Program-Execution">GDB/MI Program Execution</a>) are |
| always executed asynchronously in non-stop mode. |
| </p> |
| <p>Suspending execution is done with the <code>interrupt</code> command when |
| running in the background, or <kbd>Ctrl-c</kbd> during foreground execution. |
| In all-stop mode, this stops the whole process; |
| but in non-stop mode the interrupt applies only to the current thread. |
| To stop the whole program, use <code>interrupt -a</code>. |
| </p> |
| <p>Other execution commands do not currently support the <code>-a</code> option. |
| </p> |
| <p>In non-stop mode, when a thread stops, <small>GDB</small> doesn’t automatically make |
| that thread current, as it does in all-stop mode. This is because the |
| thread stop notifications are asynchronous with respect to <small>GDB</small>’s |
| command interpreter, and it would be confusing if <small>GDB</small> unexpectedly |
| changed to a different thread just as you entered a command to operate on the |
| previously current thread. |
| </p> |
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| Next: <a href="Background-Execution.html#Background-Execution" accesskey="n" rel="next">Background Execution</a>, Previous: <a href="All_002dStop-Mode.html#All_002dStop-Mode" accesskey="p" rel="prev">All-Stop Mode</a>, Up: <a href="Thread-Stops.html#Thread-Stops" accesskey="u" rel="up">Thread Stops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
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