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<title>GNU Compiler Collection (GCC) Internals: Plugins GC</title>

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<a name="Interacting-with-the-GCC-Garbage-Collector"></a>
<h3 class="section">23.4 Interacting with the GCC Garbage Collector</h3>

<p>Some plugins may want to be informed when GGC (the GCC Garbage
Collector) is running. They can register callbacks for the
<code>PLUGIN_GGC_START</code> and <code>PLUGIN_GGC_END</code> events (for which
the callback is called with a null <code>gcc_data</code>) to be notified of
the start or end of the GCC garbage collection.
</p>
<p>Some plugins may need to have GGC mark additional data. This can be
done by registering a callback (called with a null <code>gcc_data</code>)
for the <code>PLUGIN_GGC_MARKING</code> event. Such callbacks can call the
<code>ggc_set_mark</code> routine, preferably through the <code>ggc_mark</code> macro
(and conversely, these routines should usually not be used in plugins
outside of the <code>PLUGIN_GGC_MARKING</code> event).
</p>
<p>Some plugins may need to add extra GGC root tables, e.g. to handle their own
<code>GTY</code>-ed data. This can be done with the <code>PLUGIN_REGISTER_GGC_ROOTS</code>
pseudo-event with a null callback and the extra root table (of type <code>struct
ggc_root_tab*</code>) as <code>user_data</code>.  Plugins that want to use the
<code>if_marked</code> hash table option can add the extra GGC cache tables generated
by <code>gengtype</code> using the <code>PLUGIN_REGISTER_GGC_CACHES</code> pseudo-event with
a null callback and the extra cache table (of type <code>struct ggc_cache_tab*</code>)
as <code>user_data</code>.  Running the <code>gengtype -p <var>source-dir</var>
<var>file-list</var> <var>plugin*.c</var> ...</code> utility generates these extra root tables.
</p>
<p>You should understand the details of memory management inside GCC
before using <code>PLUGIN_GGC_MARKING</code>, <code>PLUGIN_REGISTER_GGC_ROOTS</code>
or <code>PLUGIN_REGISTER_GGC_CACHES</code>.
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