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108 lines
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HTML
108 lines
5.0 KiB
HTML
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<title>Invoking the garbage collector (GNU Compiler Collection (GCC) Internals)</title>
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Type-Information.html#Type-Information" rel="up" title="Type Information">
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<link href="Troubleshooting.html#Troubleshooting" rel="next" title="Troubleshooting">
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<a name="Invoking-the-garbage-collector"></a>
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<p>
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Next: <a href="Troubleshooting.html#Troubleshooting" accesskey="n" rel="next">Troubleshooting</a>, Previous: <a href="Files.html#Files" accesskey="p" rel="prev">Files</a>, Up: <a href="Type-Information.html#Type-Information" accesskey="u" rel="up">Type Information</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="How-to-invoke-the-garbage-collector"></a>
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<h3 class="section">23.6 How to invoke the garbage collector</h3>
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<a name="index-garbage-collector_002c-invocation"></a>
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<a name="index-ggc_005fcollect"></a>
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<p>The GCC garbage collector GGC is only invoked explicitly. In contrast
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with many other garbage collectors, it is not implicitly invoked by
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allocation routines when a lot of memory has been consumed. So the
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only way to have GGC reclaim storage is to call the <code>ggc_collect</code>
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function explicitly. This call is an expensive operation, as it may
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have to scan the entire heap. Beware that local variables (on the GCC
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call stack) are not followed by such an invocation (as many other
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garbage collectors do): you should reference all your data from static
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or external <code>GTY</code>-ed variables, and it is advised to call
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<code>ggc_collect</code> with a shallow call stack. The GGC is an exact mark
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and sweep garbage collector (so it does not scan the call stack for
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pointers). In practice GCC passes don’t often call <code>ggc_collect</code>
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themselves, because it is called by the pass manager between passes.
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</p>
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<p>At the time of the <code>ggc_collect</code> call all pointers in the GC-marked
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structures must be valid or <code>NULL</code>. In practice this means that
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there should not be uninitialized pointer fields in the structures even
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if your code never reads or writes those fields at a particular
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instance. One way to ensure this is to use cleared versions of
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allocators unless all the fields are initialized manually immediately
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after allocation.
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</p>
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