109 lines
5.1 KiB
HTML
109 lines
5.1 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>GNU Compiler Collection (GCC) Internals: Invoking the garbage collector</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals: Invoking the garbage collector">
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<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Invoking the garbage collector">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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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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<link href="Files.html#Files" rel="prev" title="Files">
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Invoking-the-garbage-collector"></a>
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<div class="header">
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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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</div>
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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">22.6 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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</body>
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</html>
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