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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>16.4 Garbage Collection</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" 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class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewselflink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="running.html" 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data-pltdoc="x">Ephemerons</a></td></tr><tr><td align="right">16.3 </td><td><a href="willexecutor.html" class="tocviewlink" data-pltdoc="x">Wills and Executors</a></td></tr><tr><td align="right">16.4 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Garbage Collection</a></td></tr><tr><td align="right">16.5 </td><td><a href="phantom-bytes.html" class="tocviewlink" data-pltdoc="x">Phantom Byte Strings</a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._collect-garbage%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">collect-<wbr></wbr>garbage</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._current-memory-use%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">current-<wbr></wbr>memory-<wbr></wbr>use</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._dump-memory-stats%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">dump-<wbr></wbr>memory-<wbr></wbr>stats</span></span></a></td></tr></table></div></div><div class="maincolumn"><div class="main"><div class="navsettop"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "6.1", "../");" onfocus="this.style.color="black"; this.style.textAlign="left"; if (this.value == "...search manuals...") this.value="";" onblur="if (this.value.match(/^ *$/)) { this.style.color="#888"; this.style.textAlign="center"; this.value="...search manuals..."; }"/></form> <a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("6.1");">top</a></span><span class="navright"> <a href="willexecutor.html" title="backward to "16.3 Wills and Executors"" data-pltdoc="x">← prev</a> <a href="memory.html" title="up to "16 Memory Management"" data-pltdoc="x">up</a> <a href="phantom-bytes.html" title="forward to "16.5 Phantom Byte Strings"" data-pltdoc="x">next →</a></span> </div><h4 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-part-tag=""garbagecollection"">16.4<tt> </tt><a name="(part._garbagecollection)"></a>Garbage Collection</h4><p>Set the <a name="(idx._(gentag._363._(lib._scribblings/reference/reference..scrbl)))"></a><span class="stt">PLTDISABLEGC</span> environment variable (to any
value) before Racket starts to disable <a href="eval-model.html#%28tech._garbage._collection%29" class="techoutside" data-pltdoc="x"><span class="techinside">garbage collection</span></a>.</p><p>In Racket 3m (the main variant of Racket), each garbage collection
logs a message (see <a href="logging.html" data-pltdoc="x">Logging</a>) at the <span class="RktVal">'</span><span class="RktVal">debug</span> level to a logger named <span class="RktVal">'</span><span class="RktVal">GC</span>.
The data portion of the message is an instance of a <a name="(idx._(gentag._364._(lib._scribblings/reference/reference..scrbl)))"></a><span class="RktSym">gc-info</span>
<a href="structures.html#%28tech._prefab%29" class="techoutside" data-pltdoc="x"><span class="techinside">prefab</span></a> structure type with 10 fields as follows, but future
versions of Racket may use a <span class="RktSym">gc-info</span> <a href="structures.html#%28tech._prefab%29" class="techoutside" data-pltdoc="x"><span class="techinside">prefab</span></a> structure
with additional fields:</p><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span><span class="hspace"> </span><span class="RktSym">gc-info</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">major?</span><span class="hspace"> </span><span class="RktSym">pre-amount</span><span class="hspace"> </span><span class="RktSym">pre-admin-amount</span><span class="hspace"> </span><span class="RktSym">code-amount</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">post-amount</span><span class="hspace"> </span><span class="RktSym">post-admin-amount</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">start-process-time</span><span class="hspace"> </span><span class="RktSym">end-process-time</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">start-time</span><span class="hspace"> </span><span class="RktSym">end-time</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">#:prefab</span><span class="RktPn">)</span></td></tr></table></blockquote><p>The <span class="RktSym">major?</span> field indicates whether the collection was a
“major” collection that inspects all memory or a “minor”
collection that mostly inspects just recent allocations. The
<span class="RktSym">pre-amount</span> field reports place-local memory use (i.e., not
counting the memory use of child places) in bytes at the time that the
<a href="eval-model.html#%28tech._garbage._collection%29" class="techoutside" data-pltdoc="x"><span class="techinside">garbage collection</span></a> started. The <span class="RktSym">pre-admin-amount</span> is a
larger number that includes memory use for the garbage collector’s
overhead (such as space on memory pages that is not yet used). The
<span class="RktSym">code-amount</span> field reports additional memory use for generated
native code (which is the same just before and after a garbage
collection, since it is released via finalization). The
<span class="RktSym">post-amount</span> and <span class="RktSym">post-admin-amount</span> fields correspond
to <span class="RktSym">pre-amount</span> and <span class="RktSym">pre-admin-amount</span>, but after garbage
collection. The <span class="RktSym">start-process-time</span> and
<span class="RktSym">end-process-time</span> fields report processor time (in the sense
of <span class="RktSym"><a href="time.html#%28def._%28%28quote._~23~25kernel%29._current-process-milliseconds%29%29" class="RktValLink" data-pltdoc="x">current-process-milliseconds</a></span>) at the start and end of
garbage collection; the difference is the processor time consumed by
collection. The <span class="RktSym">start-time</span> and <span class="RktSym">end-time</span> fields
report real time (in the sense of
<span class="RktSym"><a href="time.html#%28def._%28%28quote._~23~25kernel%29._current-inexact-milliseconds%29%29" class="RktValLink" data-pltdoc="x">current-inexact-milliseconds</a></span>) at the start and end of garbage
collection; the difference is the real time consumed by garbage
collection.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._collect-garbage))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._collect-garbage%29%29" class="RktValDef RktValLink" data-pltdoc="x">collect-garbage</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void~3f%29%29" class="RktValLink" data-pltdoc="x">void?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Forces an immediate <a href="eval-model.html#%28tech._garbage._collection%29" class="techoutside" data-pltdoc="x"><span class="techinside">garbage collection</span></a> (unless garbage
collection is disabled by setting <span class="stt">PLTDISABLEGC</span>). Some
effectively unreachable data may remain uncollected, because the
collector cannot prove that it is unreachable.</div></p><p>The <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._collect-garbage%29%29" class="RktValLink" data-pltdoc="x">collect-garbage</a></span> procedure provides some control over the
timing of collections, but garbage will obviously be collected even if
this procedure is never called (unless garbage collection is disabled).</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._current-memory-use))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._current-memory-use%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-memory-use</a></span></span><span class="hspace"> </span>[<span class="RktVar">cust</span>]<span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-nonnegative-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-nonnegative-integer?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">cust</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="custodians.html#%28def._%28%28quote._~23~25kernel%29._custodian~3f%29%29" class="RktValLink" data-pltdoc="x">custodian?</a></span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns an estimate of the number of bytes of memory occupied by
reachable data from <span class="RktVar">cust</span>. This estimate is calculated by the
last garbage collection, and can be 0 if none occurred (or if none occurred
since the given custodian was created). The <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._current-memory-use%29%29" class="RktValLink" data-pltdoc="x">current-memory-use</a></span>
function does <span style="font-style: italic">not</span> perform a collection by itself; doing one
before the call will generally decrease the result (or increase it from
0 if no collections happened yet).</div></p><p>If <span class="RktVar">cust</span> is not provided, the estimate is a total reachable from
any custodians.</p><p>When Racket is compiled without support for memory accounting, the
estimate is the same (i.e., all memory) for any individual custodian;
see also <span class="RktSym"><a href="custodians.html#%28def._%28%28quote._~23~25kernel%29._custodian-memory-accounting-available~3f%29%29" class="RktValLink" data-pltdoc="x">custodian-memory-accounting-available?</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._dump-memory-stats))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._dump-memory-stats%29%29" class="RktValDef RktValLink" data-pltdoc="x">dump-memory-stats</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Dumps information about memory usage to the low-level error port
or console.</div></p><p>Various combinations of <span class="RktVar">v</span> arguments can control the
information in a dump. The information that is available depends on
your Racket build; check the end of a dump from a particular build to
see if it offers additional information; otherwise, all <span class="RktVar">v</span>s are
ignored.</p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" style="color: #888;" type="text" value="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "6.1", "../");" onfocus="this.style.color="black"; this.style.textAlign="left"; if (this.value == "...search manuals...") this.value="";" onblur="if (this.value.match(/^ *$/)) { this.style.color="#888"; this.style.textAlign="center"; this.value="...search manuals..."; }"/></form> <a href="../index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("6.1");">top</a></span><span class="navright"> <a href="willexecutor.html" title="backward to "16.3 Wills and Executors"" data-pltdoc="x">← prev</a> <a href="memory.html" title="up to "16 Memory Management"" data-pltdoc="x">up</a> <a href="phantom-bytes.html" title="forward to "16.5 Phantom Byte Strings"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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