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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>11.2.4 Buffered Asynchronous Channels</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="icons.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" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x"><span style="font-weight: bold">The Racket Reference</span></a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language 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align="right">18 </td><td><a href="running.html" class="tocviewlink" data-pltdoc="x">Running Racket</a></td></tr><tr><td align="right"></td><td><a href="doc-bibliography.html" class="tocviewlink" data-pltdoc="x">Bibliography</a></td></tr><tr><td align="right"></td><td><a href="doc-index.html" class="tocviewlink" data-pltdoc="x">Index</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_1");">►</a></td><td>11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr></table><div class="tocviewsublist" style="display: none;" id="tocview_1"><table cellspacing="0" cellpadding="0"><tr><td align="right">11.1 </td><td><a href="threads.html" class="tocviewlink" data-pltdoc="x">Threads</a></td></tr><tr><td align="right">11.2 </td><td><a href="all-sync.html" class="tocviewselflink" data-pltdoc="x">Synchronization</a></td></tr><tr><td align="right">11.3 </td><td><a href="thread-local-storage.html" class="tocviewlink" data-pltdoc="x">Thread-<wbr></wbr>Local Storage</a></td></tr><tr><td align="right">11.4 </td><td><a href="futures.html" class="tocviewlink" data-pltdoc="x">Futures</a></td></tr><tr><td align="right">11.5 </td><td><a href="places.html" class="tocviewlink" data-pltdoc="x">Places</a></td></tr><tr><td align="right">11.6 </td><td><a href="engine.html" class="tocviewlink" data-pltdoc="x">Engines</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_2");">▼</a></td><td>11.2 </td><td><a href="all-sync.html" class="tocviewlink" data-pltdoc="x">Synchronization</a></td></tr></table><div class="tocviewsublist" style="display: block;" id="tocview_2"><table cellspacing="0" cellpadding="0"><tr><td align="right">11.2.1 </td><td><a href="sync.html" class="tocviewlink" data-pltdoc="x">Events</a></td></tr><tr><td align="right">11.2.2 </td><td><a href="channel.html" class="tocviewlink" data-pltdoc="x">Channels</a></td></tr><tr><td align="right">11.2.3 </td><td><a href="semaphore.html" class="tocviewlink" data-pltdoc="x">Semaphores</a></td></tr><tr><td align="right">11.2.4 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Buffered Asynchronous Channels</a></td></tr></table></div></div><div class="tocviewlist"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_3");">►</a></td><td>11.2.4 </td><td><a href="" class="tocviewselflink" data-pltdoc="x">Buffered Asynchronous Channels</a></td></tr></table><div class="tocviewsublistbottom" style="display: none;" id="tocview_3"><table cellspacing="0" cellpadding="0"><tr><td align="right">11.2.4.1 </td><td><a href="#%28part._.Creating_and_.Using_.Asynchronous_.Channels%29" class="tocviewlink" data-pltdoc="x">Creating and Using Asynchronous Channels</a></td></tr><tr><td align="right">11.2.4.2 </td><td><a href="#%28part._.Contracts_and_.Impersonators_on_.Asynchronous_.Channels%29" class="tocviewlink" data-pltdoc="x">Contracts and Impersonators on Asynchronous Channels</a></td></tr></table></div></div></div><div class="tocsub"><div class="tocsubtitle">On this page:</div><table class="tocsublist" cellspacing="0"><tr><td><span class="tocsublinknumber">11.2.4.1<tt> </tt></span><a href="#%28part._.Creating_and_.Using_.Asynchronous_.Channels%29" class="tocsubseclink" data-pltdoc="x">Creating and Using Asynchronous Channels</a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">async-<wbr></wbr>channel?</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._make-async-channel%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">make-<wbr></wbr>async-<wbr></wbr>channel</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">async-<wbr></wbr>channel-<wbr></wbr>get</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-try-get%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">async-<wbr></wbr>channel-<wbr></wbr>try-<wbr></wbr>get</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">async-<wbr></wbr>channel-<wbr></wbr>put</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put-evt%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">async-<wbr></wbr>channel-<wbr></wbr>put-<wbr></wbr>evt</span></span></a></td></tr><tr><td><span class="tocsublinknumber">11.2.4.2<tt> </tt></span><a href="#%28part._.Contracts_and_.Impersonators_on_.Asynchronous_.Channels%29" class="tocsubseclink" data-pltdoc="x">Contracts and Impersonators on Asynchronous Channels</a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel%2Fc%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">async-<wbr></wbr>channel/<span class="mywbr"> </span>c</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._impersonate-async-channel%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">impersonate-<wbr></wbr>async-<wbr></wbr>channel</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._chaperone-async-channel%29%29" class="tocsubnonseclink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">chaperone-<wbr></wbr>async-<wbr></wbr>channel</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, "6.7", "../");" 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("6.7");">top</a></span><span class="navright"> <a href="semaphore.html" title="backward to "11.2.3 Semaphores"" data-pltdoc="x">← prev</a> <a href="all-sync.html" title="up to "11.2 Synchronization"" data-pltdoc="x">up</a> <a href="thread-local-storage.html" title="forward to "11.3 Thread-Local Storage"" data-pltdoc="x">next →</a></span> </div><h5 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""async-channel"">11.2.4<tt> </tt><a name="(part._async-channel)"></a><a name="(mod-path._racket/async-channel)"></a>Buffered Asynchronous Channels</h5><p><div class="SIntrapara"><table cellspacing="0" cellpadding="0" class="defmodule"><tr><td align="left"><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="require.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._require%29%29" class="RktStxLink" data-pltdoc="x">require</a></span><span class="stt"> </span><a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/async-channel</span></a><span class="RktPn">)</span></td><td align="right"><span class="RpackageSpec"><span class="Smaller"> package:</span> <span class="stt">base</span></span></td></tr></table></div><div class="SIntrapara">The bindings documented in this section are provided by the <a href="" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/async-channel</span></a> library, not <a href="index.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket/base</span></a> or <a href="index.html" class="RktModLink" data-pltdoc="x"><span class="RktSym">racket</span></a>.</div></p><h5 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""Creating_and_Using_Asynchronous_Channels"">11.2.4.1<tt> </tt><a name="(part._.Creating_and_.Using_.Asynchronous_.Channels)"></a>Creating and Using Asynchronous Channels</h5><blockquote class="refpara"><blockquote class="refcolumn"><blockquote class="refcontent"><p><span class="imageleft"><img src="magnify.png" alt="+" width="24" height="24"/></span>See also <a href="threads.html#%28part._threadmbox%29" data-pltdoc="x">Thread Mailboxes</a>.</p></blockquote></blockquote></blockquote><p>An <a name="(tech._asynchronous._channel)"></a><span style="font-style: italic">asynchronous channel</span> is like a <a href="channel.html#%28tech._channel%29" class="techoutside" data-pltdoc="x"><span class="techinside">channel</span></a>, but it buffers
values so that a send operation does not wait on a receive operation.</p><p>In addition to its use with procedures that are specific to
asynchronous channels, an asynchronous channel can be used as a
<a href="sync.html#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable event</span></a> (see <a href="sync.html" data-pltdoc="x">Events</a>). An asynchronous
channel is <a href="sync.html#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a> when
<span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span> would not block; the asynchronous channel’s
<a href="sync.html#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> is the same as the
<span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span> result.</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._((lib._racket/async-channel..rkt)._async-channel~3f))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">async-channel?</a></span></span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._boolean~3f%29%29" class="RktValLink" data-pltdoc="x">boolean?</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">Returns <span class="RktVal">#t</span> if <span class="RktVar">v</span> is an asynchronous channel,
<span class="RktVal">#f</span> otherwise.</div></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._((lib._racket/async-channel..rkt)._make-async-channel))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._make-async-channel%29%29" class="RktValDef RktValLink" data-pltdoc="x">make-async-channel</a></span></span><span class="hspace"> </span>[<span class="RktVar">limit</span>]<span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">limit</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._exact-positive-integer~3f%29%29" class="RktValLink" data-pltdoc="x">exact-positive-integer?</a></span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="hspace"> </span>=<span class="hspace"> </span><span class="RktVal">#f</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns an asynchronous channel with a buffer limit of <span class="RktVar">limit</span>
items. A get operation blocks when the channel is empty, and a put
operation blocks when the channel has <span class="RktVar">limit</span> items already.
If <span class="RktVar">limit</span> is <span class="RktVal">#f</span>, the channel buffer has no limit (so
a put never blocks).</div></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._((lib._racket/async-channel..rkt)._async-channel-get))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValDef RktValLink" data-pltdoc="x">async-channel-get</a></span></span><span class="hspace"> </span><span class="RktVar">ach</span><span class="RktPn">)</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></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">ach</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Blocks until at least one value is available in <span class="RktVar">ach</span>, and then
returns the first of the values that were put into
<span class="RktSym">async-channel</span>.</div></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._((lib._racket/async-channel..rkt)._async-channel-try-get))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-try-get%29%29" class="RktValDef RktValLink" data-pltdoc="x">async-channel-try-get</a></span></span><span class="hspace"> </span><span class="RktVar">ach</span><span class="RktPn">)</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></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">ach</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">If at least one value is immediately available in <span class="RktVar">ach</span>,
returns the first of the values that were put into <span class="RktVar">ach</span>. If
<span class="RktSym">async-channel</span> is empty, the result is <span class="RktVal">#f</span>.</div></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._((lib._racket/async-channel..rkt)._async-channel-put))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValDef RktValLink" data-pltdoc="x">async-channel-put</a></span></span><span class="hspace"> </span><span class="RktVar">ach</span><span class="hspace"> </span><span class="RktVar">v</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><tr><td><span class="hspace"> </span><span class="RktVar">ach</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span></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">Puts <span class="RktVar">v</span> into <span class="RktVar">ach</span>, blocking if <span class="RktVar">ach</span>’s buffer
is full until space is available.</div></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._((lib._racket/async-channel..rkt)._async-channel-put-evt))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">async-channel-put-evt</a></span></span><span class="hspace"> </span><span class="RktVar">ach</span><span class="hspace"> </span><span class="RktVar">v</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="sync.html#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">ach</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span></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">Returns a <a href="sync.html#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable event</span></a> that is <a href="sync.html#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for
synchronization</span></a> when <span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span><span class="stt"> </span><span class="RktVar">ach</span><span class="stt"> </span><span class="RktVar">v</span><span class="RktPn">)</span> would return
a value (i.e., when the channel holds fewer values already than its
limit); the <a href="sync.html#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> of a asychronous channel-put event is the asychronous channel-put event itself.</div></p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">server</span><span class="hspace"> </span><span class="RktSym">input-channel</span><span class="hspace"> </span><span class="RktSym">output-channel</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="threads.html#%28def._%28%28quote._~23~25kernel%29._thread%29%29" class="RktValLink" data-pltdoc="x">thread</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">get</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span><span class="hspace"> </span><span class="RktSym">input-channel</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">put</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span><span class="hspace"> </span><span class="RktSym">output-channel</span><span class="hspace"> </span><span class="RktSym">x</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">do-large-computation</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._sqrt%29%29" class="RktValLink" data-pltdoc="x">sqrt</a></span><span class="hspace"> </span><span class="RktVal">9</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%29%29" class="RktStxLink" data-pltdoc="x">let</a></span><span class="hspace"> </span><span class="RktSym">loop</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym">data</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">get</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="case.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._case%29%29" class="RktStxLink" data-pltdoc="x">case</a></span><span class="hspace"> </span><span class="RktSym">data</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">quit</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</a></span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">add</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="begin.html#%28form._%28%28quote._~23~25kernel%29._begin%29%29" class="RktStxLink" data-pltdoc="x">begin</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">put</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._%2B%29%29" class="RktValLink" data-pltdoc="x">+</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">get</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">loop</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">get</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktPn">(</span><span class="RktSym">long</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="begin.html#%28form._%28%28quote._~23~25kernel%29._begin%29%29" class="RktStxLink" data-pltdoc="x">begin</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">put</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">do-large-computation</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">loop</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">get</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">to-server</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._make-async-channel%29%29" class="RktValLink" data-pltdoc="x">make-async-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">from-server</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._make-async-channel%29%29" class="RktValLink" data-pltdoc="x">make-async-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p> </p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym">server</span><span class="hspace"> </span><span class="RktSym">to-server</span><span class="hspace"> </span><span class="RktSym">from-server</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<thread></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span><span class="hspace"> </span><span class="RktSym">to-server</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._printf%29%29" class="RktValLink" data-pltdoc="x">printf</a></span><span class="hspace"> </span><span class="RktVal">"Adding 1 to 4\n"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">Adding 1 to 4</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span><span class="hspace"> </span><span class="RktSym">to-server</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">add</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span><span class="hspace"> </span><span class="RktSym">to-server</span><span class="hspace"> </span><span class="RktVal">4</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._printf%29%29" class="RktValLink" data-pltdoc="x">printf</a></span><span class="hspace"> </span><span class="RktVal">"Result is ~a\n"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span><span class="hspace"> </span><span class="RktSym">from-server</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">Result is 5</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._printf%29%29" class="RktValLink" data-pltdoc="x">printf</a></span><span class="hspace"> </span><span class="RktVal">"Ask server to do a long computation\n"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">Ask server to do a long computation</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span><span class="hspace"> </span><span class="RktSym">to-server</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">long</span><span class="RktPn">)</span></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._printf%29%29" class="RktValLink" data-pltdoc="x">printf</a></span><span class="hspace"> </span><span class="RktVal">"I can do other stuff\n"</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">I can do other stuff</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._printf%29%29" class="RktValLink" data-pltdoc="x">printf</a></span><span class="hspace"> </span><span class="RktVal">"Ok, computation from server is ~a\n"</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span><span class="hspace"> </span><span class="RktSym">from-server</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">Ok, computation from server is 3</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span><span class="hspace"> </span><span class="RktSym">to-server</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">quit</span><span class="RktPn">)</span></td></tr></table></blockquote></div></p><h5 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-source-pkg="racket-doc" x-part-tag=""Contracts_and_Impersonators_on_Asynchronous_Channels"">11.2.4.2<tt> </tt><a name="(part._.Contracts_and_.Impersonators_on_.Asynchronous_.Channels)"></a>Contracts and Impersonators on Asynchronous Channels</h5><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._((lib._racket/async-channel..rkt)._async-channel/c))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">async-channel/c</a></span></span><span class="hspace"> </span><span class="RktVar">c</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">c</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a contract that recognizes asynchronous channels. Values put into or
retrieved from the channel must match <span class="RktVar">c</span>.</div></p><p>If the <span class="RktVar">c</span> argument is a flat contract or a chaperone contract, then the
result will be a chaperone contract. Otherwise, the result will be an
impersonator contract.</p><p>When an <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel%2Fc%29%29" class="RktValLink" data-pltdoc="x">async-channel/c</a></span> contract is applied to an asynchronous channel,
the result is not <span class="RktSym"><a href="booleans.html#%28def._%28%28quote._~23~25kernel%29._eq~3f%29%29" class="RktValLink" data-pltdoc="x">eq?</a></span> to the input. The result will be either a
<a href="chaperones.html#%28tech._chaperone%29" class="techoutside" data-pltdoc="x"><span class="techinside">chaperone</span></a> or <a href="chaperones.html#%28tech._impersonator%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator</span></a> of the input depending on the type of
contract.</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><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/async-channel..rkt)._impersonate-async-channel))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._impersonate-async-channel%29%29" class="RktValDef RktValLink" data-pltdoc="x">impersonate-async-channel</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">channel</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">get-proc</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">put-proc</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">prop</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">prop-val</span><span class="hspace"> </span><span class="RktMeta">...</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktMeta">...</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span><span class="hspace"> </span><span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._impersonator~3f%29%29" class="RktValLink" data-pltdoc="x">impersonator?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">channel</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">get-proc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</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><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</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><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">put-proc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</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><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</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><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">prop</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._impersonator-property~3f%29%29" class="RktValLink" data-pltdoc="x">impersonator-property?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">prop-val</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></td></tr></table></blockquote></div><div class="SIntrapara">Returns an impersonator of <span class="RktVar">channel</span>, which redirects the
<span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span> and <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span> operations.</div></p><p>The <span class="RktVar">get-proc</span> must accept the value that <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span>
produces on <span class="RktVar">channel</span>; it must produce a replacement value, which is the
result of the get operation on the impersonator.</p><p>The <span class="RktVar">put-proc</span> must accept the value passed to <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span>
called on <span class="RktVar">channel</span>; it must produce a replacement value, which is the
value passed to the put procedure called on the original channel.</p><p>The <span class="RktVar">get-proc</span> and <span class="RktVar">put-proc</span> procedures are called for all
operations that get or put values from the channel, not just
<span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-get%29%29" class="RktValLink" data-pltdoc="x">async-channel-get</a></span> and <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel-put%29%29" class="RktValLink" data-pltdoc="x">async-channel-put</a></span>.</p><p>Pairs of <span class="RktVar">prop</span> and <span class="RktVar">prop-val</span> (the number of arguments to
<span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._impersonate-async-channel%29%29" class="RktValLink" data-pltdoc="x">impersonate-async-channel</a></span> must be odd) add
<a href="chaperones.html#%28tech._impersonator._property%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator properties</span></a> or override <a href="chaperones.html#%28tech._impersonator._property%29" class="techoutside" data-pltdoc="x"><span class="techinside">impersonator property</span></a> values
of <span class="RktVar">channel</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><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/async-channel..rkt)._chaperone-async-channel))"></a><span title="Provided from: racket/async-channel | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._chaperone-async-channel%29%29" class="RktValDef RktValLink" data-pltdoc="x">chaperone-async-channel</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">channel</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">get-proc</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">put-proc</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">prop</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">prop-val</span><span class="hspace"> </span><span class="RktMeta">...</span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktMeta">...</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span><span class="hspace"> </span><span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._chaperone~3f%29%29" class="RktValLink" data-pltdoc="x">chaperone?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">channel</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._async-channel~3f%29%29" class="RktValLink" data-pltdoc="x">async-channel?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">get-proc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</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><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</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><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">put-proc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</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><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</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><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">prop</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._impersonator-property~3f%29%29" class="RktValLink" data-pltdoc="x">impersonator-property?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">prop-val</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></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fasync-channel..rkt%29._impersonate-async-channel%29%29" class="RktValLink" data-pltdoc="x">impersonate-async-channel</a></span>, but the <span class="RktVar">get-proc</span> procedure
must produce the same value or a chaperone of the original value, and
<span class="RktVar">put-proc</span> must produce the same value or a chaperone of the original
value.</div></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, "6.7", "../");" 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("6.7");">top</a></span><span class="navright"> <a href="semaphore.html" title="backward to "11.2.3 Semaphores"" data-pltdoc="x">← prev</a> <a href="all-sync.html" title="up to "11.2 Synchronization"" data-pltdoc="x">up</a> <a href="thread-local-storage.html" title="forward to "11.3 Thread-Local Storage"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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