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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><title>11.2.1 Events</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" 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 Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewlink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewselflink" 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="tocviewlink" 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" 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="tocviewsublistbottom" style="display: block;" id="tocview_2"><table cellspacing="0" cellpadding="0"><tr><td align="right">11.2.1 </td><td><a href="" class="tocviewselflink" 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="async-channel.html" class="tocviewlink" data-pltdoc="x">Buffered 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><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">evt?</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sync</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sync/<span class="mywbr"> </span>timeout</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Fenable-break%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sync/<span class="mywbr"> </span>enable-<wbr></wbr>break</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%2Fenable-break%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">sync/<span class="mywbr"> </span>timeout/<span class="mywbr"> </span>enable-<wbr></wbr>break</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">choice-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._wrap-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">wrap-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">handle-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._guard-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">guard-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._nack-guard-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">nack-<wbr></wbr>guard-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._poll-guard-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">poll-<wbr></wbr>guard-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._always-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">always-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._never-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">never-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._system-idle-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">system-<wbr></wbr>idle-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._alarm-evt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">alarm-<wbr></wbr>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt~3f%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">handle-<wbr></wbr>evt?</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._prop~3aevt%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">prop:<span class="mywbr"> </span>evt</span></span></a></td></tr><tr><td><a href="#%28def._%28%28quote._~23~25kernel%29._current-evt-pseudo-random-generator%29%29" class="tocsublink" data-pltdoc="x"><span class="RktSym"><span class="RktValLink">current-<wbr></wbr>evt-<wbr></wbr>pseudo-<wbr></wbr>random-<wbr></wbr>generator</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="all-sync.html" title="backward to "11.2 Synchronization"" data-pltdoc="x">← prev</a> <a href="all-sync.html" title="up to "11.2 Synchronization"" data-pltdoc="x">up</a> <a href="channel.html" title="forward to "11.2.2 Channels"" data-pltdoc="x">next →</a></span> </div><h5 x-source-module="(lib "scribblings/reference/reference.scrbl")" x-part-tag=""sync"">11.2.1<tt> </tt><a name="(part._sync)"></a><a name="(idx._(gentag._178._(lib._scribblings/reference/reference..scrbl)))"></a><a name="(idx._(gentag._179._(lib._scribblings/reference/reference..scrbl)))"></a>Events</h5><p>A <a name="(tech._synchronizable._event)"></a><span style="font-style: italic">synchronizable event</span> (or just <span style="font-style: italic">event</span> for short)
works with the <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span> procedure to coordinate synchronization
among threads. Certain kinds of objects double as events, including
ports and threads. Other kinds of objects exist only for their use as
events.</p><p>At any point in time, an event is either <a name="(tech._ready._for._synchronization)"></a><span style="font-style: italic">ready for
synchronization</span>, or it is not; depending on the kind of event and how
it is used by other threads, an event can switch from not ready to
ready (or back), at any time. If a thread synchronizes on an event
when it is ready, then the event produces a particular
<a name="(tech._synchronization._result)"></a><span style="font-style: italic">synchronization result</span>.</p><p>Synchronizing an event may affect the state of the event. For example,
when synchronizing a semaphore, then the semaphore’s internal count is
decremented, just as with <span class="RktSym"><a href="semaphore.html#%28def._%28%28quote._~23~25kernel%29._semaphore-wait%29%29" class="RktValLink" data-pltdoc="x">semaphore-wait</a></span>. For most kinds of
events, however (such as a port), synchronizing does not modify the
event’s state.</p><p>Racket values that act as <a href="#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable events</span></a> include
<a href="semaphore.html#%28tech._semaphore%29" class="techoutside" data-pltdoc="x"><span class="techinside">semaphores</span></a>, <a href="channel.html#%28tech._channel%29" class="techoutside" data-pltdoc="x"><span class="techinside">channels</span></a>, <a href="async-channel.html#%28tech._asynchronous._channel%29" class="techoutside" data-pltdoc="x"><span class="techinside">asynchronous channels</span></a>,
<a href="ports.html#%28tech._port%29" class="techoutside" data-pltdoc="x"><span class="techinside">ports</span></a>, <a href="tcp.html#%28tech._tcp._listener%29" class="techoutside" data-pltdoc="x"><span class="techinside">TCP listeners</span></a>, <a href="logging.html#%28tech._log._receiver%29" class="techoutside" data-pltdoc="x"><span class="techinside">log receiver</span></a>s, <a href="eval-model.html#%28tech._thread%29" class="techoutside" data-pltdoc="x"><span class="techinside">threads</span></a>,
<a href="subprocess.html#%28tech._subproces%29" class="techoutside" data-pltdoc="x"><span class="techinside">subprocess</span></a>es, <a href="willexecutor.html#%28tech._will._executor%29" class="techoutside" data-pltdoc="x"><span class="techinside">will executors</span></a>, and <a href="eval-model.html#%28tech._custodian._box%29" class="techoutside" data-pltdoc="x"><span class="techinside">custodian
box</span></a>es. Libraries can define new synchronizable events, especially
though <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._prop~3aevt%29%29" class="RktValLink" data-pltdoc="x">prop:evt</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)._evt~3f))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">evt?</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 a <a href="#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable event</span></a>,
<span class="RktVal">#f</span> otherwise.</div></p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._never-evt%29%29" class="RktValLink" data-pltdoc="x">never-evt</a></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="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</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="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr></table></blockquote></td></tr></table></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)._sync))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValDef RktValLink" data-pltdoc="x">sync</a></span></span><span class="hspace"> </span><span class="RktVar">evt</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">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Blocks as long as none of the <a href="#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable events</span></a>
<span class="RktVar">evt</span>s are ready, as defined above.</div></p><p>When at least one <span class="RktVar">evt</span> is ready, its <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization
result</span></a> (often <span class="RktVar">evt</span> itself) is returned. If multiple
<span class="RktVar">evt</span>s are ready, one of the <span class="RktVar">evt</span>s is chosen
pseudo-randomly for the result; the
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._current-evt-pseudo-random-generator%29%29" class="RktValLink" data-pltdoc="x">current-evt-pseudo-random-generator</a></span> parameter sets the
random-number generator that controls this choice.</p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </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="RktSym">ch</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._displayln%29%29" class="RktValLink" data-pltdoc="x">displayln</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktSym">ch</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</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="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-put%29%29" class="RktValLink" data-pltdoc="x">channel-put</a></span><span class="hspace"> </span><span class="RktSym">ch</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">hellooooo</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">hellooooo</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></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)._sync/timeout))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValDef RktValLink" data-pltdoc="x">sync/timeout</a></span></span><span class="hspace"> </span><span class="RktVar">timeout</span><span class="hspace"> </span><span class="RktVar">evt</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">timeout</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="RktVal">#f</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._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></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._not%2Fc%29%29" class="RktValLink" data-pltdoc="x">not/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._negative~3f%29%29" class="RktValLink" data-pltdoc="x">negative?</a></span><span class="RktPn">)</span><span class="RktPn">)</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="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><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span> if <span class="RktVar">timeout</span> is <span class="RktVal">#f</span>. If
<span class="RktVar">timeout</span> is a real number, then the result is <span class="RktVal">#f</span>
if <span class="RktVar">timeout</span> seconds pass without a
successful synchronization. If <span class="RktVar">timeout</span> is a procedure, then
it is called in tail position if polling the <span class="RktVar">evt</span>s discovers
no ready events.</div></p><p>A zero value for <span class="RktVar">timeout</span> is equivalent to <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="stt"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="stt"> </span><span class="RktVal">#f</span><span class="RktPn">)</span>. In either case, each <span class="RktVar">evt</span> is checked at least once
before returning <span class="RktVal">#f</span> or calling <span class="RktVar">timeout</span>.</p><p>See also <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._alarm-evt%29%29" class="RktValLink" data-pltdoc="x">alarm-evt</a></span> for an alternative timeout mechanism.</p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktCmt">;</span><span class="RktCmt"> </span><span class="RktCmt">times out before waking up</span></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="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">0.5</span></td></tr><tr><td><span class="hspace"> </span><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._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="threads.html#%28def._%28%28quote._~23~25kernel%29._sleep%29%29" class="RktValLink" data-pltdoc="x">sleep</a></span><span class="hspace"> </span><span class="RktVal">1</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._displayln%29%29" class="RktValLink" data-pltdoc="x">displayln</a></span><span class="hspace"> </span><span class="RktVal">"woke up!"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktRes">#f</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="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._displayln%29%29" class="RktValLink" data-pltdoc="x">displayln</a></span><span class="hspace"> </span><span class="RktVal">"no ready events"</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._never-evt%29%29" class="RktValLink" data-pltdoc="x">never-evt</a></span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">no ready events</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></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)._sync/enable-break))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Fenable-break%29%29" class="RktValDef RktValLink" data-pltdoc="x">sync/enable-break</a></span></span><span class="hspace"> </span><span class="RktVar">evt</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">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span>, but breaking is enabled (see
<a href="breakhandler.html" data-pltdoc="x">Breaks</a>) while waiting on the <span class="RktVar">evt</span>s. If
breaking is disabled when <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Fenable-break%29%29" class="RktValLink" data-pltdoc="x">sync/enable-break</a></span> is called, then
either all <span class="RktVar">evt</span>s remain unchosen or the <span class="RktSym"><a href="exns.html#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._exn~3abreak%29%29" class="RktValLink" data-pltdoc="x">exn:break</a></span>
exception is raised, but not both.</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._((quote._~23~25kernel)._sync/timeout/enable-break))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%2Fenable-break%29%29" class="RktValDef RktValLink" data-pltdoc="x">sync/timeout/enable-break</a></span></span><span class="hspace"> </span><span class="RktVar">timeout</span><span class="hspace"> </span><span class="RktVar">evt</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">timeout</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="RktVal">#f</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._and%2Fc%29%29" class="RktValLink" data-pltdoc="x">and/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></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._not%2Fc%29%29" class="RktValLink" data-pltdoc="x">not/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._negative~3f%29%29" class="RktValLink" data-pltdoc="x">negative?</a></span><span class="RktPn">)</span><span class="RktPn">)</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="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><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Fenable-break%29%29" class="RktValLink" data-pltdoc="x">sync/enable-break</a></span>, but with a timeout as for <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></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._((quote._~23~25kernel)._choice-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">choice-evt</a></span></span><span class="hspace"> </span><span class="RktVar">evt</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="#%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">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Creates and returns a single event that combines the
<span class="RktVar">evt</span>s. Supplying the result to <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span> is the same as
supplying each <span class="RktVar">evt</span> to the same call.</div></p><p>That is, an event returned by <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29" class="RktValLink" data-pltdoc="x">choice-evt</a></span> is <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for
synchronization</span></a> when one or more of the <span class="RktVar">evt</span>s supplied to
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29" class="RktValLink" data-pltdoc="x">choice-evt</a></span> are <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a>. If the
choice event is chosen, one of its ready <span class="RktVar">evt</span>s is chosen
pseudo-randomly, and the <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> is the chosen
<span class="RktVar">evt</span>’s <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a>.</p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </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="RktSym">ch1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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="RktSym">ch2</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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="RktSym">either-channel</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29" class="RktValLink" data-pltdoc="x">choice-evt</a></span><span class="hspace"> </span><span class="RktSym">ch1</span><span class="hspace"> </span><span class="RktSym">ch2</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._displayln%29%29" class="RktValLink" data-pltdoc="x">displayln</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktSym">either-channel</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<thread></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="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-put%29%29" class="RktValLink" data-pltdoc="x">channel-put</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="if.html#%28form._%28%28quote._~23~25kernel%29._if%29%29" class="RktStxLink" data-pltdoc="x">if</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._~3e%29%29" class="RktValLink" data-pltdoc="x">></a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._random%29%29" class="RktValLink" data-pltdoc="x">random</a></span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">0.5</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">ch1</span><span class="hspace"> </span><span class="RktSym">ch2</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">tuturuu</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">tuturuu</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></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)._wrap-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._wrap-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">wrap-evt</a></span></span><span class="hspace"> </span><span class="RktVar">evt</span><span class="hspace"> </span><span class="RktVar">wrap</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%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">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">wrap</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="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</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#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Creates an event that is <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a> when
<span class="RktVar">evt</span> is <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a>, but whose
<a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> is determined by applying <span class="RktVar">wrap</span>
to the <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> of <span class="RktVar">evt</span>. The number
of arguments accetped by <span class="RktVar">wrap</span> must match the number of values
for the synchronization result of <span class="RktVar">evt</span>.</div></p><p>The call to <span class="RktVar">wrap</span> is
<span class="RktSym"><a href="breakhandler.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._parameterize-break%29%29" class="RktStxLink" data-pltdoc="x">parameterize-break</a></span>ed to disable breaks initially.</p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </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="RktSym">ch</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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="RktVar">evt</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._wrap-evt%29%29" class="RktValLink" data-pltdoc="x">wrap-evt</a></span><span class="hspace"> </span><span class="RktSym">ch</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">v</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._format%29%29" class="RktValLink" data-pltdoc="x">format</a></span><span class="hspace"> </span><span class="RktVal">"you've got mail: ~a"</span><span class="hspace"> </span><span class="RktSym">v</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._displayln%29%29" class="RktValLink" data-pltdoc="x">displayln</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktVar">evt</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</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="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-put%29%29" class="RktValLink" data-pltdoc="x">channel-put</a></span><span class="hspace"> </span><span class="RktSym">ch</span><span class="hspace"> </span><span class="RktVal">"Dear Alice ..."</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">you've got mail: Dear Alice ...</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></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)._handle-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">handle-evt</a></span></span><span class="hspace"> </span><span class="RktVar">evt</span><span class="hspace"> </span><span class="RktVar">handle</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt~3f%29%29" class="RktValLink" data-pltdoc="x">handle-evt?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">handle</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="RktSym"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</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#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._wrap-evt%29%29" class="RktValLink" data-pltdoc="x">wrap-evt</a></span>, except that <span class="RktVar">handle</span> is called in <a href="eval-model.html#%28tech._tail._position%29" class="techoutside" data-pltdoc="x"><span class="techinside">tail
position</span></a> with respect to the synchronization request—<wbr></wbr>and without
breaks explicitly disabled—<wbr></wbr>when it is not wrapped by <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._wrap-evt%29%29" class="RktValLink" data-pltdoc="x">wrap-evt</a></span>,
<span class="RktSym"><a href="chaperones.html#%28def._%28%28quote._~23~25kernel%29._chaperone-evt%29%29" class="RktValLink" data-pltdoc="x">chaperone-evt</a></span>, or another <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt%29%29" class="RktValLink" data-pltdoc="x">handle-evt</a></span>.</div></p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </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="RktSym">msg-ch</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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="RktSym">exit-ch</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28quote._~23~25kernel%29._make-channel%29%29" class="RktValLink" data-pltdoc="x">make-channel</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></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="threads.html#%28def._%28%28quote._~23~25kernel%29._thread%29%29" class="RktValLink" data-pltdoc="x">thread</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><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">val</span><span class="hspace"> </span><span class="RktVal">0</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </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">"val = ~a~n"</span><span class="hspace"> </span><span class="RktSym">val</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt%29%29" class="RktValLink" data-pltdoc="x">handle-evt</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym">msg-ch</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">loop</span><span class="hspace"> </span><span class="RktSym">val</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt%29%29" class="RktValLink" data-pltdoc="x">handle-evt</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym">exit-ch</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">val</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._displayln%29%29" class="RktValLink" data-pltdoc="x">displayln</a></span><span class="hspace"> </span><span class="RktSym">val</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></table></td></tr><tr><td><p><span class="RktOut">val = 0</span></p></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="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-put%29%29" class="RktValLink" data-pltdoc="x">channel-put</a></span><span class="hspace"> </span><span class="RktSym">msg-ch</span><span class="hspace"> </span><span class="RktVal">5</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">val = 5</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-put%29%29" class="RktValLink" data-pltdoc="x">channel-put</a></span><span class="hspace"> </span><span class="RktSym">msg-ch</span><span class="hspace"> </span><span class="RktVal">7</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">val = 7</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="channel.html#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._channel-put%29%29" class="RktValLink" data-pltdoc="x">channel-put</a></span><span class="hspace"> </span><span class="RktSym">exit-ch</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">done</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktOut">done</span></p></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></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/private/misc..rkt)._guard-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._guard-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">guard-evt</a></span></span><span class="hspace"> </span><span class="RktVar">maker</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%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">maker</span><span class="hspace"> </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="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Creates a value that behaves as an event, but that is actually an
event maker.</div></p><p>An event <span class="RktVar">guard</span> returned by <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._guard-evt%29%29" class="RktValLink" data-pltdoc="x">guard-evt</a></span> generates an
event when <span class="RktVar">guard</span> is used with <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span>
(or whenever it is part of a choice event used with <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span>,
etc.), where the generated event is the result of calling
<span class="RktVar">maker</span>. The <span class="RktVar">maker</span> procedure may be called by
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span> at most once for a given call to <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span>, but
<span class="RktVar">maker</span> may not be called if a ready event is chosen before
<span class="RktVar">guard</span> is even considered.</p><p>If <span class="RktVar">maker</span> returns a non-event, then <span class="RktVar">maker</span>’s
result is replaced with an event that is <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for
synchronization</span></a> and whose <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> is
<span class="RktVar">guard</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)._nack-guard-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._nack-guard-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">nack-guard-evt</a></span></span><span class="hspace"> </span><span class="RktVar">maker</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%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">maker</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</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="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._guard-evt%29%29" class="RktValLink" data-pltdoc="x">guard-evt</a></span>, but when <span class="RktVar">maker</span> is called, it is
given a NACK (“negative acknowledgment”) event. After starting the
call to <span class="RktVar">maker</span>, if the event from <span class="RktVar">maker</span> is not
ultimately chosen as the ready event, then the NACK event supplied to
<span class="RktVar">maker</span> becomes <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a> with a
<a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=guide&rel=void_undefined.html&version=6.1" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<void></span></span></a> value.</div></p><p>The NACK event becomes <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a> when the event
is abandoned when either some other event is chosen, the synchronizing
thread is dead, or control escapes from the call to <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span>
(even if <span class="RktVar">nack-guard</span>’s <span class="RktVar">maker</span> has not yet returned a
value). If the event returned by <span class="RktVar">maker</span> is chosen, then the
NACK event never becomes <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a>.</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)._poll-guard-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._poll-guard-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">poll-guard-evt</a></span></span><span class="hspace"> </span><span class="RktVar">maker</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%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">maker</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</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><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="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Like <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._guard-evt%29%29" class="RktValLink" data-pltdoc="x">guard-evt</a></span>, but when <span class="RktVar">maker</span> is called, it is
provided a boolean value that indicates whether the event will be used
for a poll, <span class="RktVal">#t</span>, or for a blocking synchronization,
<span class="RktVal">#f</span>.</div></p><p>If <span class="RktVal">#t</span> is supplied to <span class="RktVar">maker</span>, if breaks are
disabled, if the polling thread is not terminated, and if polling the
resulting event produces a <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a>, then the event
will certainly be chosen for its 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>value</p></div></div><p class="RForeground"><a name="(def._((quote._~23~25kernel)._always-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._always-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">always-evt</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A constant event that is always <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready
for synchronization</span></a>, with itself as its <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a>.</div></p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Example:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._always-evt%29%29" class="RktValLink" data-pltdoc="x">always-evt</a></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<always-evt></span></p></td></tr></table></blockquote></td></tr></table></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>value</p></div></div><p class="RForeground"><a name="(def._((quote._~23~25kernel)._never-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._never-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">never-evt</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A constant event that is never <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready
for synchronization</span></a>.</div></p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Example:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span><span class="hspace"> </span><span class="RktVal">0.1</span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._never-evt%29%29" class="RktValLink" data-pltdoc="x">never-evt</a></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr></table></blockquote></td></tr></table></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)._system-idle-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._system-idle-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">system-idle-evt</a></span></span><span class="RktPn"></span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Returns an event that is <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a> when the
system is otherwise idle: if the result event were replaced by
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._never-evt%29%29" class="RktValLink" data-pltdoc="x">never-evt</a></span>, no thread in the system would be available to run.
In other words, all threads must be suspended or blocked on events
with timeouts that have not yet expired. The system-idle event’s
<a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> is <a href="http://download.racket-lang.org/docs/6.1/html/local-redirect/index.html?doc=guide&rel=void_undefined.html&version=6.1" class="RktModLink Sq" data-pltdoc="x"><span class="nobreak"><span class="RktRes">#<void></span></span></a>. The result of the
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._system-idle-evt%29%29" class="RktValLink" data-pltdoc="x">system-idle-evt</a></span> procedure is always the same event.</div></p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </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="RktSym">th</span><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._~ce~bb%29%29" class="RktStxLink" data-pltdoc="x">λ</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><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="hspace"> </span><span class="RktPn">(</span><span class="RktSym">loop</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><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span><span class="hspace"> </span><span class="RktVal">0.1</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._system-idle-evt%29%29" class="RktValLink" data-pltdoc="x">system-idle-evt</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="threads.html#%28def._%28%28quote._~23~25kernel%29._kill-thread%29%29" class="RktValLink" data-pltdoc="x">kill-thread</a></span><span class="hspace"> </span><span class="RktSym">th</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._system-idle-evt%29%29" class="RktValLink" data-pltdoc="x">system-idle-evt</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr></table></blockquote></td></tr></table></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)._alarm-evt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._alarm-evt%29%29" class="RktValDef RktValLink" data-pltdoc="x">alarm-evt</a></span></span><span class="hspace"> </span><span class="RktVar">msecs</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="#%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">msecs</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a <a href="#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable event</span></a> that is not <a href="#%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="time.html#%28def._%28%28quote._~23~25kernel%29._current-inexact-milliseconds%29%29" class="RktValLink" data-pltdoc="x">current-inexact-milliseconds</a></span><span class="RktPn">)</span> would return a value that is
less than <span class="RktVar">msecs</span>, and it is <a href="#%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="time.html#%28def._%28%28quote._~23~25kernel%29._current-inexact-milliseconds%29%29" class="RktValLink" data-pltdoc="x">current-inexact-milliseconds</a></span><span class="RktPn">)</span> would return a value that is
more than <span class="RktVar">msecs</span>. The <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> of a alarm event is the alarm event itself.</div></p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </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="RktSym">alarm</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._alarm-evt%29%29" class="RktValLink" data-pltdoc="x">alarm-evt</a></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="RktPn">(</span><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><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVal">100</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span><span class="hspace"> </span><span class="RktSym">alarm</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<alarm-evt></span></p></td></tr></table></blockquote></td></tr></table></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)._handle-evt~3f))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">handle-evt?</a></span></span><span class="hspace"> </span><span class="RktVar">evt</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">evt</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._evt~3f%29%29" class="RktValLink" data-pltdoc="x">evt?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">evt</span> was created by <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt%29%29" class="RktValLink" data-pltdoc="x">handle-evt</a></span>
or by <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29" class="RktValLink" data-pltdoc="x">choice-evt</a></span> applied to another event for which
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt~3f%29%29" class="RktValLink" data-pltdoc="x">handle-evt?</a></span> produces <span class="RktVal">#t</span>. For any other event,
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt~3f%29%29" class="RktValLink" data-pltdoc="x">handle-evt?</a></span> produces <span class="RktVal">#f</span>.</div></p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt~3f%29%29" class="RktValLink" data-pltdoc="x">handle-evt?</a></span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._never-evt%29%29" class="RktValLink" data-pltdoc="x">never-evt</a></span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt~3f%29%29" class="RktValLink" data-pltdoc="x">handle-evt?</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._handle-evt%29%29" class="RktValLink" data-pltdoc="x">handle-evt</a></span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._always-evt%29%29" class="RktValLink" data-pltdoc="x">always-evt</a></span><span class="hspace"> </span><span class="RktSym"><a href="values.html#%28def._%28%28quote._~23~25kernel%29._values%29%29" class="RktValLink" data-pltdoc="x">values</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#t</span></p></td></tr></table></blockquote></td></tr></table></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>value</p></div></div><p class="RForeground"><a name="(def._((quote._~23~25kernel)._prop~3aevt))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._prop~3aevt%29%29" class="RktValDef RktValLink" data-pltdoc="x">prop:evt</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="structprops.html#%28def._%28%28quote._~23~25kernel%29._struct-type-property~3f%29%29" class="RktValLink" data-pltdoc="x">struct-type-property?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="structprops.html#%28tech._structure._type._property%29" class="techoutside" data-pltdoc="x"><span class="techinside">structure type property</span></a> that identifies structure types whose
instances can serve as <a href="#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable events</span></a>. The property value can
be any of the following:</div></p><ul><li><p>An event <span class="RktVar">evt</span>: In this case, using the structure as an
event is equivalent to using <span class="RktVar">evt</span>.</p></li><li><p>A procedure <span class="RktVar">proc</span> of one argument: In this case, the
structure is similar to an event generated
by <span class="RktSym"><a href="#%28def._%28%28lib._racket%2Fprivate%2Fmisc..rkt%29._guard-evt%29%29" class="RktValLink" data-pltdoc="x">guard-evt</a></span>, except that the would-be guard
procedure <span class="RktVar">proc</span> receives the structure as an argument, instead
of no arguments; also, a non-event result from <span class="RktVar">proc</span>
is replaced with an event that is already <a href="#%28tech._ready._for._synchronization%29" class="techoutside" data-pltdoc="x"><span class="techinside">ready for synchronization</span></a>
and whose <a href="#%28tech._synchronization._result%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronization result</span></a> is the structure.</p></li><li><p>An exact, non-negative integer between <span class="RktVal">0</span> (inclusive)
and the number of non-automatic fields in the structure type
(exclusive, not counting supertype fields): The integer identifies a
field in the structure, and the field must be designated as
immutable. If the field contains an object or an event-generating
procedure of one argument, the event or procedure is used as
above. Otherwise, the structure acts as an event that is never
ready.</p></li></ul><p>Instances of a structure type with the <span class="RktSym"><a href="portstructs.html#%28def._%28%28quote._~23~25kernel%29._prop~3ainput-port%29%29" class="RktValLink" data-pltdoc="x">prop:input-port</a></span> or
<span class="RktSym"><a href="portstructs.html#%28def._%28%28quote._~23~25kernel%29._prop~3aoutput-port%29%29" class="RktValLink" data-pltdoc="x">prop:output-port</a></span> property are also <a href="#%28tech._synchronizable._event%29" class="techoutside" data-pltdoc="x"><span class="techinside">synchronizable events</span></a> by virtue
of being a port. If the structure type has more than one of
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._prop~3aevt%29%29" class="RktValLink" data-pltdoc="x">prop:evt</a></span>, <span class="RktSym"><a href="portstructs.html#%28def._%28%28quote._~23~25kernel%29._prop~3ainput-port%29%29" class="RktValLink" data-pltdoc="x">prop:input-port</a></span>, and
<span class="RktSym"><a href="portstructs.html#%28def._%28%28quote._~23~25kernel%29._prop~3aoutput-port%29%29" class="RktValLink" data-pltdoc="x">prop:output-port</a></span>, then the <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._prop~3aevt%29%29" class="RktValLink" data-pltdoc="x">prop:evt</a></span> value (if any)
takes precedence for determining the instance’s behavior as an event,
and the <span class="RktSym"><a href="portstructs.html#%28def._%28%28quote._~23~25kernel%29._prop~3ainput-port%29%29" class="RktValLink" data-pltdoc="x">prop:input-port</a></span> property takes precedence over
<span class="RktSym"><a href="portstructs.html#%28def._%28%28quote._~23~25kernel%29._prop~3aoutput-port%29%29" class="RktValLink" data-pltdoc="x">prop:output-port</a></span> for synchronization.</p><p><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><p>Examples:</p></td></tr><tr><td><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-struct%29%29" class="RktStxLink" data-pltdoc="x">define-struct</a></span><span class="hspace"> </span><span class="RktSym">wt</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">base</span><span class="hspace"> </span><span class="RktSym">val</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">#:property</span><span class="hspace"> </span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._prop~3aevt%29%29" class="RktValLink" data-pltdoc="x">prop:evt</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct-field-index%29%29" class="RktStxLink" data-pltdoc="x">struct-field-index</a></span><span class="hspace"> </span><span class="RktSym">base</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </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="RktSym">sema</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="semaphore.html#%28def._%28%28quote._~23~25kernel%29._make-semaphore%29%29" class="RktValLink" data-pltdoc="x">make-semaphore</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-wt</span><span class="hspace"> </span><span class="RktSym">sema</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="semaphore.html#%28def._%28%28quote._~23~25kernel%29._semaphore-post%29%29" class="RktValLink" data-pltdoc="x">semaphore-post</a></span><span class="hspace"> </span><span class="RktSym">sema</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-wt</span><span class="hspace"> </span><span class="RktSym">sema</span><span class="hspace"> </span><span class="RktVal">#f</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<semaphore></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="semaphore.html#%28def._%28%28quote._~23~25kernel%29._semaphore-post%29%29" class="RktValLink" data-pltdoc="x">semaphore-post</a></span><span class="hspace"> </span><span class="RktSym">sema</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-wt</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="RktSym">self</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">wt-val</span><span class="hspace"> </span><span class="RktSym">self</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">sema</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<semaphore></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="semaphore.html#%28def._%28%28quote._~23~25kernel%29._semaphore-post%29%29" class="RktValLink" data-pltdoc="x">semaphore-post</a></span><span class="hspace"> </span><span class="RktSym">sema</span><span class="RktPn">)</span></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></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="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">my-wt</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">make-wt</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="RktSym">self</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._wrap-evt%29%29" class="RktValLink" data-pltdoc="x">wrap-evt</a></span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">wt-val</span><span class="hspace"> </span><span class="RktSym">self</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </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="RktSym">x</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym">self</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktSym">sema</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><table cellspacing="0" cellpadding="0"><tr><td></td></tr></table></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktSym">my-wt</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#<wt></span></p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%2Ftimeout%29%29" class="RktValLink" data-pltdoc="x">sync/timeout</a></span><span class="hspace"> </span><span class="RktVal">0</span><span class="hspace"> </span><span class="RktSym">my-wt</span><span class="RktPn">)</span></td></tr><tr><td><p><span class="RktRes">#f</span></p></td></tr></table></blockquote></td></tr></table></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>parameter</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((quote._~23~25kernel)._current-evt-pseudo-random-generator))"></a><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._current-evt-pseudo-random-generator%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-evt-pseudo-random-generator</a></span></span><span class="RktPn"></span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._pseudo-random-generator~3f%29%29" class="RktValLink" data-pltdoc="x">pseudo-random-generator?</a></span></td></tr><tr><td><span class="RktPn">(</span><span title="Provided from: racket/base, racket | Package: base"><span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._current-evt-pseudo-random-generator%29%29" class="RktValDef RktValLink" data-pltdoc="x">current-evt-pseudo-random-generator</a></span></span><span class="hspace"> </span><span class="RktVar">generator</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></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">generator</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="generic-numbers.html#%28def._%28%28quote._~23~25kernel%29._pseudo-random-generator~3f%29%29" class="RktValLink" data-pltdoc="x">pseudo-random-generator?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="eval-model.html#%28tech._parameter%29" class="techoutside" data-pltdoc="x"><span class="techinside">parameter</span></a> that determines the pseudo-random number generator used by
<span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._sync%29%29" class="RktValLink" data-pltdoc="x">sync</a></span> for events created by <span class="RktSym"><a href="#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29" class="RktValLink" data-pltdoc="x">choice-evt</a></span>.</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, "6.1", "../");" 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="all-sync.html" title="backward to "11.2 Synchronization"" data-pltdoc="x">← prev</a> <a href="all-sync.html" title="up to "11.2 Synchronization"" data-pltdoc="x">up</a> <a href="channel.html" title="forward to "11.2.2 Channels"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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