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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>11.6 Engines</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">The Racket Reference</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="tocviewli
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can be preempted by a timer or other external trigger. They are
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inspired by the work of Haynes and Friedman [<a href="doc-bibliography.html#%28cite._.Haynes84%29" data-pltdoc="x">Haynes84</a>].</p><p><div class="SIntrapara">Engines log their behavior via a logger with the name
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<span class="RktVal">'</span><span class="RktVal">racket/engine</span>. The logger is created when the module
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is instantiated and uses the result of <span class="RktPn">(</span><span class="RktSym"><a href="logging.html#%28def._%28%28quote._~23~25kernel%29._current-logger%29%29" class="RktValLink" data-pltdoc="x">current-logger</a></span><span class="RktPn">)</span>
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as its parent. The library adds logs a <span class="RktVal">'</span><span class="RktVal">debug</span> level
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message: when <span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</a></span>
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is called, when the engine timeout expires, and when the engine is
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stopped (either because it terminated or it reached a safe point to
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stop). Each log message holds a value of the struct:
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</div><div class="SIntrapara"><blockquote class="SCodeFlow"><p><span class="RktPn">(</span><span class="RktSym"><a href="define-struct.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._struct%29%29" class="RktStxLink" data-pltdoc="x">struct</a></span><span class="hspace"> </span><span class="RktSym">engine-info</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">msec</span><span class="hspace"> </span><span class="RktSym">name</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">#:prefab</span><span class="RktPn">)</span></p></blockquote></div><div class="SIntrapara">where the <span class="RktVar">msec</span> field holds the result of
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<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> at the moment of logging,
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and the <span class="RktVar">name</span> field holds the name of the procedure
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passed to <span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine%29%29" class="RktValLink" data-pltdoc="x">engine</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._((lib._racket/engine..rkt)._engine))"></a><span title="Provided from: racket/engine | Package: base"><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine%29%29" class="RktValDef RktValLink" data-pltdoc="x">engine</a></span></span><span class="hspace"> </span><span class="RktVar">proc</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine~3f%29%29" class="RktValLink" data-pltdoc="x">engine?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">proc</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="hspace"> </span><span class="RktPn">. </span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="RktPn"> .</span><span class="hspace"> </span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void~3f%29%29" class="RktValLink" data-pltdoc="x">void?</a></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="RktPn"> .</span><span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Returns an engine object to encapsulate a thread that runs only when
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allowed. The <span class="RktVar">proc</span> procedure should accept one argument, and
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<span class="RktVar">proc</span> is run in the engine thread when
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<span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</a></span> is called. If <span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</a></span> returns
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due to a timeout, then the engine thread is suspended until a
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future call to <span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</a></span>. Thus, <span class="RktVar">proc</span> only
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executes during the dynamic extent of a <span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</a></span> call.</div></p><p>The argument to <span class="RktVar">proc</span> is a procedure that takes a boolean, and
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it can be used to disable suspends (in case <span class="RktVar">proc</span> has critical
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regions where it should not be suspended). A true value passed to the
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procedure enables suspends, and <span class="RktVal">#f</span> disables
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suspends. Initially, suspends are allowed.</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/engine..rkt)._engine~3f))"></a><span title="Provided from: racket/engine | Package: base"><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine~3f%29%29" class="RktValDef RktValLink" data-pltdoc="x">engine?</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="data-structure-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%29%29" class="RktStxLink" data-pltdoc="x">any</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">v</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns <span class="RktVal">#t</span> if <span class="RktVar">v</span> is an engine produced by
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<span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine%29%29" class="RktValLink" data-pltdoc="x">engine</a></span>, <span class="RktVal">#f</span> otherwise.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/engine..rkt)._engine-run))"></a><span title="Provided from: racket/engine | Package: base"><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValDef RktValLink" data-pltdoc="x">engine-run</a></span></span><span class="hspace"> </span><span class="RktVar">until</span><span class="hspace"> </span><span class="RktVar">engine</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">until</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="sync.html#%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="number-types.html#%28def._%28%28quote._~23~25kernel%29._real~3f%29%29" class="RktValLink" data-pltdoc="x">real?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">engine</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine~3f%29%29" class="RktValLink" data-pltdoc="x">engine?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Allows the thread associated with <span class="RktVar">engine</span> to execute for up
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as long as <span class="RktVar">until</span> milliseconds (if <span class="RktVar">until</span> is a real
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number) or <span class="RktVar">until</span> is ready (if <span class="RktVar">until</span> is an event). If
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<span class="RktVar">engine</span>’s procedure disables suspends, then the engine
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can run arbitrarily long until it re-enables suspends.</div></p><p>The <span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</a></span> procedure returns <span class="RktVal">#t</span> if
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<span class="RktVar">engine</span>’s procedure completes (or if it completed earlier),
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and the result is available via <span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-result%29%29" class="RktValLink" data-pltdoc="x">engine-result</a></span>. The
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<span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</a></span> procedure returns <span class="RktVal">#f</span> if
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<span class="RktVar">engine</span>’s procedure does not complete before it is
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suspended after the <span class="RktVar">until</span> condition is met. If <span class="RktVar">engine</span>’s
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procedure raises an exception, then it is re-raised by
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<span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-run%29%29" class="RktValLink" data-pltdoc="x">engine-run</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._((lib._racket/engine..rkt)._engine-result))"></a><span title="Provided from: racket/engine | Package: base"><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-result%29%29" class="RktValDef RktValLink" data-pltdoc="x">engine-result</a></span></span><span class="hspace"> </span><span class="RktVar">engine</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">engine</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine~3f%29%29" class="RktValLink" data-pltdoc="x">engine?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns the result for <span class="RktVar">engine</span> if it has completed with a
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value (as opposed to an exception), <span class="RktVal">#f</span> otherwise.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/engine..rkt)._engine-kill))"></a><span title="Provided from: racket/engine | Package: base"><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine-kill%29%29" class="RktValDef RktValLink" data-pltdoc="x">engine-kill</a></span></span><span class="hspace"> </span><span class="RktVar">engine</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void~3f%29%29" class="RktValLink" data-pltdoc="x">void?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">engine</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="engine.html#%28def._%28%28lib._racket%2Fengine..rkt%29._engine~3f%29%29" class="RktValLink" data-pltdoc="x">engine?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Forcibly terminates the thread associated with <span class="RktVar">engine</span> if
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it is still running, leaving the engine result unchanged.</div></p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="places.html" title="backward to "11.5 Places"" data-pltdoc="x">← prev</a> <a href="concurrency.html" title="up to "11 Concurrency and Parallelism"" data-pltdoc="x">up</a> <a href="memory-order.html" title="forward to "11.7 Machine Memory Order"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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