doc/core/howto/time.html

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   3 <title>Twisted Documentation: Scheduling tasks for the future</title>
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   8     <h1 class="title">Scheduling tasks for the future</h1>
   9     <div class="toc"><ol/></div>
  10     <div class="content">
  11     <span/>
  12
  13     <p>Let's say we want to run a task X seconds in the future.
  14     The way to do that is defined in the reactor interface <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.internet.interfaces.IReactorTime.html" title="twisted.internet.interfaces.IReactorTime">twisted.internet.interfaces.IReactorTime</a></code>:</p>
  15 <pre class="python"><p class="py-linenumber">1
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  24 </p><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">reactor</span>
  25
  26 <span class="py-src-keyword">def</span> <span class="py-src-identifier">f</span>(<span class="py-src-parameter">s</span>):
  27     <span class="py-src-keyword">print</span> <span class="py-src-string">&quot;this will run 3.5 seconds after it was scheduled: %s&quot;</span> % <span class="py-src-variable">s</span>
  28
  29 <span class="py-src-variable">reactor</span>.<span class="py-src-variable">callLater</span>(<span class="py-src-number">3.5</span>, <span class="py-src-variable">f</span>, <span class="py-src-string">&quot;hello, world&quot;</span>)
  30
  31 <span class="py-src-comment"># f() will only be called if the event loop is started.</span>
  32 <span class="py-src-variable">reactor</span>.<span class="py-src-variable">run</span>()
  33 </pre>
  34
  35     <p>If the result of the function is important or if it may be necessary
  36     to handle exceptions it raises, then the <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.internet.task.deferLater.html" title="twisted.internet.task.deferLater">twisted.internet.task.deferLater</a></code> utility conveniently
  37     takes care of creating a <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.internet.defer.Deferred.html" title="twisted.internet.defer.Deferred">Deferred</a></code> and setting up a delayed
  38     call:</p>
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  52 </p><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">task</span>
  53 <span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">reactor</span>
  54
  55 <span class="py-src-keyword">def</span> <span class="py-src-identifier">f</span>(<span class="py-src-parameter">s</span>):
  56     <span class="py-src-keyword">return</span> <span class="py-src-string">&quot;This will run 3.5 seconds after it was scheduled: %s&quot;</span> % <span class="py-src-variable">s</span>
  57
  58 <span class="py-src-variable">d</span> = <span class="py-src-variable">task</span>.<span class="py-src-variable">deferLater</span>(<span class="py-src-variable">reactor</span>, <span class="py-src-number">3.5</span>, <span class="py-src-variable">f</span>, <span class="py-src-string">&quot;hello, world&quot;</span>)
  59 <span class="py-src-keyword">def</span> <span class="py-src-identifier">called</span>(<span class="py-src-parameter">result</span>):
  60     <span class="py-src-keyword">print</span> <span class="py-src-variable">result</span>
  61 <span class="py-src-variable">d</span>.<span class="py-src-variable">addCallback</span>(<span class="py-src-variable">called</span>)
  62
  63 <span class="py-src-comment"># f() will only be called if the event loop is started.</span>
  64 <span class="py-src-variable">reactor</span>.<span class="py-src-variable">run</span>()
  65 </pre>
  66
  67     <p>If we want a task to run every X seconds repeatedly, we can
  68     use <code class="API"><a href="http://twistedmatrix.com/documents/12.1.0/api/twisted.internet.task.LoopingCall.html" title="twisted.internet.task.LoopingCall">twisted.internet.task.LoopingCall</a></code>:</p>
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  80 </p><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">task</span>
  81 <span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">reactor</span>
  82
  83 <span class="py-src-keyword">def</span> <span class="py-src-identifier">runEverySecond</span>():
  84     <span class="py-src-keyword">print</span> <span class="py-src-string">&quot;a second has passed&quot;</span>
  85
  86 <span class="py-src-variable">l</span> = <span class="py-src-variable">task</span>.<span class="py-src-variable">LoopingCall</span>(<span class="py-src-variable">runEverySecond</span>)
  87 <span class="py-src-variable">l</span>.<span class="py-src-variable">start</span>(<span class="py-src-number">1.0</span>) <span class="py-src-comment"># call every second</span>
  88
  89 <span class="py-src-comment"># l.stop() will stop the looping calls</span>
  90 <span class="py-src-variable">reactor</span>.<span class="py-src-variable">run</span>()
  91 </pre>
  92
  93     <p>If we want to cancel a task that we've scheduled:</p>
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 102 </p><span class="py-src-keyword">from</span> <span class="py-src-variable">twisted</span>.<span class="py-src-variable">internet</span> <span class="py-src-keyword">import</span> <span class="py-src-variable">reactor</span>
 103
 104 <span class="py-src-keyword">def</span> <span class="py-src-identifier">f</span>():
 105     <span class="py-src-keyword">print</span> <span class="py-src-string">&quot;I'll never run.&quot;</span>
 106
 107 <span class="py-src-variable">callID</span> = <span class="py-src-variable">reactor</span>.<span class="py-src-variable">callLater</span>(<span class="py-src-number">5</span>, <span class="py-src-variable">f</span>)
 108 <span class="py-src-variable">callID</span>.<span class="py-src-variable">cancel</span>()
 109 <span class="py-src-variable">reactor</span>.<span class="py-src-variable">run</span>()
 110 </pre>
 111
 112     <p>As with all reactor-based code, in order for scheduling to work the reactor must be started using <code class="python">reactor.run()</code>.</p>
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