Help/Scheduling/Semaphore.html

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  27 <p class="p1"><span class="s1"><b>Semaphore</b></span><span class="s2"><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span></span><b>control parallel execution of threads</b></p>
  28 <p class="p2"><br></p>
  29 <p class="p2"><br></p>
  30 <p class="p1">superclass: Object</p>
  31 <p class="p2"><br></p>
  32 <p class="p2"><br></p>
  33 <p class="p1"><b><span class="Apple-tab-span">  </span>*new(count)<span class="Apple-tab-span"> </span></b>create a new instance, set the maximum number of running threads (default: 1).</p>
  34 <p class="p2"><b><span class="Apple-tab-span">  </span></b></p>
  35 <p class="p1"><b><span class="Apple-tab-span">  </span>count<span class="Apple-tab-span">       </span><span class="Apple-tab-span">    </span></b>determines the number of running threads</p>
  36 <p class="p2"><b><span class="Apple-tab-span">  </span></b></p>
  37 <p class="p1"><b><span class="Apple-tab-span">  </span>clear<span class="Apple-tab-span">       </span><span class="Apple-tab-span">    </span></b>remove any reference to threads, but do not rescedule any pending ones.</p>
  38 <p class="p2"><span class="Apple-tab-span">     </span></p>
  39 <p class="p1"><b><span class="Apple-tab-span">  </span>wait<span class="Apple-tab-span">        </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span></b>stop current thread if already too many are running, otherwise continue.</p>
  40 <p class="p2"><b><span class="Apple-tab-span">  </span><span class="Apple-tab-span">    </span></b></p>
  41 <p class="p1"><b><span class="Apple-tab-span">  </span>signal<span class="Apple-tab-span">      </span><span class="Apple-tab-span">    </span></b>unblock the semaphore, reschedule next pending thread.</p>
  42 <p class="p2"><b><span class="Apple-tab-span">  </span></b></p>
  43 <p class="p3"><br></p>
  44 <p class="p3"><br></p>
  45 <p class="p3"><br></p>
  46 <p class="p4">// example</p>
  47 <p class="p3"><br></p>
  48 <p class="p3"><br></p>
  49 <p class="p4">// allow only one thread</p>
  50 <p class="p5">(</p>
  51 <p class="p6"><span class="s3">c = </span>Semaphore<span class="s3">(1);</span></p>
  52 <p class="p5">fork {<span class="Apple-converted-space"> </span></p>
  53 <p class="p5"><span class="Apple-tab-span">     </span>c.wait;<span class="Apple-converted-space"> </span></p>
  54 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 1&gt; now I am doing something for 10 seconds. Block the semaphore meanwhile."<span class="s3">.postln;<span class="Apple-converted-space"> </span></span></p>
  55 <p class="p5"><span class="Apple-tab-span">     </span>10.wait;</p>
  56 <p class="p5"><span class="Apple-tab-span">     </span>c.signal;</p>
  57 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 1&gt; ok, done. Release the semaphore."<span class="s3">.postln;<span class="Apple-converted-space"> </span></span></p>
  58 <p class="p5">};</p>
  59 <p class="p5">fork {</p>
  60 <p class="p5"><span class="Apple-tab-span">     </span>3.0.rand.wait;</p>
  61 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 2&gt; I would like to go on, if I may."<span class="s3">.postln;</span></p>
  62 <p class="p5"><span class="Apple-tab-span">     </span>c.wait; <span class="s4">// may I?</span></p>
  63 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 2&gt; this took until the other thread has released the semaphore. "</p>
  64 <p class="p7"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>"Blocking for 4 seconds."<span class="s3">.postln;</span></p>
  65 <p class="p5"><span class="Apple-tab-span">     </span>4.wait;</p>
  66 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 2&gt; ok, done. Releasing the semaphore"<span class="s3">.postln;</span></p>
  67 <p class="p5"><span class="Apple-tab-span">     </span>c.signal;</p>
  68 <p class="p5">};</p>
  69 <p class="p5">fork {</p>
  70 <p class="p5"><span class="Apple-tab-span">     </span>4.wait;</p>
  71 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 3&gt; I, too, would like to go on, if I may."<span class="s3">.postln;</span></p>
  72 <p class="p5"><span class="Apple-tab-span">     </span>c.wait; <span class="s4">// may I?</span></p>
  73 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 3&gt; this took until both other threads had released the semaphore."<span class="s3">.postln;</span></p>
  74 <p class="p5"><span class="Apple-tab-span">     </span>c.signal;</p>
  75 <p class="p5">};</p>
  76 <p class="p5">)</p>
  77 <p class="p3"><br></p>
  78 <p class="p3"><br></p>
  79 <p class="p3"><br></p>
  80 <p class="p4">// allow two threads at a time.</p>
  81 <p class="p5">(</p>
  82 <p class="p6"><span class="s3">c = </span>Semaphore<span class="s3">(2);</span></p>
  83 <p class="p5">fork {<span class="Apple-converted-space"> </span></p>
  84 <p class="p5"><span class="Apple-tab-span">     </span>c.wait;<span class="Apple-converted-space"> </span></p>
  85 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 1&gt; now I am doing something for 20 seconds. Block the semaphore."<span class="s3">.postln;<span class="Apple-converted-space"> </span></span></p>
  86 <p class="p5"><span class="Apple-tab-span">     </span>10.wait;</p>
  87 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 1&gt; ok, done. Releasing the semaphore"<span class="s3">.postln;</span></p>
  88 <p class="p5"><span class="Apple-tab-span">     </span>c.signal;</p>
  89 <p class="p3"><span class="Apple-tab-span">     </span><span class="Apple-converted-space"> </span></p>
  90 <p class="p5">};</p>
  91 <p class="p5">fork {</p>
  92 <p class="p5"><span class="Apple-tab-span">     </span>rrand(3.0, 5.0).wait;</p>
  93 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 2&gt; I would like to go on, if I may."<span class="s3">.postln;</span></p>
  94 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span>if(c.count &lt;= 0) { </span>"thread 3&gt; ok, then I wait ..."<span class="s3">.postln };</span></p>
  95 <p class="p5"><span class="Apple-tab-span">     </span>c.wait; <span class="s4">// may I?</span></p>
  96 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 1&gt; ok, going ahead."<span class="s3">.postln;</span></p>
  97 <p class="p5"><span class="Apple-tab-span">     </span>17.wait;</p>
  98 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 2&gt; ok, done. Releasing the semaphore"<span class="s3">.postln;</span></p>
  99 <p class="p5"><span class="Apple-tab-span">     </span>c.signal;</p>
 100 <p class="p5">};</p>
 101 <p class="p5">fork {</p>
 102 <p class="p5"><span class="Apple-tab-span">     </span>6.wait;</p>
 103 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 3&gt; I, too, would like to go on, if I may."<span class="s3">.postln;</span></p>
 104 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span>if(c.count &lt;= 0) { </span>"thread 3&gt; ok, then I wait ..."<span class="s3">.postln };</span></p>
 105 <p class="p5"><span class="Apple-tab-span">     </span>c.wait; <span class="s4">// may I?</span></p>
 106 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 3&gt; ok, this took until the first thread had released the semaphore. "</p>
 107 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span></span>"Ok, doing something for 4 seconds. Block the semaphore"<span class="s3">.postln;</span></p>
 108 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>4.wait;</p>
 109 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"Releasing the semaphore."<span class="s3">.postln;</span></p>
 110 <p class="p5"><span class="Apple-tab-span">     </span>c.signal;</p>
 111 <p class="p3"><span class="Apple-tab-span">     </span></p>
 112 <p class="p5">};</p>
 113 <p class="p5">fork {</p>
 114 <p class="p5"><span class="Apple-tab-span">     </span>7.wait;</p>
 115 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 4&gt; Me, the fourth one, would like to go on, if I may."<span class="s3">.postln;</span></p>
 116 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span>if(c.count &lt;= 0) { </span>"thread 4&gt; ok, then I wait ..."<span class="s3">.postln };</span></p>
 117 <p class="p5"><span class="Apple-tab-span">     </span>c.wait; <span class="s4">// may I?</span></p>
 118 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"thread 4&gt; ok, this took until the third thread had released the semaphore. "</p>
 119 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span></span>"Ok, doing something for 3 seconds. Block the semaphore"<span class="s3">.postln;</span></p>
 120 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>3.wait;</p>
 121 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span></span>"Releasing the semaphore."<span class="s3">.postln;</span></p>
 122 <p class="p5"><span class="Apple-tab-span">     </span>c.signal;</p>
 123 <p class="p5">};</p>
 124 <p class="p3"><br></p>
 125 <p class="p5">)</p>
 126 <p class="p3"><br></p>
 127 <p class="p3"><br></p>
 128 <p class="p4">// grant exclusive access to data to only one thread</p>
 129 <p class="p4">// there should never be mixed values in the data array</p>
 130 <p class="p3"><br></p>
 131 <p class="p5">(</p>
 132 <p class="p5"><span class="s5">var</span> data, useAndModify;</p>
 133 <p class="p3"><br></p>
 134 <p class="p5">data = [1, 2, 3];</p>
 135 <p class="p6"><span class="s3">c = </span>Semaphore<span class="s3">(1);</span></p>
 136 <p class="p4">// c = Semaphore(2); use this to test how it would behave without exclusive access.</p>
 137 <p class="p5">useAndModify = { <span class="s5">|newData, who|</span></p>
 138 <p class="p7"><span class="s3"><span class="Apple-tab-span">    </span>postln(who + </span>"trying to get blocking access."<span class="s3">);</span></p>
 139 <p class="p5"><span class="Apple-tab-span">     </span>if(c.count &lt;= 0) { who + <span class="s6">"ok, then I wait ..."</span>.postln };</p>
 140 <p class="p4"><span class="s3"><span class="Apple-tab-span">    </span>c.wait; </span>// may I access? if not, I wait. if yes, disallow others.</p>
 141 <p class="p5"><span class="Apple-tab-span">     </span><span class="s6">"\n"</span>.post;</p>
 142 <p class="p5"><span class="Apple-tab-span">     </span>(who + <span class="s6">"continuing..."</span>).postln;</p>
 143 <p class="p5"><span class="Apple-tab-span">     </span>data.do({ <span class="s5">|x|</span></p>
 144 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span>0.1.wait;</p>
 145 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span>postln(who + x);</p>
 146 <p class="p3"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span></p>
 147 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>});</p>
 148 <p class="p5"><span class="Apple-tab-span">     </span><span class="s6">"\n"</span>.post;</p>
 149 <p class="p5"><span class="Apple-tab-span">     </span>newData.do { <span class="s5">|x, i|</span> data[i] = x };</p>
 150 <p class="p5"><span class="Apple-tab-span">     </span>postln(who + <span class="s6">"rewriting data to:"</span> + newData);</p>
 151 <p class="p5"><span class="Apple-tab-span">     </span>postln(who + <span class="s6">"releasing"</span>);</p>
 152 <p class="p4"><span class="s3"><span class="Apple-tab-span">    </span>c.signal; </span>// allow others access again</p>
 153 <p class="p5">};</p>
 154 <p class="p3"><br></p>
 155 <p class="p4">// e.g. set the values to integers</p>
 156 <p class="p6"><span class="s3">u = </span>Routine<span class="s3"> {</span></p>
 157 <p class="p5"><span class="Apple-tab-span">     </span><span class="s5">inf</span>.do { <span class="s5">|i|</span></p>
 158 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>useAndModify.value([100, 200, 300], <span class="s6">"thread 1&gt;"</span>);</p>
 159 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>rrand(1, 3).wait;</p>
 160 <p class="p5"><span class="Apple-tab-span">     </span>}</p>
 161 <p class="p5">};</p>
 162 <p class="p3"><br></p>
 163 <p class="p4">// e.g. set the values to floats</p>
 164 <p class="p5">k =<span class="Apple-converted-space">  </span><span class="s5">Routine</span> {</p>
 165 <p class="p5"><span class="Apple-tab-span">     </span>0.5.wait;</p>
 166 <p class="p5"><span class="Apple-tab-span">     </span><span class="s5">inf</span>.do { <span class="s5">|i|</span></p>
 167 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>useAndModify.value([pi, 0.5pi, 2pi], <span class="s6">"thread 2&gt;"</span>);</p>
 168 <p class="p5"><span class="Apple-tab-span">     </span><span class="Apple-tab-span">    </span>rrand(1, 5).wait;</p>
 169 <p class="p5"><span class="Apple-tab-span">     </span>}</p>
 170 <p class="p5">};</p>
 171 <p class="p5">u.play;</p>
 172 <p class="p5">k.play;</p>
 173 <p class="p5">);</p>
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