doc/guide/localhost/MLtonThread

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  22 <a href="./Home">MLton 20180207</a>
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  25 <div id="header">
  26 <h1>MLtonThread</h1>
  27 </div>
  28 <div id="content">
  29 <div id="preamble">
  30 <div class="sectionbody">
  31 <div class="listingblock">
  32 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">MLTON_THREAD</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  33 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
  34 <span class="w">      </span><span class="k">structure</span><span class="w"> </span><span class="n">AtomicState</span><span class="p">:</span><span class="w"></span>
  35 <span class="w">         </span><span class="k">sig</span><span class="w"></span>
  36 <span class="w">            </span><span class="k">datatype</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">NonAtomic</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Atomic</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">int</span><span class="w"></span>
  37 <span class="w">         </span><span class="k">end</span><span class="w"></span>
  38
  39 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">atomically</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"></span>
  40 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">atomicBegin</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
  41 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">atomicEnd</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
  42 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">atomicState</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">AtomicState</span><span class="p">.</span><span class="n">t</span><span class="w"></span>
  43
  44 <span class="w">      </span><span class="k">structure</span><span class="w"> </span><span class="n">Runnable</span><span class="p">:</span><span class="w"></span>
  45 <span class="w">         </span><span class="k">sig</span><span class="w"></span>
  46 <span class="w">            </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  47 <span class="w">         </span><span class="k">end</span><span class="w"></span>
  48
  49 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  50
  51 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">atomicSwitch</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"></span>
  52 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">new</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  53 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">prepend</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;b</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;b</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  54 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">prepare</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"></span>
  55 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">switch</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"></span>
  56 <span class="w">   </span><span class="k">end</span><span class="w"></span>
  57 </pre></div></div></div>
  58 <div class="paragraph"><p><span class="monospaced">MLton.Thread</span> provides access to MLton&#8217;s user-level thread
  59 implementation (i.e. not OS-level threads).  Threads are lightweight
  60 data structures that represent a paused computation.  Runnable threads
  61 are threads that will begin or continue computing when <span class="monospaced">switch</span>-ed to.
  62 <span class="monospaced">MLton.Thread</span> does not include a default scheduling mechanism, but it
  63 can be used to implement both preemptive and non-preemptive threads.</p></div>
  64 <div class="ulist"><ul>
  65 <li>
  66 <p>
  67 <span class="monospaced">type AtomicState.t</span>
  68 </p>
  69 <div class="paragraph"><p>the type of atomic states.</p></div>
  70 </li>
  71 <li>
  72 <p>
  73 <span class="monospaced">atomically f</span>
  74 </p>
  75 <div class="paragraph"><p>runs <span class="monospaced">f</span> in a critical section.</p></div>
  76 </li>
  77 <li>
  78 <p>
  79 <span class="monospaced">atomicBegin ()</span>
  80 </p>
  81 <div class="paragraph"><p>begins a critical section.</p></div>
  82 </li>
  83 <li>
  84 <p>
  85 <span class="monospaced">atomicEnd ()</span>
  86 </p>
  87 <div class="paragraph"><p>ends a critical section.</p></div>
  88 </li>
  89 <li>
  90 <p>
  91 <span class="monospaced">atomicState ()</span>
  92 </p>
  93 <div class="paragraph"><p>returns the current atomic state.</p></div>
  94 </li>
  95 <li>
  96 <p>
  97 <span class="monospaced">type Runnable.t</span>
  98 </p>
  99 <div class="paragraph"><p>the type of threads that can be resumed.</p></div>
 100 </li>
 101 <li>
 102 <p>
 103 <span class="monospaced">type 'a t</span>
 104 </p>
 105 <div class="paragraph"><p>the type of threads that expect a value of type <span class="monospaced">'a</span>.</p></div>
 106 </li>
 107 <li>
 108 <p>
 109 <span class="monospaced">atomicSwitch f</span>
 110 </p>
 111 <div class="paragraph"><p>like <span class="monospaced">switch</span>, but assumes an atomic calling context.  Upon
 112 <span class="monospaced">switch</span>-ing back to the current thread, an implicit <span class="monospaced">atomicEnd</span> is
 113 performed.</p></div>
 114 </li>
 115 <li>
 116 <p>
 117 <span class="monospaced">new f</span>
 118 </p>
 119 <div class="paragraph"><p>creates a new thread that, when run, applies <span class="monospaced">f</span> to the value given to
 120 the thread.  <span class="monospaced">f</span> must terminate by `switch`ing to another thread or
 121 exiting the process.</p></div>
 122 </li>
 123 <li>
 124 <p>
 125 <span class="monospaced">prepend (t, f)</span>
 126 </p>
 127 <div class="paragraph"><p>creates a new thread (destroying <span class="monospaced">t</span> in the process) that first
 128 applies <span class="monospaced">f</span> to the value given to the thread and then continues with
 129 <span class="monospaced">t</span>.  This is a constant time operation.</p></div>
 130 </li>
 131 <li>
 132 <p>
 133 <span class="monospaced">prepare (t, v)</span>
 134 </p>
 135 <div class="paragraph"><p>prepares a new runnable thread (destroying <span class="monospaced">t</span> in the process) that
 136 will evaluate <span class="monospaced">t</span> on <span class="monospaced">v</span>.</p></div>
 137 </li>
 138 <li>
 139 <p>
 140 <span class="monospaced">switch f</span>
 141 </p>
 142 <div class="paragraph"><p>applies <span class="monospaced">f</span> to the current thread to get <span class="monospaced">rt</span>, and then start running
 143 thread <span class="monospaced">rt</span>.  It is an error for <span class="monospaced">f</span> to perform another <span class="monospaced">switch</span>.  <span class="monospaced">f</span>
 144 is guaranteed to run atomically.</p></div>
 145 </li>
 146 </ul></div>
 147 </div>
 148 </div>
 149 <div class="sect1">
 150 <h2 id="_example_of_non_preemptive_threads">Example of non-preemptive threads</h2>
 151 <div class="sectionbody">
 152 <div class="listingblock">
 153 <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">Queue</span><span class="p">:</span><span class="w"></span>
 154 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
 155 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 156
 157 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">new</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 158 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">enque</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 159 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">deque</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">option</span><span class="w"></span>
 160 <span class="w">   </span><span class="k">end</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 161 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
 162 <span class="w">      </span><span class="k">datatype</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">{</span><span class="n">front</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="n">ref</span><span class="p">,</span><span class="w"> </span><span class="n">back</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="n">ref</span><span class="p">}</span><span class="w"></span>
 163
 164 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">new</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">{</span><span class="n">front</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">[],</span><span class="w"> </span><span class="n">back</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">[]}</span><span class="w"></span>
 165
 166 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">enque</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="p">{</span><span class="n">back</span><span class="p">,</span><span class="w"> </span><span class="p">...},</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">back</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">!back</span><span class="w"></span>
 167
 168 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">deque</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="p">{</span><span class="n">front</span><span class="p">,</span><span class="w"> </span><span class="n">back</span><span class="p">})</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 169 <span class="w">         </span><span class="k">case</span><span class="w"> </span><span class="n">!front</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 170 <span class="w">            </span><span class="p">[]</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="k">case</span><span class="w"> </span><span class="n">!back</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 171 <span class="w">                      </span><span class="p">[]</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">NONE</span><span class="w"></span>
 172 <span class="w">                    </span><span class="p">|</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">rev</span><span class="w"> </span><span class="n">l</span><span class="w"></span>
 173 <span class="w">                           </span><span class="k">in</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 174 <span class="w">                              </span><span class="p">[]</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="k">raise</span><span class="w"> </span><span class="n">Fail</span><span class="w"> </span><span class="s">&quot;deque&quot;</span><span class="w"></span>
 175 <span class="w">                            </span><span class="p">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">back</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="p">[];</span><span class="w"> </span><span class="n">front</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">l</span><span class="p">;</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"></span>
 176 <span class="w">                           </span><span class="k">end</span><span class="p">)</span><span class="w"></span>
 177 <span class="w">          </span><span class="p">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">front</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">l</span><span class="p">;</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"></span>
 178 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 179
 180 <span class="k">structure</span><span class="w"> </span><span class="n">Thread</span><span class="p">:</span><span class="w"></span>
 181 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
 182 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">exit</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"></span>
 183 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">run</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 184 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">spawn</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 185 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">yield</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 186 <span class="w">   </span><span class="k">end</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 187 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
 188 <span class="w">      </span><span class="k">open</span><span class="w"> </span><span class="n">MLton</span><span class="w"></span>
 189 <span class="w">      </span><span class="k">open</span><span class="w"> </span><span class="n">Thread</span><span class="w"></span>
 190
 191 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">topLevel</span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">option</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="n">NONE</span><span class="w"></span>
 192
 193 <span class="w">      </span><span class="k">local</span><span class="w"></span>
 194 <span class="w">         </span><span class="k">val</span><span class="w"> </span><span class="n">threads</span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">Queue</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Queue</span><span class="p">.</span><span class="n">new</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 195 <span class="w">      </span><span class="k">in</span><span class="w"></span>
 196 <span class="w">         </span><span class="k">fun</span><span class="w"> </span><span class="n">ready</span><span class="w"> </span><span class="p">(</span><span class="n">t</span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 197 <span class="w">            </span><span class="n">Queue</span><span class="p">.</span><span class="n">enque</span><span class="p">(</span><span class="n">threads</span><span class="p">,</span><span class="w"> </span><span class="n">t</span><span class="p">)</span><span class="w"></span>
 198 <span class="w">         </span><span class="k">fun</span><span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 199 <span class="w">            </span><span class="k">case</span><span class="w"> </span><span class="n">Queue</span><span class="p">.</span><span class="n">deque</span><span class="w"> </span><span class="n">threads</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 200 <span class="w">               </span><span class="n">NONE</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">valOf</span><span class="w"> </span><span class="p">(</span><span class="n">!topLevel</span><span class="p">)</span><span class="w"></span>
 201 <span class="w">             </span><span class="p">|</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 202 <span class="w">      </span><span class="k">end</span><span class="w"></span>
 203
 204 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">exit</span><span class="w"> </span><span class="p">():</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">switch</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="p">())</span><span class="w"></span>
 205
 206 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">new</span><span class="w"> </span><span class="p">(</span><span class="n">f</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="p">):</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 207 <span class="w">         </span><span class="n">Thread</span><span class="p">.</span><span class="n">prepare</span><span class="w"></span>
 208 <span class="w">         </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">new</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">((</span><span class="n">f</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="k">handle</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">exit</span><span class="w"> </span><span class="p">())</span><span class="w"></span>
 209 <span class="w">                                </span><span class="p">;</span><span class="w"> </span><span class="n">exit</span><span class="w"> </span><span class="p">())),</span><span class="w"></span>
 210 <span class="w">          </span><span class="p">())</span><span class="w"></span>
 211
 212 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">schedule</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">ready</span><span class="w"> </span><span class="n">t</span><span class="p">;</span><span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="p">())</span><span class="w"></span>
 213
 214 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">yield</span><span class="w"> </span><span class="p">():</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">switch</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">schedule</span><span class="w"> </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">prepare</span><span class="w"> </span><span class="p">(</span><span class="n">t</span><span class="p">,</span><span class="w"> </span><span class="p">())))</span><span class="w"></span>
 215
 216 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">spawn</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ready</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">new</span><span class="w"></span>
 217
 218 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">run</span><span class="p">():</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 219 <span class="w">         </span><span class="p">(</span><span class="n">switch</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"></span>
 220 <span class="w">                  </span><span class="p">(</span><span class="n">topLevel</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">prepare</span><span class="w"> </span><span class="p">(</span><span class="n">t</span><span class="p">,</span><span class="w"> </span><span class="p">()))</span><span class="w"></span>
 221 <span class="w">                   </span><span class="p">;</span><span class="w"> </span><span class="n">next</span><span class="p">()))</span><span class="w"></span>
 222 <span class="w">          </span><span class="p">;</span><span class="w"> </span><span class="n">topLevel</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">NONE</span><span class="p">)</span><span class="w"></span>
 223 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 224
 225 <span class="k">val</span><span class="w"> </span><span class="k">rec</span><span class="w"> </span><span class="n">loop</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 226 <span class="w">   </span><span class="k">fn</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 227 <span class="w">    </span><span class="p">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">print</span><span class="p">(</span><span class="n">concat</span><span class="p">[</span><span class="n">Int</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="n">n</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">])</span><span class="w"></span>
 228 <span class="w">            </span><span class="p">;</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">yield</span><span class="p">()</span><span class="w"></span>
 229 <span class="w">            </span><span class="p">;</span><span class="w"> </span><span class="n">loop</span><span class="p">(</span><span class="n">n</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="mi">1</span><span class="p">))</span><span class="w"></span>
 230
 231 <span class="k">val</span><span class="w"> </span><span class="k">rec</span><span class="w"> </span><span class="n">loop&#39;</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 232 <span class="w">   </span><span class="k">fn</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 233 <span class="w">    </span><span class="p">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">spawn</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">loop</span><span class="w"> </span><span class="n">n</span><span class="p">);</span><span class="w"> </span><span class="n">loop&#39;</span><span class="w"> </span><span class="p">(</span><span class="n">n</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="mi">2</span><span class="p">))</span><span class="w"></span>
 234
 235 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">spawn</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">loop&#39;</span><span class="w"> </span><span class="mi">10</span><span class="p">)</span><span class="w"></span>
 236
 237 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">run</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 238
 239 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="s">&quot;success</span><span class="se">\n</span><span class="s">&quot;</span><span class="w"></span>
 240 </pre></div></div></div>
 241 </div>
 242 </div>
 243 <div class="sect1">
 244 <h2 id="_example_of_preemptive_threads">Example of preemptive threads</h2>
 245 <div class="sectionbody">
 246 <div class="listingblock">
 247 <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">Queue</span><span class="p">:</span><span class="w"></span>
 248 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
 249 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 250
 251 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">new</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 252 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">enque</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 253 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">deque</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">option</span><span class="w"></span>
 254 <span class="w">   </span><span class="k">end</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 255 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
 256 <span class="w">      </span><span class="k">datatype</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">{</span><span class="n">front</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="n">ref</span><span class="p">,</span><span class="w"> </span><span class="n">back</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="n">ref</span><span class="p">}</span><span class="w"></span>
 257
 258 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">new</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">{</span><span class="n">front</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">[],</span><span class="w"> </span><span class="n">back</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">[]}</span><span class="w"></span>
 259
 260 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">enque</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="p">{</span><span class="n">back</span><span class="p">,</span><span class="w"> </span><span class="p">...},</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">back</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">!back</span><span class="w"></span>
 261
 262 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">deque</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="p">{</span><span class="n">front</span><span class="p">,</span><span class="w"> </span><span class="n">back</span><span class="p">})</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 263 <span class="w">         </span><span class="k">case</span><span class="w"> </span><span class="n">!front</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 264 <span class="w">            </span><span class="p">[]</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="k">case</span><span class="w"> </span><span class="n">!back</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 265 <span class="w">                      </span><span class="p">[]</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">NONE</span><span class="w"></span>
 266 <span class="w">                    </span><span class="p">|</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">rev</span><span class="w"> </span><span class="n">l</span><span class="w"></span>
 267 <span class="w">                           </span><span class="k">in</span><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 268 <span class="w">                              </span><span class="p">[]</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="k">raise</span><span class="w"> </span><span class="n">Fail</span><span class="w"> </span><span class="s">&quot;deque&quot;</span><span class="w"></span>
 269 <span class="w">                            </span><span class="p">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">back</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="p">[];</span><span class="w"> </span><span class="n">front</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">l</span><span class="p">;</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"></span>
 270 <span class="w">                           </span><span class="k">end</span><span class="p">)</span><span class="w"></span>
 271 <span class="w">          </span><span class="p">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">front</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">l</span><span class="p">;</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"></span>
 272 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 273
 274 <span class="k">structure</span><span class="w"> </span><span class="n">Thread</span><span class="p">:</span><span class="w"></span>
 275 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
 276 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">exit</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"></span>
 277 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">run</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 278 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">spawn</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 279 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">yield</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="w"></span>
 280 <span class="w">   </span><span class="k">end</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 281 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
 282 <span class="w">      </span><span class="k">open</span><span class="w"> </span><span class="n">Posix</span><span class="p">.</span><span class="n">Signal</span><span class="w"></span>
 283 <span class="w">      </span><span class="k">open</span><span class="w"> </span><span class="n">MLton</span><span class="w"></span>
 284 <span class="w">      </span><span class="k">open</span><span class="w"> </span><span class="n">Itimer</span><span class="w"> </span><span class="n">Signal</span><span class="w"> </span><span class="n">Thread</span><span class="w"></span>
 285
 286 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">topLevel</span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">option</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="n">NONE</span><span class="w"></span>
 287
 288 <span class="w">      </span><span class="k">local</span><span class="w"></span>
 289 <span class="w">         </span><span class="k">val</span><span class="w"> </span><span class="n">threads</span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">Queue</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Queue</span><span class="p">.</span><span class="n">new</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 290 <span class="w">      </span><span class="k">in</span><span class="w"></span>
 291 <span class="w">         </span><span class="k">fun</span><span class="w"> </span><span class="n">ready</span><span class="w"> </span><span class="p">(</span><span class="n">t</span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 292 <span class="w">            </span><span class="n">Queue</span><span class="p">.</span><span class="n">enque</span><span class="p">(</span><span class="n">threads</span><span class="p">,</span><span class="w"> </span><span class="n">t</span><span class="p">)</span><span class="w"></span>
 293 <span class="w">         </span><span class="k">fun</span><span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 294 <span class="w">            </span><span class="k">case</span><span class="w"> </span><span class="n">Queue</span><span class="p">.</span><span class="n">deque</span><span class="w"> </span><span class="n">threads</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 295 <span class="w">               </span><span class="n">NONE</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">valOf</span><span class="w"> </span><span class="p">(</span><span class="n">!topLevel</span><span class="p">)</span><span class="w"></span>
 296 <span class="w">             </span><span class="p">|</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 297 <span class="w">      </span><span class="k">end</span><span class="w"></span>
 298
 299 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">exit</span><span class="w"> </span><span class="p">():</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">switch</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="p">())</span><span class="w"></span>
 300
 301 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">new</span><span class="w"> </span><span class="p">(</span><span class="n">f</span><span class="p">:</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">unit</span><span class="p">):</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">Runnable</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 302 <span class="w">         </span><span class="n">Thread</span><span class="p">.</span><span class="n">prepare</span><span class="w"></span>
 303 <span class="w">         </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">new</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">((</span><span class="n">f</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="k">handle</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">exit</span><span class="w"> </span><span class="p">())</span><span class="w"></span>
 304 <span class="w">                                </span><span class="p">;</span><span class="w"> </span><span class="n">exit</span><span class="w"> </span><span class="p">())),</span><span class="w"></span>
 305 <span class="w">          </span><span class="p">())</span><span class="w"></span>
 306
 307 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">schedule</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">ready</span><span class="w"> </span><span class="n">t</span><span class="p">;</span><span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="p">())</span><span class="w"></span>
 308
 309 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">yield</span><span class="w"> </span><span class="p">():</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">switch</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">schedule</span><span class="w"> </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">prepare</span><span class="w"> </span><span class="p">(</span><span class="n">t</span><span class="p">,</span><span class="w"> </span><span class="p">())))</span><span class="w"></span>
 310
 311 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">spawn</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">ready</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">new</span><span class="w"></span>
 312
 313 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">setItimer</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 314 <span class="w">         </span><span class="n">Itimer</span><span class="p">.</span><span class="n">set</span><span class="w"> </span><span class="p">(</span><span class="n">Itimer</span><span class="p">.</span><span class="n">Real</span><span class="p">,</span><span class="w"></span>
 315 <span class="w">                     </span><span class="p">{</span><span class="n">value</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">t</span><span class="p">,</span><span class="w"></span>
 316 <span class="w">                      </span><span class="n">interval</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">t</span><span class="p">})</span><span class="w"></span>
 317
 318 <span class="w">      </span><span class="k">fun</span><span class="w"> </span><span class="n">run</span><span class="w"> </span><span class="p">():</span><span class="w"> </span><span class="n">unit</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 319 <span class="w">         </span><span class="p">(</span><span class="n">switch</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"></span>
 320 <span class="w">                  </span><span class="p">(</span><span class="n">topLevel</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">SOME</span><span class="w"> </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">prepare</span><span class="w"> </span><span class="p">(</span><span class="n">t</span><span class="p">,</span><span class="w"> </span><span class="p">()))</span><span class="w"></span>
 321 <span class="w">                   </span><span class="p">;</span><span class="w"> </span><span class="n">new</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">setHandler</span><span class="w"> </span><span class="p">(</span><span class="n">alrm</span><span class="p">,</span><span class="w"> </span><span class="n">Handler</span><span class="p">.</span><span class="n">handler</span><span class="w"> </span><span class="n">schedule</span><span class="p">)</span><span class="w"></span>
 322 <span class="w">                                    </span><span class="p">;</span><span class="w"> </span><span class="n">setItimer</span><span class="w"> </span><span class="p">(</span><span class="n">Time</span><span class="p">.</span><span class="n">fromMilliseconds</span><span class="w"> </span><span class="mi">20</span><span class="p">)))))</span><span class="w"></span>
 323 <span class="w">          </span><span class="p">;</span><span class="w"> </span><span class="n">setItimer</span><span class="w"> </span><span class="n">Time</span><span class="p">.</span><span class="n">zeroTime</span><span class="w"></span>
 324 <span class="w">          </span><span class="p">;</span><span class="w"> </span><span class="n">ignore</span><span class="w"> </span><span class="n">alrm</span><span class="w"></span>
 325 <span class="w">          </span><span class="p">;</span><span class="w"> </span><span class="n">topLevel</span><span class="w"> </span><span class="n">:=</span><span class="w"> </span><span class="n">NONE</span><span class="p">)</span><span class="w"></span>
 326 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 327
 328 <span class="k">val</span><span class="w"> </span><span class="k">rec</span><span class="w"> </span><span class="n">delay</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 329 <span class="w">   </span><span class="k">fn</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 330 <span class="w">    </span><span class="p">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">delay</span><span class="w"> </span><span class="p">(</span><span class="n">n</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="mi">1</span><span class="p">)</span><span class="w"></span>
 331
 332 <span class="k">val</span><span class="w"> </span><span class="k">rec</span><span class="w"> </span><span class="n">loop</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 333 <span class="w">   </span><span class="k">fn</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 334 <span class="w">    </span><span class="p">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">delay</span><span class="w"> </span><span class="mi">500000</span><span class="p">;</span><span class="w"> </span><span class="n">loop</span><span class="w"> </span><span class="p">(</span><span class="n">n</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="mi">1</span><span class="p">))</span><span class="w"></span>
 335
 336 <span class="k">val</span><span class="w"> </span><span class="k">rec</span><span class="w"> </span><span class="n">loop&#39;</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 337 <span class="w">   </span><span class="k">fn</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 338 <span class="w">    </span><span class="p">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">Thread</span><span class="p">.</span><span class="n">spawn</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">loop</span><span class="w"> </span><span class="n">n</span><span class="p">);</span><span class="w"> </span><span class="n">loop&#39;</span><span class="w"> </span><span class="p">(</span><span class="n">n</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="mi">1</span><span class="p">))</span><span class="w"></span>
 339
 340 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">spawn</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">loop&#39;</span><span class="w"> </span><span class="mi">10</span><span class="p">)</span><span class="w"></span>
 341
 342 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Thread</span><span class="p">.</span><span class="n">run</span><span class="w"> </span><span class="p">()</span><span class="w"></span>
 343
 344 <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="s">&quot;success</span><span class="se">\n</span><span class="s">&quot;</span><span class="w"></span>
 345 </pre></div></div></div>
 346 </div>
 347 </div>
 348 </div>
 349 <div id="footnotes"><hr></div>
 350 <div id="footer">
 351 <div id="footer-text">
 352 </div>
 353 <div id="footer-badges">
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