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<a href="./Home">MLton 20130715</a>
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<h1>MLtonThread</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="listingblock">
<div class="content"><div class="highlight"><pre><span></span><span class="kr">signature</span> <span class="nn">MLTON_THREAD</span> <span class="p">=</span>
   <span class="kr">sig</span>
      <span class="kr">structure</span> <span class="nn">AtomicState</span><span class="p">:</span>
         <span class="kr">sig</span>
            <span class="kr">datatype</span> <span class="kt">t</span> <span class="p">=</span> <span class="nc">NonAtomic</span> <span class="p">|</span> <span class="nc">Atomic</span> <span class="kr">of</span> <span class="n">int</span>
         <span class="kr">end</span>

      <span class="kr">val</span> <span class="nv">atomically</span><span class="p">:</span> <span class="p">(</span><span class="n">unit</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span><span class="p">)</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span>
      <span class="kr">val</span> <span class="nv">atomicBegin</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">atomicEnd</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">atomicState</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="nn">AtomicState</span><span class="p">.</span><span class="n">t</span>

      <span class="kr">structure</span> <span class="nn">Runnable</span><span class="p">:</span>
         <span class="kr">sig</span>
            <span class="kr">type</span> <span class="kt">t</span>
         <span class="kr">end</span>

      <span class="kr">type</span> <span class="nd">&#39;a</span> <span class="kt">t</span>

      <span class="kr">val</span> <span class="nv">atomicSwitch</span><span class="p">:</span> <span class="p">(</span><span class="nd">&#39;a</span> <span class="n">t</span> <span class="p">-&gt;</span> <span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span>
      <span class="kr">val</span> <span class="nv">new</span><span class="p">:</span> <span class="p">(</span><span class="nd">&#39;a</span> <span class="p">-&gt;</span> <span class="n">unit</span><span class="p">)</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span> <span class="n">t</span>
      <span class="kr">val</span> <span class="nv">prepend</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">t</span> <span class="n">*</span> <span class="p">(</span><span class="nd">&#39;b</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span><span class="p">)</span> <span class="p">-&gt;</span> <span class="nd">&#39;b</span> <span class="n">t</span>
      <span class="kr">val</span> <span class="nv">prepare</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">t</span> <span class="n">*</span> <span class="nd">&#39;a</span> <span class="p">-&gt;</span> <span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span>
      <span class="kr">val</span> <span class="nv">switch</span><span class="p">:</span> <span class="p">(</span><span class="nd">&#39;a</span> <span class="n">t</span> <span class="p">-&gt;</span> <span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span>
   <span class="kr">end</span>
</pre></div></div></div>
<div class="paragraph"><p><span class="monospaced">MLton.Thread</span> provides access to MLton&#8217;s user-level thread
implementation (i.e. not OS-level threads).  Threads are lightweight
data structures that represent a paused computation.  Runnable threads
are threads that will begin or continue computing when <span class="monospaced">switch</span>-ed to.
<span class="monospaced">MLton.Thread</span> does not include a default scheduling mechanism, but it
can be used to implement both preemptive and non-preemptive threads.</p></div>
<div class="ulist"><ul>
<li>
<p>
<span class="monospaced">type AtomicState.t</span>
</p>
<div class="paragraph"><p>the type of atomic states.</p></div>
</li>
<li>
<p>
<span class="monospaced">atomically f</span>
</p>
<div class="paragraph"><p>runs <span class="monospaced">f</span> in a critical section.</p></div>
</li>
<li>
<p>
<span class="monospaced">atomicBegin ()</span>
</p>
<div class="paragraph"><p>begins a critical section.</p></div>
</li>
<li>
<p>
<span class="monospaced">atomicEnd ()</span>
</p>
<div class="paragraph"><p>ends a critical section.</p></div>
</li>
<li>
<p>
<span class="monospaced">atomicState ()</span>
</p>
<div class="paragraph"><p>returns the current atomic state.</p></div>
</li>
<li>
<p>
<span class="monospaced">type Runnable.t</span>
</p>
<div class="paragraph"><p>the type of threads that can be resumed.</p></div>
</li>
<li>
<p>
<span class="monospaced">type 'a t</span>
</p>
<div class="paragraph"><p>the type of threads that expect a value of type <span class="monospaced">'a</span>.</p></div>
</li>
<li>
<p>
<span class="monospaced">atomicSwitch f</span>
</p>
<div class="paragraph"><p>like <span class="monospaced">switch</span>, but assumes an atomic calling context.  Upon
<span class="monospaced">switch</span>-ing back to the current thread, an implicit <span class="monospaced">atomicEnd</span> is
performed.</p></div>
</li>
<li>
<p>
<span class="monospaced">new f</span>
</p>
<div class="paragraph"><p>creates a new thread that, when run, applies <span class="monospaced">f</span> to the value given to
the thread.  <span class="monospaced">f</span> must terminate by `switch`ing to another thread or
exiting the process.</p></div>
</li>
<li>
<p>
<span class="monospaced">prepend (t, f)</span>
</p>
<div class="paragraph"><p>creates a new thread (destroying <span class="monospaced">t</span> in the process) that first
applies <span class="monospaced">f</span> to the value given to the thread and then continues with
<span class="monospaced">t</span>.  This is a constant time operation.</p></div>
</li>
<li>
<p>
<span class="monospaced">prepare (t, v)</span>
</p>
<div class="paragraph"><p>prepares a new runnable thread (destroying <span class="monospaced">t</span> in the process) that
will evaluate <span class="monospaced">t</span> on <span class="monospaced">v</span>.</p></div>
</li>
<li>
<p>
<span class="monospaced">switch f</span>
</p>
<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
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>
is guaranteed to run atomically.</p></div>
</li>
</ul></div>
</div>
</div>
<div class="sect1">
<h2 id="_example_of_non_preemptive_threads">Example of non-preemptive threads</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content"><div class="highlight"><pre><span></span><span class="kr">structure</span> <span class="nn">Queue</span><span class="p">:</span>
   <span class="kr">sig</span>
      <span class="kr">type</span> <span class="nd">&#39;a</span> <span class="kt">t</span>

      <span class="kr">val</span> <span class="nv">new</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span> <span class="n">t</span>
      <span class="kr">val</span> <span class="nv">enque</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">t</span> <span class="n">*</span> <span class="nd">&#39;a</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">deque</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">t</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span> <span class="n">option</span>
   <span class="kr">end</span> <span class="p">=</span>
   <span class="kr">struct</span>
      <span class="kr">datatype</span> <span class="nd">&#39;a</span> <span class="kt">t</span> <span class="p">=</span> <span class="nc">T</span> <span class="kr">of</span> <span class="p">{</span><span class="n">front</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">list</span> <span class="n">ref</span><span class="p">,</span> <span class="n">back</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">list</span> <span class="n">ref</span><span class="p">}</span>

      <span class="kr">fun</span> <span class="nf">new</span> <span class="p">()</span> <span class="p">=</span> <span class="n">T</span> <span class="p">{</span><span class="n">front</span> <span class="p">=</span> <span class="n">ref</span> <span class="p">[],</span> <span class="n">back</span> <span class="p">=</span> <span class="n">ref</span> <span class="p">[]}</span>

      <span class="kr">fun</span> <span class="nf">enque</span> <span class="p">(</span><span class="n">T</span> <span class="p">{</span><span class="n">back</span><span class="p">,</span> <span class="p">...},</span> <span class="n">x</span><span class="p">)</span> <span class="p">=</span> <span class="n">back</span> <span class="n">:=</span> <span class="n">x</span> <span class="n">::</span> <span class="n">!back</span>

      <span class="kr">fun</span> <span class="nf">deque</span> <span class="p">(</span><span class="n">T</span> <span class="p">{</span><span class="n">front</span><span class="p">,</span> <span class="n">back</span><span class="p">})</span> <span class="p">=</span>
         <span class="kr">case</span> <span class="n">!front</span> <span class="kr">of</span>
            <span class="p">[]</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="kr">case</span> <span class="n">!back</span> <span class="kr">of</span>
                      <span class="p">[]</span> <span class="p">=&gt;</span> <span class="n">NONE</span>
                    <span class="n">|</span> <span class="n">l</span> <span class="p">=&gt;</span> <span class="kr">let</span> <span class="kr">val</span> <span class="nv">l</span> <span class="p">=</span> <span class="n">rev</span> <span class="n">l</span>
                           <span class="kr">in</span> <span class="kr">case</span> <span class="n">l</span> <span class="kr">of</span>
                              <span class="p">[]</span> <span class="p">=&gt;</span> <span class="kr">raise</span> <span class="n">Fail</span> <span class="s2">&quot;deque&quot;</span>
                            <span class="n">|</span> <span class="n">x</span> <span class="n">::</span> <span class="n">l</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="n">back</span> <span class="n">:=</span> <span class="p">[];</span> <span class="n">front</span> <span class="n">:=</span> <span class="n">l</span><span class="p">;</span> <span class="n">SOME</span> <span class="n">x</span><span class="p">)</span>
                           <span class="kr">end</span><span class="p">)</span>
          <span class="n">|</span> <span class="n">x</span> <span class="n">::</span> <span class="n">l</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="n">front</span> <span class="n">:=</span> <span class="n">l</span><span class="p">;</span> <span class="n">SOME</span> <span class="n">x</span><span class="p">)</span>
   <span class="kr">end</span>

<span class="kr">structure</span> <span class="nn">Thread</span><span class="p">:</span>
   <span class="kr">sig</span>
      <span class="kr">val</span> <span class="nv">exit</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span>
      <span class="kr">val</span> <span class="nv">run</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">spawn</span><span class="p">:</span> <span class="p">(</span><span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span><span class="p">)</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">yield</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span>
   <span class="kr">end</span> <span class="p">=</span>
   <span class="kr">struct</span>
      <span class="kr">open</span> <span class="nn">MLton</span>
      <span class="kr">open</span> <span class="nn">Thread</span>

      <span class="kr">val</span> <span class="nv">topLevel</span><span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="n">option</span> <span class="n">ref</span> <span class="p">=</span> <span class="n">ref</span> <span class="n">NONE</span>

      <span class="kr">local</span>
         <span class="kr">val</span> <span class="nv">threads</span><span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="nn">Queue</span><span class="p">.</span><span class="n">t</span> <span class="p">=</span> <span class="nn">Queue</span><span class="p">.</span><span class="n">new</span> <span class="p">()</span>
      <span class="kr">in</span>
         <span class="kr">fun</span> <span class="nf">ready</span> <span class="p">(</span><span class="n">t</span><span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span> <span class="p">:</span> <span class="n">unit</span> <span class="p">=</span>
            <span class="nn">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="n">t</span><span class="p">)</span>
         <span class="kr">fun</span> <span class="nf">next</span> <span class="p">()</span> <span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="p">=</span>
            <span class="kr">case</span> <span class="nn">Queue</span><span class="p">.</span><span class="n">deque</span> <span class="n">threads</span> <span class="kr">of</span>
               <span class="n">NONE</span> <span class="p">=&gt;</span> <span class="n">valOf</span> <span class="p">(</span><span class="n">!topLevel</span><span class="p">)</span>
             <span class="n">|</span> <span class="n">SOME</span> <span class="n">t</span> <span class="p">=&gt;</span> <span class="n">t</span>
      <span class="kr">end</span>

      <span class="kr">fun</span> <span class="nd">&#39;a</span> <span class="nf">exit</span> <span class="p">():</span> <span class="nd">&#39;a</span> <span class="p">=</span> <span class="n">switch</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">_</span> <span class="p">=&gt;</span> <span class="n">next</span> <span class="p">())</span>

      <span class="kr">fun</span> <span class="nf">new</span> <span class="p">(</span><span class="n">f</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span><span class="p">):</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="p">=</span>
         <span class="nn">Thread</span><span class="p">.</span><span class="n">prepare</span>
         <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">new</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">()</span> <span class="p">=&gt;</span> <span class="p">((</span><span class="n">f</span> <span class="p">()</span> <span class="kr">handle</span> <span class="p">_</span> <span class="p">=&gt;</span> <span class="n">exit</span> <span class="p">())</span>
                                <span class="p">;</span> <span class="n">exit</span> <span class="p">())),</span>
          <span class="p">())</span>

      <span class="kr">fun</span> <span class="nf">schedule</span> <span class="n">t</span> <span class="p">=</span> <span class="p">(</span><span class="n">ready</span> <span class="n">t</span><span class="p">;</span> <span class="n">next</span> <span class="p">())</span>

      <span class="kr">fun</span> <span class="nf">yield</span> <span class="p">():</span> <span class="n">unit</span> <span class="p">=</span> <span class="n">switch</span> <span class="p">(</span><span class="kr">fn</span> <span class="n">t</span> <span class="p">=&gt;</span> <span class="n">schedule</span> <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">prepare</span> <span class="p">(</span><span class="n">t</span><span class="p">,</span> <span class="p">())))</span>

      <span class="kr">val</span> <span class="nv">spawn</span> <span class="p">=</span> <span class="n">ready</span> <span class="n">o</span> <span class="n">new</span>

      <span class="kr">fun</span> <span class="nf">run</span><span class="p">():</span> <span class="n">unit</span> <span class="p">=</span>
         <span class="p">(</span><span class="n">switch</span> <span class="p">(</span><span class="kr">fn</span> <span class="n">t</span> <span class="p">=&gt;</span>
                  <span class="p">(</span><span class="n">topLevel</span> <span class="n">:=</span> <span class="n">SOME</span> <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">prepare</span> <span class="p">(</span><span class="n">t</span><span class="p">,</span> <span class="p">()))</span>
                   <span class="p">;</span> <span class="n">next</span><span class="p">()))</span>
          <span class="p">;</span> <span class="n">topLevel</span> <span class="n">:=</span> <span class="n">NONE</span><span class="p">)</span>
   <span class="kr">end</span>

<span class="kr">val</span> <span class="nv">rec</span> <span class="n">loop</span> <span class="p">=</span>
   <span class="kr">fn</span> <span class="mi">0</span> <span class="p">=&gt;</span> <span class="p">()</span>
    <span class="n">|</span> <span class="n">n</span> <span class="p">=&gt;</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="nn">Int</span><span class="p">.</span><span class="n">toString</span> <span class="n">n</span><span class="p">,</span> <span class="s2">&quot;</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">])</span>
            <span class="p">;</span> <span class="nn">Thread</span><span class="p">.</span><span class="n">yield</span><span class="p">()</span>
            <span class="p">;</span> <span class="n">loop</span><span class="p">(</span><span class="n">n</span> <span class="n">-</span> <span class="mi">1</span><span class="p">))</span>

<span class="kr">val</span> <span class="nv">rec</span> <span class="n">loop&#39;</span> <span class="p">=</span>
   <span class="kr">fn</span> <span class="mi">0</span> <span class="p">=&gt;</span> <span class="p">()</span>
    <span class="n">|</span> <span class="n">n</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">spawn</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">()</span> <span class="p">=&gt;</span> <span class="n">loop</span> <span class="n">n</span><span class="p">);</span> <span class="n">loop&#39;</span> <span class="p">(</span><span class="n">n</span> <span class="n">-</span> <span class="mi">2</span><span class="p">))</span>

<span class="kr">val</span> <span class="p">_</span> <span class="p">=</span> <span class="nn">Thread</span><span class="p">.</span><span class="n">spawn</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">()</span> <span class="p">=&gt;</span> <span class="n">loop&#39;</span> <span class="mi">10</span><span class="p">)</span>

<span class="kr">val</span> <span class="p">_</span> <span class="p">=</span> <span class="nn">Thread</span><span class="p">.</span><span class="n">run</span> <span class="p">()</span>

<span class="kr">val</span> <span class="p">_</span> <span class="p">=</span> <span class="n">print</span> <span class="s2">&quot;success</span><span class="se">\n</span><span class="s2">&quot;</span>
</pre></div></div></div>
</div>
</div>
<div class="sect1">
<h2 id="_example_of_preemptive_threads">Example of preemptive threads</h2>
<div class="sectionbody">
<div class="listingblock">
<div class="content"><div class="highlight"><pre><span></span><span class="kr">structure</span> <span class="nn">Queue</span><span class="p">:</span>
   <span class="kr">sig</span>
      <span class="kr">type</span> <span class="nd">&#39;a</span> <span class="kt">t</span>

      <span class="kr">val</span> <span class="nv">new</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span> <span class="n">t</span>
      <span class="kr">val</span> <span class="nv">enque</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">t</span> <span class="n">*</span> <span class="nd">&#39;a</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">deque</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">t</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span> <span class="n">option</span>
   <span class="kr">end</span> <span class="p">=</span>
   <span class="kr">struct</span>
      <span class="kr">datatype</span> <span class="nd">&#39;a</span> <span class="kt">t</span> <span class="p">=</span> <span class="nc">T</span> <span class="kr">of</span> <span class="p">{</span><span class="n">front</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">list</span> <span class="n">ref</span><span class="p">,</span> <span class="n">back</span><span class="p">:</span> <span class="nd">&#39;a</span> <span class="n">list</span> <span class="n">ref</span><span class="p">}</span>

      <span class="kr">fun</span> <span class="nf">new</span> <span class="p">()</span> <span class="p">=</span> <span class="n">T</span> <span class="p">{</span><span class="n">front</span> <span class="p">=</span> <span class="n">ref</span> <span class="p">[],</span> <span class="n">back</span> <span class="p">=</span> <span class="n">ref</span> <span class="p">[]}</span>

      <span class="kr">fun</span> <span class="nf">enque</span> <span class="p">(</span><span class="n">T</span> <span class="p">{</span><span class="n">back</span><span class="p">,</span> <span class="p">...},</span> <span class="n">x</span><span class="p">)</span> <span class="p">=</span> <span class="n">back</span> <span class="n">:=</span> <span class="n">x</span> <span class="n">::</span> <span class="n">!back</span>

      <span class="kr">fun</span> <span class="nf">deque</span> <span class="p">(</span><span class="n">T</span> <span class="p">{</span><span class="n">front</span><span class="p">,</span> <span class="n">back</span><span class="p">})</span> <span class="p">=</span>
         <span class="kr">case</span> <span class="n">!front</span> <span class="kr">of</span>
            <span class="p">[]</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="kr">case</span> <span class="n">!back</span> <span class="kr">of</span>
                      <span class="p">[]</span> <span class="p">=&gt;</span> <span class="n">NONE</span>
                    <span class="n">|</span> <span class="n">l</span> <span class="p">=&gt;</span> <span class="kr">let</span> <span class="kr">val</span> <span class="nv">l</span> <span class="p">=</span> <span class="n">rev</span> <span class="n">l</span>
                           <span class="kr">in</span> <span class="kr">case</span> <span class="n">l</span> <span class="kr">of</span>
                              <span class="p">[]</span> <span class="p">=&gt;</span> <span class="kr">raise</span> <span class="n">Fail</span> <span class="s2">&quot;deque&quot;</span>
                            <span class="n">|</span> <span class="n">x</span> <span class="n">::</span> <span class="n">l</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="n">back</span> <span class="n">:=</span> <span class="p">[];</span> <span class="n">front</span> <span class="n">:=</span> <span class="n">l</span><span class="p">;</span> <span class="n">SOME</span> <span class="n">x</span><span class="p">)</span>
                           <span class="kr">end</span><span class="p">)</span>
          <span class="n">|</span> <span class="n">x</span> <span class="n">::</span> <span class="n">l</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="n">front</span> <span class="n">:=</span> <span class="n">l</span><span class="p">;</span> <span class="n">SOME</span> <span class="n">x</span><span class="p">)</span>
   <span class="kr">end</span>

<span class="kr">structure</span> <span class="nn">Thread</span><span class="p">:</span>
   <span class="kr">sig</span>
      <span class="kr">val</span> <span class="nv">exit</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="nd">&#39;a</span>
      <span class="kr">val</span> <span class="nv">run</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">spawn</span><span class="p">:</span> <span class="p">(</span><span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span><span class="p">)</span> <span class="p">-&gt;</span> <span class="n">unit</span>
      <span class="kr">val</span> <span class="nv">yield</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span>
   <span class="kr">end</span> <span class="p">=</span>
   <span class="kr">struct</span>
      <span class="kr">open</span> <span class="nn">Posix</span><span class="err">.Signal</span>
      <span class="kr">open</span> <span class="nn">MLton</span>
      <span class="kr">open</span> <span class="nn">Itimer</span> <span class="nn">Signal</span> <span class="nn">Thread</span>

      <span class="kr">val</span> <span class="nv">topLevel</span><span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="n">option</span> <span class="n">ref</span> <span class="p">=</span> <span class="n">ref</span> <span class="n">NONE</span>

      <span class="kr">local</span>
         <span class="kr">val</span> <span class="nv">threads</span><span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="nn">Queue</span><span class="p">.</span><span class="n">t</span> <span class="p">=</span> <span class="nn">Queue</span><span class="p">.</span><span class="n">new</span> <span class="p">()</span>
      <span class="kr">in</span>
         <span class="kr">fun</span> <span class="nf">ready</span> <span class="p">(</span><span class="n">t</span><span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span><span class="p">)</span> <span class="p">:</span> <span class="n">unit</span> <span class="p">=</span>
            <span class="nn">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="n">t</span><span class="p">)</span>
         <span class="kr">fun</span> <span class="nf">next</span> <span class="p">()</span> <span class="p">:</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="p">=</span>
            <span class="kr">case</span> <span class="nn">Queue</span><span class="p">.</span><span class="n">deque</span> <span class="n">threads</span> <span class="kr">of</span>
               <span class="n">NONE</span> <span class="p">=&gt;</span> <span class="n">valOf</span> <span class="p">(</span><span class="n">!topLevel</span><span class="p">)</span>
             <span class="n">|</span> <span class="n">SOME</span> <span class="n">t</span> <span class="p">=&gt;</span> <span class="n">t</span>
      <span class="kr">end</span>

      <span class="kr">fun</span> <span class="nd">&#39;a</span> <span class="nf">exit</span> <span class="p">():</span> <span class="nd">&#39;a</span> <span class="p">=</span> <span class="n">switch</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">_</span> <span class="p">=&gt;</span> <span class="n">next</span> <span class="p">())</span>

      <span class="kr">fun</span> <span class="nf">new</span> <span class="p">(</span><span class="n">f</span><span class="p">:</span> <span class="n">unit</span> <span class="p">-&gt;</span> <span class="n">unit</span><span class="p">):</span> <span class="nn">Thread</span><span class="p">.</span><span class="nn">Runnable</span><span class="p">.</span><span class="n">t</span> <span class="p">=</span>
         <span class="nn">Thread</span><span class="p">.</span><span class="n">prepare</span>
         <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">new</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">()</span> <span class="p">=&gt;</span> <span class="p">((</span><span class="n">f</span> <span class="p">()</span> <span class="kr">handle</span> <span class="p">_</span> <span class="p">=&gt;</span> <span class="n">exit</span> <span class="p">())</span>
                                <span class="p">;</span> <span class="n">exit</span> <span class="p">())),</span>
          <span class="p">())</span>

      <span class="kr">fun</span> <span class="nf">schedule</span> <span class="n">t</span> <span class="p">=</span> <span class="p">(</span><span class="n">ready</span> <span class="n">t</span><span class="p">;</span> <span class="n">next</span> <span class="p">())</span>

      <span class="kr">fun</span> <span class="nf">yield</span> <span class="p">():</span> <span class="n">unit</span> <span class="p">=</span> <span class="n">switch</span> <span class="p">(</span><span class="kr">fn</span> <span class="n">t</span> <span class="p">=&gt;</span> <span class="n">schedule</span> <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">prepare</span> <span class="p">(</span><span class="n">t</span><span class="p">,</span> <span class="p">())))</span>

      <span class="kr">val</span> <span class="nv">spawn</span> <span class="p">=</span> <span class="n">ready</span> <span class="n">o</span> <span class="n">new</span>

      <span class="kr">fun</span> <span class="nf">setItimer</span> <span class="n">t</span> <span class="p">=</span>
         <span class="nn">Itimer</span><span class="p">.</span><span class="n">set</span> <span class="p">(</span><span class="nn">Itimer</span><span class="p">.</span><span class="n">Real</span><span class="p">,</span>
                     <span class="p">{</span><span class="n">value</span> <span class="p">=</span> <span class="n">t</span><span class="p">,</span>
                      <span class="n">interval</span> <span class="p">=</span> <span class="n">t</span><span class="p">})</span>

      <span class="kr">fun</span> <span class="nf">run</span> <span class="p">():</span> <span class="n">unit</span> <span class="p">=</span>
         <span class="p">(</span><span class="n">switch</span> <span class="p">(</span><span class="kr">fn</span> <span class="n">t</span> <span class="p">=&gt;</span>
                  <span class="p">(</span><span class="n">topLevel</span> <span class="n">:=</span> <span class="n">SOME</span> <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">prepare</span> <span class="p">(</span><span class="n">t</span><span class="p">,</span> <span class="p">()))</span>
                   <span class="p">;</span> <span class="n">new</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">()</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="n">setHandler</span> <span class="p">(</span><span class="n">alrm</span><span class="p">,</span> <span class="nn">Handler</span><span class="p">.</span><span class="n">handler</span> <span class="n">schedule</span><span class="p">)</span>
                                    <span class="p">;</span> <span class="n">setItimer</span> <span class="p">(</span><span class="nn">Time</span><span class="p">.</span><span class="n">fromMilliseconds</span> <span class="mi">20</span><span class="p">)))))</span>
          <span class="p">;</span> <span class="n">setItimer</span> <span class="nn">Time</span><span class="p">.</span><span class="n">zeroTime</span>
          <span class="p">;</span> <span class="n">ignore</span> <span class="n">alrm</span>
          <span class="p">;</span> <span class="n">topLevel</span> <span class="n">:=</span> <span class="n">NONE</span><span class="p">)</span>
   <span class="kr">end</span>

<span class="kr">val</span> <span class="nv">rec</span> <span class="n">delay</span> <span class="p">=</span>
   <span class="kr">fn</span> <span class="mi">0</span> <span class="p">=&gt;</span> <span class="p">()</span>
    <span class="n">|</span> <span class="n">n</span> <span class="p">=&gt;</span> <span class="n">delay</span> <span class="p">(</span><span class="n">n</span> <span class="n">-</span> <span class="mi">1</span><span class="p">)</span>

<span class="kr">val</span> <span class="nv">rec</span> <span class="n">loop</span> <span class="p">=</span>
   <span class="kr">fn</span> <span class="mi">0</span> <span class="p">=&gt;</span> <span class="p">()</span>
    <span class="n">|</span> <span class="n">n</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="n">delay</span> <span class="mi">500000</span><span class="p">;</span> <span class="n">loop</span> <span class="p">(</span><span class="n">n</span> <span class="n">-</span> <span class="mi">1</span><span class="p">))</span>

<span class="kr">val</span> <span class="nv">rec</span> <span class="n">loop&#39;</span> <span class="p">=</span>
   <span class="kr">fn</span> <span class="mi">0</span> <span class="p">=&gt;</span> <span class="p">()</span>
    <span class="n">|</span> <span class="n">n</span> <span class="p">=&gt;</span> <span class="p">(</span><span class="nn">Thread</span><span class="p">.</span><span class="n">spawn</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">()</span> <span class="p">=&gt;</span> <span class="n">loop</span> <span class="n">n</span><span class="p">);</span> <span class="n">loop&#39;</span> <span class="p">(</span><span class="n">n</span> <span class="n">-</span> <span class="mi">1</span><span class="p">))</span>

<span class="kr">val</span> <span class="p">_</span> <span class="p">=</span> <span class="nn">Thread</span><span class="p">.</span><span class="n">spawn</span> <span class="p">(</span><span class="kr">fn</span> <span class="p">()</span> <span class="p">=&gt;</span> <span class="n">loop&#39;</span> <span class="mi">10</span><span class="p">)</span>

<span class="kr">val</span> <span class="p">_</span> <span class="p">=</span> <span class="nn">Thread</span><span class="p">.</span><span class="n">run</span> <span class="p">()</span>

<span class="kr">val</span> <span class="p">_</span> <span class="p">=</span> <span class="n">print</span> <span class="s2">&quot;success</span><span class="se">\n</span><span class="s2">&quot;</span>
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