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<span class="Comment">//: Routines can be put in a 'waiting' state, from which it will be ready to</span>
<span class="Comment">//: run again when a specific memory location changes its value. This is mu's</span>
<span class="Comment">//: basic technique for orchestrating the order in which different routines</span>
<span class="Comment">//: operate.</span>

<span class="Delimiter">:(scenario wait_for_location)</span>
recipe f1 [
  <span class="Constant">1</span>:number<span class="Special"> &lt;- </span>copy <span class="Constant">0</span>:literal
  start-running f2:recipe
  wait-for-location <span class="Constant">1</span>:number
  <span class="Comment"># now wait for f2 to run and modify location 1 before using its value</span>
  <span class="Constant">2</span>:number<span class="Special"> &lt;- </span>copy <span class="Constant">1</span>:number
]
recipe f2 [
  <span class="Constant">1</span>:number<span class="Special"> &lt;- </span>copy <span class="Constant">34</span>:literal
]
<span class="Comment"># if we got the synchronization wrong we'd be storing 0 in location 2</span>
<span class="traceContains">+mem: storing 34 in location 2</span>

<span class="Comment">//: define the new state that all routines can be in</span>

<span class="Delimiter">:(before &quot;End routine States&quot;)</span>
WAITING<span class="Delimiter">,</span>
<span class="Delimiter">:(before &quot;End routine Fields&quot;)</span>
<span class="Comment">// only if state == WAITING</span>
long long int waiting_on_location<span class="Delimiter">;</span>
int old_value_of_waiting_location<span class="Delimiter">;</span>
<span class="Delimiter">:(before &quot;End routine Constructor&quot;)</span>
waiting_on_location = old_value_of_waiting_location = <span class="Constant">0</span><span class="Delimiter">;</span>

<span class="Comment">//: primitive recipe to put routines in that state</span>

<span class="Delimiter">:(before &quot;End Primitive Recipe Declarations&quot;)</span>
WAIT_FOR_LOCATION<span class="Delimiter">,</span>
<span class="Delimiter">:(before &quot;End Primitive Recipe Numbers&quot;)</span>
Recipe_ordinal[<span class="Constant">&quot;wait-for-location&quot;</span>] = WAIT_FOR_LOCATION<span class="Delimiter">;</span>
<span class="Delimiter">:(before &quot;End Primitive Recipe Implementations&quot;)</span>
case WAIT_FOR_LOCATION: <span class="Delimiter">{</span>
  reagent loc = canonize<span class="Delimiter">(</span>current_instruction<span class="Delimiter">().</span>ingredients<span class="Delimiter">.</span>at<span class="Delimiter">(</span><span class="Constant">0</span><span class="Delimiter">));</span>
  Current_routine<span class="Delimiter">-&gt;</span>state = WAITING<span class="Delimiter">;</span>
  Current_routine<span class="Delimiter">-&gt;</span>waiting_on_location = loc<span class="Delimiter">.</span>value<span class="Delimiter">;</span>
  Current_routine<span class="Delimiter">-&gt;</span>old_value_of_waiting_location = Memory[loc<span class="Delimiter">.</span>value]<span class="Delimiter">;</span>
  trace<span class="Delimiter">(</span>Primitive_recipe_depth<span class="Delimiter">,</span> <span class="Constant">&quot;run&quot;</span><span class="Delimiter">)</span> &lt;&lt; <span class="Constant">&quot;waiting for location &quot;</span> &lt;&lt; loc<span class="Delimiter">.</span>value &lt;&lt; <span class="Constant">&quot; to change from &quot;</span> &lt;&lt; Memory[loc<span class="Delimiter">.</span>value]<span class="Delimiter">;</span>
<span class="CommentedCode">//?   trace(&quot;schedule&quot;) &lt;&lt; Current_routine-&gt;id &lt;&lt; &quot;: waiting for location &quot; &lt;&lt; loc.value &lt;&lt; &quot; to change from &quot; &lt;&lt; Memory[loc.value]; //? 2</span>
  <span class="Identifier">break</span><span class="Delimiter">;</span>
<span class="Delimiter">}</span>

<span class="Comment">//: scheduler tweak to get routines out of that state</span>

<span class="Delimiter">:(before &quot;End Scheduler State Transitions&quot;)</span>
for <span class="Delimiter">(</span>long long int i = <span class="Constant">0</span><span class="Delimiter">;</span> i &lt; SIZE<span class="Delimiter">(</span>Routines<span class="Delimiter">);</span> ++i<span class="Delimiter">)</span> <span class="Delimiter">{</span>
<span class="CommentedCode">//?   trace(&quot;schedule&quot;) &lt;&lt; &quot;wake up loop 1: routine &quot; &lt;&lt; Routines.at(i)-&gt;id &lt;&lt; &quot; has state &quot; &lt;&lt; Routines.at(i)-&gt;state; //? 1</span>
  if <span class="Delimiter">(</span>Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>state != WAITING<span class="Delimiter">)</span> <span class="Identifier">continue</span><span class="Delimiter">;</span>
<span class="CommentedCode">//?   trace(&quot;schedule&quot;) &lt;&lt; &quot;waiting on location: &quot; &lt;&lt; Routines.at(i)-&gt;waiting_on_location; //? 1</span>
<span class="CommentedCode">//?   if (Routines.at(i)-&gt;waiting_on_location) //? 2</span>
<span class="CommentedCode">//?     trace(&quot;schedule&quot;) &lt;&lt; &quot;checking routine &quot; &lt;&lt; Routines.at(i)-&gt;id &lt;&lt; &quot; waiting on location &quot; //? 2</span>
<span class="CommentedCode">//?       &lt;&lt; Routines.at(i)-&gt;waiting_on_location &lt;&lt; &quot;: &quot; &lt;&lt; Memory[Routines.at(i)-&gt;waiting_on_location] &lt;&lt; &quot; vs &quot; &lt;&lt; Routines.at(i)-&gt;old_value_of_waiting_location; //? 2</span>
  if <span class="Delimiter">(</span>Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>waiting_on_location &amp;&amp;
      Memory[Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>waiting_on_location] != Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>old_value_of_waiting_location<span class="Delimiter">)</span> <span class="Delimiter">{</span>
    trace<span class="Delimiter">(</span><span class="Constant">&quot;schedule&quot;</span><span class="Delimiter">)</span> &lt;&lt; <span class="Constant">&quot;waking up routine</span><span class="cSpecial">\n</span><span class="Constant">&quot;</span><span class="Delimiter">;</span>
    Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>state = RUNNING<span class="Delimiter">;</span>
    Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>waiting_on_location = Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>old_value_of_waiting_location = <span class="Constant">0</span><span class="Delimiter">;</span>
  <span class="Delimiter">}</span>
<span class="Delimiter">}</span>

<span class="Comment">//: also allow waiting on a routine to stop running</span>

<span class="Delimiter">:(scenario wait_for_routine)</span>
recipe f1 [
  <span class="Constant">1</span>:number<span class="Special"> &lt;- </span>copy <span class="Constant">0</span>:literal
  <span class="Constant">12</span>:number/routine<span class="Special"> &lt;- </span>start-running f2:recipe
  wait-for-routine <span class="Constant">12</span>:number/routine
  <span class="Comment"># now wait for f2 to run and modify location 1 before using its value</span>
  <span class="Constant">3</span>:number<span class="Special"> &lt;- </span>copy <span class="Constant">1</span>:number
]
recipe f2 [
  <span class="Constant">1</span>:number<span class="Special"> &lt;- </span>copy <span class="Constant">34</span>:literal
]
<span class="traceContains">+schedule: f1</span>
<span class="traceContains">+run: waiting for routine 2</span>
<span class="traceContains">+schedule: f2</span>
<span class="traceContains">+schedule: waking up routine 1</span>
<span class="traceContains">+schedule: f1</span>
<span class="Comment"># if we got the synchronization wrong we'd be storing 0 in location 3</span>
<span class="traceContains">+mem: storing 34 in location 3</span>

<span class="Delimiter">:(before &quot;End routine Fields&quot;)</span>
<span class="Comment">// only if state == WAITING</span>
long long int waiting_on_routine<span class="Delimiter">;</span>
<span class="Delimiter">:(before &quot;End routine Constructor&quot;)</span>
waiting_on_routine = <span class="Constant">0</span><span class="Delimiter">;</span>

<span class="Delimiter">:(before &quot;End Primitive Recipe Declarations&quot;)</span>
WAIT_FOR_ROUTINE<span class="Delimiter">,</span>
<span class="Delimiter">:(before &quot;End Primitive Recipe Numbers&quot;)</span>
Recipe_ordinal[<span class="Constant">&quot;wait-for-routine&quot;</span>] = WAIT_FOR_ROUTINE<span class="Delimiter">;</span>
<span class="Delimiter">:(before &quot;End Primitive Recipe Implementations&quot;)</span>
case WAIT_FOR_ROUTINE: <span class="Delimiter">{</span>
  Current_routine<span class="Delimiter">-&gt;</span>state = WAITING<span class="Delimiter">;</span>
  assert<span class="Delimiter">(</span>scalar<span class="Delimiter">(</span>ingredients<span class="Delimiter">.</span>at<span class="Delimiter">(</span><span class="Constant">0</span><span class="Delimiter">)));</span>
  Current_routine<span class="Delimiter">-&gt;</span>waiting_on_routine = ingredients<span class="Delimiter">.</span>at<span class="Delimiter">(</span><span class="Constant">0</span><span class="Delimiter">).</span>at<span class="Delimiter">(</span><span class="Constant">0</span><span class="Delimiter">);</span>
  trace<span class="Delimiter">(</span>Primitive_recipe_depth<span class="Delimiter">,</span> <span class="Constant">&quot;run&quot;</span><span class="Delimiter">)</span> &lt;&lt; <span class="Constant">&quot;waiting for routine &quot;</span> &lt;&lt; ingredients<span class="Delimiter">.</span>at<span class="Delimiter">(</span><span class="Constant">0</span><span class="Delimiter">).</span>at<span class="Delimiter">(</span><span class="Constant">0</span><span class="Delimiter">);</span>
  <span class="Identifier">break</span><span class="Delimiter">;</span>
<span class="Delimiter">}</span>

<span class="Delimiter">:(before &quot;End Scheduler State Transitions&quot;)</span>
<span class="Comment">// Wake up any routines waiting for other routines to go to sleep.</span>
<span class="Comment">// Important: this must come after the scheduler loop above giving routines</span>
<span class="Comment">// waiting for locations to change a chance to wake up.</span>
for <span class="Delimiter">(</span>long long int i = <span class="Constant">0</span><span class="Delimiter">;</span> i &lt; SIZE<span class="Delimiter">(</span>Routines<span class="Delimiter">);</span> ++i<span class="Delimiter">)</span> <span class="Delimiter">{</span>
  if <span class="Delimiter">(</span>Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>state != WAITING<span class="Delimiter">)</span> <span class="Identifier">continue</span><span class="Delimiter">;</span>
  if <span class="Delimiter">(</span>!Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>waiting_on_routine<span class="Delimiter">)</span> <span class="Identifier">continue</span><span class="Delimiter">;</span>
  long long int id = Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>waiting_on_routine<span class="Delimiter">;</span>
  assert<span class="Delimiter">(</span>id != Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>id<span class="Delimiter">);</span>
  for <span class="Delimiter">(</span>long long int j = <span class="Constant">0</span><span class="Delimiter">;</span> j &lt; SIZE<span class="Delimiter">(</span>Routines<span class="Delimiter">);</span> ++j<span class="Delimiter">)</span> <span class="Delimiter">{</span>
    if <span class="Delimiter">(</span>Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>j<span class="Delimiter">)-&gt;</span>id == id &amp;&amp; Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>j<span class="Delimiter">)-&gt;</span>state != RUNNING<span class="Delimiter">)</span> <span class="Delimiter">{</span>
      trace<span class="Delimiter">(</span><span class="Constant">&quot;schedule&quot;</span><span class="Delimiter">)</span> &lt;&lt; <span class="Constant">&quot;waking up routine &quot;</span> &lt;&lt; Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>id<span class="Delimiter">;</span>
      Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>state = RUNNING<span class="Delimiter">;</span>
      Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>waiting_on_routine = <span class="Constant">0</span><span class="Delimiter">;</span>
    <span class="Delimiter">}</span>
  <span class="Delimiter">}</span>
<span class="Delimiter">}</span>

<span class="Delimiter">:(before &quot;End Primitive Recipe Declarations&quot;)</span>
SWITCH<span class="Delimiter">,</span>
<span class="Delimiter">:(before &quot;End Primitive Recipe Numbers&quot;)</span>
Recipe_ordinal[<span class="Constant">&quot;switch&quot;</span>] = SWITCH<span class="Delimiter">;</span>
<span class="Delimiter">:(before &quot;End Primitive Recipe Implementations&quot;)</span>
case SWITCH: <span class="Delimiter">{</span>
  long long int id = some_other_running_routine<span class="Delimiter">();</span>
  if <span class="Delimiter">(</span>id<span class="Delimiter">)</span> <span class="Delimiter">{</span>
    assert<span class="Delimiter">(</span>id != Current_routine<span class="Delimiter">-&gt;</span>id<span class="Delimiter">);</span>
<span class="CommentedCode">//?     cerr &lt;&lt; &quot;waiting on &quot; &lt;&lt; id &lt;&lt; &quot; from &quot; &lt;&lt; Current_routine-&gt;id &lt;&lt; '\n'; //? 1</span>
    Current_routine<span class="Delimiter">-&gt;</span>state = WAITING<span class="Delimiter">;</span>
    Current_routine<span class="Delimiter">-&gt;</span>waiting_on_routine = id<span class="Delimiter">;</span>
  <span class="Delimiter">}</span>
  <span class="Identifier">break</span><span class="Delimiter">;</span>
<span class="Delimiter">}</span>

<span class="Delimiter">:(code)</span>
long long int some_other_running_routine<span class="Delimiter">()</span> <span class="Delimiter">{</span>
  for <span class="Delimiter">(</span>long long int i = <span class="Constant">0</span><span class="Delimiter">;</span> i &lt; SIZE<span class="Delimiter">(</span>Routines<span class="Delimiter">);</span> ++i<span class="Delimiter">)</span> <span class="Delimiter">{</span>
    if <span class="Delimiter">(</span>i == Current_routine_index<span class="Delimiter">)</span> <span class="Identifier">continue</span><span class="Delimiter">;</span>
    assert<span class="Delimiter">(</span>Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)</span> != Current_routine<span class="Delimiter">);</span>
    assert<span class="Delimiter">(</span>Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>id != Current_routine<span class="Delimiter">-&gt;</span>id<span class="Delimiter">);</span>
    if <span class="Delimiter">(</span>Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>state == RUNNING<span class="Delimiter">)</span>
      <span class="Identifier">return</span> Routines<span class="Delimiter">.</span>at<span class="Delimiter">(</span>i<span class="Delimiter">)-&gt;</span>id<span class="Delimiter">;</span>
  <span class="Delimiter">}</span>
  <span class="Identifier">return</span> <span class="Constant">0</span><span class="Delimiter">;</span>
<span class="Delimiter">}</span>
</pre>
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