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<pre id='vimCodeElement'>
<span class="Comment"># Mu synchronizes using channels rather than locks, like Erlang and Go.</span>
<span class="Comment">#</span>
<span class="Comment"># The two ends of a channel will usually belong to different routines, but</span>
<span class="Comment"># each end should only be used by a single one. Don't try to read from or</span>
<span class="Comment"># write to it from multiple routines at once.</span>
<span class="Comment">#</span>
<span class="Comment"># The key property of channels is that writing to a full channel or reading</span>
<span class="Comment"># from an empty one will put the current routine in 'waiting' state until the</span>
<span class="Comment"># operation can be completed.</span>

scenario channel [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">3:literal/capacity</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    2:number, 1:address:channel<span class="Special"> &lt;- </span>read 1:address:channel
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>34
  ]
]

container channel [
  <span class="Comment"># To avoid locking, writer and reader will never write to the same location.</span>
  <span class="Comment"># So channels will include fields in pairs, one for the writer and one for the</span>
  <span class="Comment"># reader.</span>
  first-full:number  <span class="Comment"># for write</span>
  first-free:number  <span class="Comment"># for read</span>
  <span class="Comment"># A circular buffer contains values from index first-full up to (but not</span>
  <span class="Comment"># including) index first-empty. The reader always modifies it at first-full,</span>
  <span class="Comment"># while the writer always modifies it at first-empty.</span>
  data:address:array:location
]

<span class="Comment"># result:address:channel &lt;- init-channel capacity:number</span>
recipe init-channel [
  default-space:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
  <span class="Comment"># result = new channel</span>
  result:address:channel<span class="Special"> &lt;- </span>new channel:type
  <span class="Comment"># result.first-full = 0</span>
  full:address:number<span class="Special"> &lt;- </span>get-address result:address:channel/deref, first-full:offset
  full:address:number/deref<span class="Special"> &lt;- </span>copy <span class="Constant">0:literal</span>
  <span class="Comment"># result.first-free = 0</span>
  free:address:number<span class="Special"> &lt;- </span>get-address result:address:channel/deref, first-free:offset
  free:address:number/deref<span class="Special"> &lt;- </span>copy <span class="Constant">0:literal</span>
  <span class="Comment"># result.data = new location[ingredient+1]</span>
  capacity:number<span class="Special"> &lt;- </span>next-ingredient
  capacity:number<span class="Special"> &lt;- </span>add capacity:number, <span class="Constant">1:literal</span>  <span class="Comment"># unused slot for 'full?' below</span>
  dest:address:address:array:location<span class="Special"> &lt;- </span>get-address result:address:channel/deref, data:offset
  dest:address:address:array:location/deref<span class="Special"> &lt;- </span>new location:type, capacity:number
  <span class="Identifier">reply</span> result:address:channel
]

<span class="Comment"># chan:address:channel &lt;- write chan:address:channel, val:location</span>
recipe write [
  default-space:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
  chan:address:channel<span class="Special"> &lt;- </span>next-ingredient
  val:location<span class="Special"> &lt;- </span>next-ingredient
  <span class="Delimiter">{</span>
    <span class="Comment"># block if chan is full</span>
    full:boolean<span class="Special"> &lt;- </span>channel-full? chan:address:channel
    <span class="Identifier">break-unless</span> full:boolean
    full-address:address:number<span class="Special"> &lt;- </span>get-address chan:address:channel/deref, first-full:offset
    wait-for-location full-address:address:number/deref
  <span class="Delimiter">}</span>
  <span class="Comment"># store val</span>
  circular-buffer:address:array:location<span class="Special"> &lt;- </span>get chan:address:channel/deref, data:offset
  free:address:number<span class="Special"> &lt;- </span>get-address chan:address:channel/deref, first-free:offset
  dest:address:location<span class="Special"> &lt;- </span>index-address circular-buffer:address:array:location/deref, free:address:number/deref
  dest:address:location/deref<span class="Special"> &lt;- </span>copy val:location
  <span class="Comment"># increment free</span>
  free:address:number/deref<span class="Special"> &lt;- </span>add free:address:number/deref, <span class="Constant">1:literal</span>
  <span class="Delimiter">{</span>
    <span class="Comment"># wrap free around to 0 if necessary</span>
    len:number<span class="Special"> &lt;- </span>length circular-buffer:address:array:location/deref
    at-end?:boolean<span class="Special"> &lt;- </span>greater-or-equal free:address:number/deref, len:number
    <span class="Identifier">break-unless</span> at-end?:boolean
    free:address:number/deref<span class="Special"> &lt;- </span>copy <span class="Constant">0:literal</span>
  <span class="Delimiter">}</span>
  <span class="Identifier">reply</span> chan:address:channel/same-as-ingredient:0
]

<span class="Comment"># result:location, chan:address:channel &lt;- read chan:address:channel</span>
recipe read [
  default-space:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
  chan:address:channel<span class="Special"> &lt;- </span>next-ingredient
  <span class="Delimiter">{</span>
    <span class="Comment"># block if chan is empty</span>
    empty:boolean<span class="Special"> &lt;- </span>channel-empty? chan:address:channel
    <span class="Identifier">break-unless</span> empty:boolean
    free-address:address:number<span class="Special"> &lt;- </span>get-address chan:address:channel/deref, first-free:offset
    wait-for-location free-address:address:number/deref
  <span class="Delimiter">}</span>
  <span class="Comment"># read result</span>
  full:address:number<span class="Special"> &lt;- </span>get-address chan:address:channel/deref, first-full:offset
  circular-buffer:address:array:location<span class="Special"> &lt;- </span>get chan:address:channel/deref, data:offset
  result:location<span class="Special"> &lt;- </span>index circular-buffer:address:array:location/deref, full:address:number/deref
  <span class="Comment"># increment full</span>
  full:address:number/deref<span class="Special"> &lt;- </span>add full:address:number/deref, <span class="Constant">1:literal</span>
  <span class="Delimiter">{</span>
    <span class="Comment"># wrap full around to 0 if necessary</span>
    len:number<span class="Special"> &lt;- </span>length circular-buffer:address:array:location/deref
    at-end?:boolean<span class="Special"> &lt;- </span>greater-or-equal full:address:number/deref, len:number
    <span class="Identifier">break-unless</span> at-end?:boolean
    full:address:number/deref<span class="Special"> &lt;- </span>copy <span class="Constant">0:literal</span>
  <span class="Delimiter">}</span>
  <span class="Identifier">reply</span> result:location, chan:address:channel/same-as-ingredient:0
]

recipe clear-channel [
  default-space:address:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
  chan:address:channel<span class="Special"> &lt;- </span>next-ingredient
  <span class="Delimiter">{</span>
    empty?:boolean<span class="Special"> &lt;- </span>channel-empty? chan:address:channel
    <span class="Identifier">break-if</span> empty?:boolean
    _, chan:address:channel<span class="Special"> &lt;- </span>read chan:address:channel
  <span class="Delimiter">}</span>
  <span class="Identifier">reply</span> chan:address:channel/same-as-ingredient:0
]

scenario channel-initialization [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">3:literal/capacity</span>
    2:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-full:offset
    3:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-free:offset
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>0  <span class="Comment"># first-full</span>
    3<span class="Special"> &lt;- </span>0  <span class="Comment"># first-free</span>
  ]
]

scenario channel-write-increments-free [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">3:literal/capacity</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    2:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-full:offset
    3:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-free:offset
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>0  <span class="Comment"># first-full</span>
    3<span class="Special"> &lt;- </span>1  <span class="Comment"># first-free</span>
  ]
]

scenario channel-read-increments-full [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">3:literal/capacity</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    _, 1:address:channel<span class="Special"> &lt;- </span>read 1:address:channel
    2:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-full:offset
    3:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-free:offset
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>1  <span class="Comment"># first-full</span>
    3<span class="Special"> &lt;- </span>1  <span class="Comment"># first-free</span>
  ]
]

scenario channel-wrap [
  run [
    <span class="Comment"># channel with just 1 slot</span>
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">1:literal/capacity</span>
    <span class="Comment"># write and read a value</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    _, 1:address:channel<span class="Special"> &lt;- </span>read 1:address:channel
    <span class="Comment"># first-free will now be 1</span>
    2:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-free:offset
    3:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-free:offset
    <span class="Comment"># write second value, verify that first-free wraps</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    4:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-free:offset
    <span class="Comment"># read second value, verify that first-full wraps</span>
    _, 1:address:channel<span class="Special"> &lt;- </span>read 1:address:channel
    5:number<span class="Special"> &lt;- </span>get 1:address:channel/deref, first-full:offset
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>1  <span class="Comment"># first-free after first write</span>
    3<span class="Special"> &lt;- </span>1  <span class="Comment"># first-full after first read</span>
    4<span class="Special"> &lt;- </span>0  <span class="Comment"># first-free after second write, wrapped</span>
    5<span class="Special"> &lt;- </span>0  <span class="Comment"># first-full after second read, wrapped</span>
  ]
]

<span class="SalientComment">## helpers</span>

<span class="Comment"># An empty channel has first-empty and first-full both at the same value.</span>
recipe channel-empty? [
  default-space:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
  chan:address:channel<span class="Special"> &lt;- </span>next-ingredient
  <span class="Comment"># return chan.first-full == chan.first-free</span>
  full:number<span class="Special"> &lt;- </span>get chan:address:channel/deref, first-full:offset
  free:number<span class="Special"> &lt;- </span>get chan:address:channel/deref, first-free:offset
  result:boolean<span class="Special"> &lt;- </span>equal full:number, free:number
  <span class="Identifier">reply</span> result:boolean
]

<span class="Comment"># A full channel has first-empty just before first-full, wasting one slot.</span>
<span class="Comment"># (Other alternatives: <a href="https://en.wikipedia.org/wiki/Circular_buffer#Full_.2F_Empty_Buffer_Distinction)">https://en.wikipedia.org/wiki/Circular_buffer#Full_.2F_Empty_Buffer_Distinction)</a></span>
recipe channel-full? [
  default-space:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
  chan:address:channel<span class="Special"> &lt;- </span>next-ingredient
  <span class="Comment"># tmp = chan.first-free + 1</span>
  tmp:number<span class="Special"> &lt;- </span>get chan:address:channel/deref, first-free:offset
  tmp:number<span class="Special"> &lt;- </span>add tmp:number, <span class="Constant">1:literal</span>
  <span class="Delimiter">{</span>
    <span class="Comment"># if tmp == chan.capacity, tmp = 0</span>
    len:number<span class="Special"> &lt;- </span>channel-capacity chan:address:channel
    at-end?:boolean<span class="Special"> &lt;- </span>greater-or-equal tmp:number, len:number
    <span class="Identifier">break-unless</span> at-end?:boolean
    tmp:number<span class="Special"> &lt;- </span>copy <span class="Constant">0:literal</span>
  <span class="Delimiter">}</span>
  <span class="Comment"># return chan.first-full == tmp</span>
  full:number<span class="Special"> &lt;- </span>get chan:address:channel/deref, first-full:offset
  result:boolean<span class="Special"> &lt;- </span>equal full:number, tmp:number
  <span class="Identifier">reply</span> result:boolean
]

<span class="Comment"># result:number &lt;- channel-capacity chan:address:channel</span>
recipe channel-capacity [
  default-space:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
  chan:address:channel<span class="Special"> &lt;- </span>next-ingredient
  q:address:array:location<span class="Special"> &lt;- </span>get chan:address:channel/deref, data:offset
  result:number<span class="Special"> &lt;- </span>length q:address:array:location/deref
  <span class="Identifier">reply</span> result:number
]

scenario channel-new-empty-not-full [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">3:literal/capacity</span>
    2:boolean<span class="Special"> &lt;- </span>channel-empty? 1:address:channel
    3:boolean<span class="Special"> &lt;- </span>channel-full? 1:address:channel
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>1  <span class="Comment"># empty?</span>
    3<span class="Special"> &lt;- </span>0  <span class="Comment"># full?</span>
  ]
]

scenario channel-write-not-empty [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">3:literal/capacity</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    2:boolean<span class="Special"> &lt;- </span>channel-empty? 1:address:channel
    3:boolean<span class="Special"> &lt;- </span>channel-full? 1:address:channel
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>0  <span class="Comment"># empty?</span>
    3<span class="Special"> &lt;- </span>0  <span class="Comment"># full?</span>
  ]
]

scenario channel-write-full [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">1:literal/capacity</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    2:boolean<span class="Special"> &lt;- </span>channel-empty? 1:address:channel
    3:boolean<span class="Special"> &lt;- </span>channel-full? 1:address:channel
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>0  <span class="Comment"># empty?</span>
    3<span class="Special"> &lt;- </span>1  <span class="Comment"># full?</span>
  ]
]

scenario channel-read-not-full [
  run [
    1:address:channel<span class="Special"> &lt;- </span>init-channel <span class="Constant">1:literal/capacity</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">34:literal</span>
    _, 1:address:channel<span class="Special"> &lt;- </span>read 1:address:channel
    2:boolean<span class="Special"> &lt;- </span>channel-empty? 1:address:channel
    3:boolean<span class="Special"> &lt;- </span>channel-full? 1:address:channel
  ]
  memory-should-contain [
    2<span class="Special"> &lt;- </span>1  <span class="Comment"># empty?</span>
    3<span class="Special"> &lt;- </span>0  <span class="Comment"># full?</span>
  ]
]

<span class="Comment"># helper for channels of characters in particular</span>
<span class="Comment"># out:address:channel &lt;- buffer-lines in:address:channel, out:address:channel</span>
recipe buffer-lines [
  default-space:address:address:array:location<span class="Special"> &lt;- </span>new location:type, <span class="Constant">30:literal</span>
<span class="CommentedCode">#?   $print [buffer-lines: aaa</span>
<span class="CommentedCode">#? ]</span>
  in:address:channel<span class="Special"> &lt;- </span>next-ingredient
  out:address:channel<span class="Special"> &lt;- </span>next-ingredient
  <span class="Comment"># repeat forever</span>
  <span class="Delimiter">{</span>
    line:address:buffer<span class="Special"> &lt;- </span>init-buffer, <span class="Constant">30:literal</span>
    <span class="Comment"># read characters from 'in' until newline, copy into line</span>
    <span class="Delimiter">{</span>
     <span class="Identifier"> +next-character</span>
      c:character, in:address:channel<span class="Special"> &lt;- </span>read in:address:channel
      <span class="Comment"># drop a character on backspace</span>
      <span class="Delimiter">{</span>
        <span class="Comment"># special-case: if it's a backspace</span>
        backspace?:boolean<span class="Special"> &lt;- </span>equal c:character, <span class="Constant">8:literal</span>
        <span class="Identifier">break-unless</span> backspace?:boolean
        <span class="Comment"># drop previous character</span>
<span class="CommentedCode">#?         return-to-console #? 2</span>
<span class="CommentedCode">#?         $print [backspace! #? 1</span>
<span class="CommentedCode">#? ] #? 1</span>
        <span class="Delimiter">{</span>
          buffer-length:address:number<span class="Special"> &lt;- </span>get-address line:address:buffer/deref, length:offset
          buffer-empty?:boolean<span class="Special"> &lt;- </span>equal buffer-length:address:number/deref, <span class="Constant">0:literal</span>
          <span class="Identifier">break-if</span> buffer-empty?:boolean
<span class="CommentedCode">#?           $print [before: ], buffer-length:address:number/deref, [ </span>
<span class="CommentedCode">#? ] #? 1</span>
          buffer-length:address:number/deref<span class="Special"> &lt;- </span>subtract buffer-length:address:number/deref, <span class="Constant">1:literal</span>
<span class="CommentedCode">#?           $print [after: ], buffer-length:address:number/deref, [ </span>
<span class="CommentedCode">#? ] #? 1</span>
        <span class="Delimiter">}</span>
<span class="CommentedCode">#?         $exit #? 2</span>
        <span class="Comment"># and don't append this one</span>
        <span class="Identifier">loop</span><span class="Identifier"> +next-character</span>:label
      <span class="Delimiter">}</span>
      <span class="Comment"># append anything else</span>
<span class="CommentedCode">#?       $print [buffer-lines: appending ], c:character, [ </span>
<span class="CommentedCode">#? ]</span>
      line:address:buffer<span class="Special"> &lt;- </span>buffer-append line:address:buffer, c:character
      line-done?:boolean<span class="Special"> &lt;- </span>equal c:character, <span class="Constant">10:literal/newline</span>
      <span class="Identifier">break-if</span> line-done?:boolean
      <span class="Comment"># stop buffering on eof (currently only generated by fake keyboard)</span>
      empty-fake-keyboard?:boolean<span class="Special"> &lt;- </span>equal c:character, <span class="Constant">0:literal/eof</span>
      <span class="Identifier">break-if</span> empty-fake-keyboard?:boolean
      <span class="Identifier">loop</span>
    <span class="Delimiter">}</span>
<span class="CommentedCode">#?     return-to-console #? 1</span>
    <span class="Comment"># copy line into 'out'</span>
<span class="CommentedCode">#?     $print [buffer-lines: emitting</span>
<span class="CommentedCode">#? ]</span>
    i:number<span class="Special"> &lt;- </span>copy <span class="Constant">0:literal</span>
    line-contents:address:array:character<span class="Special"> &lt;- </span>get line:address:buffer/deref, data:offset
    max:number<span class="Special"> &lt;- </span>get line:address:buffer/deref, length:offset
    <span class="Delimiter">{</span>
      done?:boolean<span class="Special"> &lt;- </span>greater-or-equal i:number, max:number
      <span class="Identifier">break-if</span> done?:boolean
      c:character<span class="Special"> &lt;- </span>index line-contents:address:array:character/deref, i:number
      out:address:channel<span class="Special"> &lt;- </span>write out:address:channel, c:character
<span class="CommentedCode">#?       $print [writing ], i:number, [: ], c:character, [ </span>
<span class="CommentedCode">#? ] #? 1</span>
      i:number<span class="Special"> &lt;- </span>add i:number, <span class="Constant">1:literal</span>
      <span class="Identifier">loop</span>
    <span class="Delimiter">}</span>
<span class="CommentedCode">#?     $dump-trace #? 1</span>
<span class="CommentedCode">#?     $exit #? 1</span>
    <span class="Identifier">loop</span>
  <span class="Delimiter">}</span>
  <span class="Identifier">reply</span> out:address:channel/same-as-ingredient:1
]

scenario buffer-lines-blocks-until-newline [
  run [
    1:address:channel/stdin<span class="Special"> &lt;- </span>init-channel <span class="Constant">10:literal/capacity</span>
    2:address:channel/buffered-stdin<span class="Special"> &lt;- </span>init-channel <span class="Constant">10:literal/capacity</span>
    3:boolean<span class="Special"> &lt;- </span>channel-empty? 2:address:channel/buffered-stdin
    assert 3:boolean, [
F buffer-lines-blocks-until-newline: channel should be empty after init]
    <span class="Comment"># buffer stdin into buffered-stdin, try to read from buffered-stdin</span>
    4:number/buffer-routine<span class="Special"> &lt;- </span>start-running buffer-lines:recipe, 1:address:channel/stdin, 2:address:channel/buffered-stdin
    wait-for-routine 4:number/buffer-routine
    5:boolean<span class="Special"> &lt;- </span>channel-empty? 2:address:channel/buffered-stdin
    assert 5:boolean, [
F buffer-lines-blocks-until-newline: channel should be empty after buffer-lines bring-up]
    <span class="Comment"># write 'a'</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">97:literal/a</span>
    restart 4:number/buffer-routine
    wait-for-routine 4:number/buffer-routine
    6:boolean<span class="Special"> &lt;- </span>channel-empty? 2:address:channel/buffered-stdin
    assert 6:boolean, [
F buffer-lines-blocks-until-newline: channel should be empty after writing<span class="Identifier"> 'a</span>']
    <span class="Comment"># write 'b'</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">98:literal/b</span>
    restart 4:number/buffer-routine
    wait-for-routine 4:number/buffer-routine
    7:boolean<span class="Special"> &lt;- </span>channel-empty? 2:address:channel/buffered-stdin
    assert 7:boolean, [
F buffer-lines-blocks-until-newline: channel should be empty after writing<span class="Identifier"> 'b</span>']
    <span class="Comment"># write newline</span>
    1:address:channel<span class="Special"> &lt;- </span>write 1:address:channel, <span class="Constant">10:literal/newline</span>
    restart 4:number/buffer-routine
    wait-for-routine 4:number/buffer-routine
    8:boolean<span class="Special"> &lt;- </span>channel-empty? 2:address:channel/buffered-stdin
    9:boolean/completed?<span class="Special"> &lt;- </span>not 8:boolean
    assert 9:boolean/completed?, [
F buffer-lines-blocks-until-newline: channel should contain data after writing newline]
    trace <span class="Constant">[test]</span>, <span class="Constant">[reached end]</span>
  ]
  trace-should-contain [
    test: reached end
  ]
]
</pre>
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