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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 <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 3:literal/capacity
1:address:channel<span class="Special"> <- </span>write 1:address:channel, 34:literal
2:integer, 1:address:channel<span class="Special"> <- </span>read 1:address:channel
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>34
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
container channel <span class="Delimiter">[</span>
<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:integer <span class="Comment"># for write</span>
first-free:integer <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="Delimiter">]</span>
<span class="Comment"># result:address:channel <- init-channel capacity:integer</span>
recipe init-channel <span class="Delimiter">[</span>
default-space:address:array:location<span class="Special"> <- </span>new location:type, 30:literal
<span class="Comment"># result = new channel</span>
result:address:channel<span class="Special"> <- </span>new channel:type
<span class="Comment"># result.first-full = 0</span>
full:address:integer<span class="Special"> <- </span>get-address result:address:channel/deref, first-full:offset
full:address:integer/deref<span class="Special"> <- </span>copy 0:literal
<span class="Comment"># result.first-free = 0</span>
free:address:integer<span class="Special"> <- </span>get-address result:address:channel/deref, first-free:offset
free:address:integer/deref<span class="Special"> <- </span>copy 0:literal
<span class="Comment"># result.data = new location[ingredient+1]</span>
capacity:integer<span class="Special"> <- </span>next-ingredient
capacity:integer<span class="Special"> <- </span>add capacity:integer, 1:literal <span class="Comment"># unused slot for 'full?' below</span>
dest:address:address:array:location<span class="Special"> <- </span>get-address result:address:channel/deref, data:offset
dest:address:address:array:location/deref<span class="Special"> <- </span>new location:type, capacity:integer
<span class="Identifier">reply</span> result:address:channel
<span class="Delimiter">]</span>
<span class="Comment"># chan:address:channel <- write chan:address:channel, val:location</span>
recipe write <span class="Delimiter">[</span>
default-space:address:array:location<span class="Special"> <- </span>new location:type, 30:literal
chan:address:channel<span class="Special"> <- </span>next-ingredient
val:location<span class="Special"> <- </span>next-ingredient
<span class="Delimiter">{</span>
<span class="Comment"># block if chan is full</span>
full:boolean<span class="Special"> <- </span>channel-full? chan:address:channel
<span class="Identifier">break-unless</span> full:boolean
full-address:address:integer<span class="Special"> <- </span>get-address chan:address:channel/deref, first-full:offset
wait-for-location full-address:address:integer/deref
<span class="Delimiter">}</span>
<span class="Comment"># store val</span>
circular-buffer:address:array:location<span class="Special"> <- </span>get chan:address:channel/deref, data:offset
free:address:integer<span class="Special"> <- </span>get-address chan:address:channel/deref, first-free:offset
dest:address:location<span class="Special"> <- </span>index-address circular-buffer:address:array:location/deref, free:address:integer/deref
dest:address:location/deref<span class="Special"> <- </span>copy val:location
<span class="Comment"># increment free</span>
free:address:integer/deref<span class="Special"> <- </span>add free:address:integer/deref, 1:literal
<span class="Delimiter">{</span>
<span class="Comment"># wrap free around to 0 if necessary</span>
len:integer<span class="Special"> <- </span>length circular-buffer:address:array:location/deref
at-end?:boolean<span class="Special"> <- </span>greater-or-equal free:address:integer/deref, len:integer
<span class="Identifier">break-unless</span> at-end?:boolean
free:address:integer/deref<span class="Special"> <- </span>copy 0:literal
<span class="Delimiter">}</span>
<span class="Identifier">reply</span> chan:address:channel/same-as-ingredient:0
<span class="Delimiter">]</span>
<span class="Comment"># result:location, chan:address:channel <- read chan:address:channel</span>
recipe read <span class="Delimiter">[</span>
default-space:address:array:location<span class="Special"> <- </span>new location:type, 30:literal
chan:address:channel<span class="Special"> <- </span>next-ingredient
<span class="Delimiter">{</span>
<span class="Comment"># block if chan is empty</span>
empty:boolean<span class="Special"> <- </span>channel-empty? chan:address:channel
<span class="Identifier">break-unless</span> empty:boolean
free-address:address:integer<span class="Special"> <- </span>get-address chan:address:channel/deref, first-free:offset
wait-for-location free-address:address:integer/deref
<span class="Delimiter">}</span>
<span class="Comment"># read result</span>
full:address:integer<span class="Special"> <- </span>get-address chan:address:channel/deref, first-full:offset
circular-buffer:address:array:location<span class="Special"> <- </span>get chan:address:channel/deref, data:offset
result:location<span class="Special"> <- </span>index circular-buffer:address:array:location/deref, full:address:integer/deref
<span class="Comment"># increment full</span>
full:address:integer/deref<span class="Special"> <- </span>add full:address:integer/deref, 1:literal
<span class="Delimiter">{</span>
<span class="Comment"># wrap full around to 0 if necessary</span>
len:integer<span class="Special"> <- </span>length circular-buffer:address:array:location/deref
at-end?:boolean<span class="Special"> <- </span>greater-or-equal full:address:integer/deref, len:integer
<span class="Identifier">break-unless</span> at-end?:boolean
full:address:integer/deref<span class="Special"> <- </span>copy 0:literal
<span class="Delimiter">}</span>
<span class="Identifier">reply</span> result:location, chan:address:channel/same-as-ingredient:0
<span class="Delimiter">]</span>
scenario channel-initialization <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 3:literal/capacity
2:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-full:offset
3:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-free:offset
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>0 <span class="Comment"># first-full</span>
3<span class="Special"> <- </span>0 <span class="Comment"># first-free</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
scenario channel-write-increments-free <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 3:literal/capacity
1:address:channel<span class="Special"> <- </span>write 1:address:channel, 34:literal
2:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-full:offset
3:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-free:offset
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>0 <span class="Comment"># first-full</span>
3<span class="Special"> <- </span>1 <span class="Comment"># first-free</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
scenario channel-read-increments-full <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 3:literal/capacity
1:address:channel<span class="Special"> <- </span>write 1:address:channel, 34:literal
_, 1:address:channel<span class="Special"> <- </span>read 1:address:channel
2:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-full:offset
3:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-free:offset
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>1 <span class="Comment"># first-full</span>
3<span class="Special"> <- </span>1 <span class="Comment"># first-free</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
scenario channel-wrap <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
<span class="Comment"># channel with just 1 slot</span>
1:address:channel<span class="Special"> <- </span>init-channel 1:literal/capacity
<span class="Comment"># write and read a value</span>
1:address:channel<span class="Special"> <- </span>write 1:address:channel, 34:literal
_, 1:address:channel<span class="Special"> <- </span>read 1:address:channel
<span class="Comment"># first-free will now be 1</span>
2:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-free:offset
3:integer<span class="Special"> <- </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"> <- </span>write 1:address:channel, 34:literal
4:integer<span class="Special"> <- </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"> <- </span>read 1:address:channel
5:integer<span class="Special"> <- </span>get 1:address:channel/deref, first-full:offset
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>1 <span class="Comment"># first-free after first write</span>
3<span class="Special"> <- </span>1 <span class="Comment"># first-full after first read</span>
4<span class="Special"> <- </span>0 <span class="Comment"># first-free after second write, wrapped</span>
5<span class="Special"> <- </span>0 <span class="Comment"># first-full after second read, wrapped</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</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? <span class="Delimiter">[</span>
default-space:address:array:location<span class="Special"> <- </span>new location:type, 30:literal
chan:address:channel<span class="Special"> <- </span>next-ingredient
<span class="Comment"># return chan.first-full == chan.first-free</span>
full:integer<span class="Special"> <- </span>get chan:address:channel/deref, first-full:offset
free:integer<span class="Special"> <- </span>get chan:address:channel/deref, first-free:offset
result:boolean<span class="Special"> <- </span>equal full:integer, free:integer
<span class="Identifier">reply</span> result:boolean
<span class="Delimiter">]</span>
<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? <span class="Delimiter">[</span>
default-space:address:array:location<span class="Special"> <- </span>new location:type, 30:literal
chan:address:channel<span class="Special"> <- </span>next-ingredient
<span class="Comment"># tmp = chan.first-free + 1</span>
tmp:integer<span class="Special"> <- </span>get chan:address:channel/deref, first-free:offset
tmp:integer<span class="Special"> <- </span>add tmp:integer, 1:literal
<span class="Delimiter">{</span>
<span class="Comment"># if tmp == chan.capacity, tmp = 0</span>
len:integer<span class="Special"> <- </span>channel-capacity chan:address:channel
at-end?:boolean<span class="Special"> <- </span>greater-or-equal tmp:integer, len:integer
<span class="Identifier">break-unless</span> at-end?:boolean
tmp:integer<span class="Special"> <- </span>copy 0:literal
<span class="Delimiter">}</span>
<span class="Comment"># return chan.first-full == tmp</span>
full:integer<span class="Special"> <- </span>get chan:address:channel/deref, first-full:offset
result:boolean<span class="Special"> <- </span>equal full:integer, tmp:integer
<span class="Identifier">reply</span> result:boolean
<span class="Delimiter">]</span>
<span class="Comment"># result:integer <- channel-capacity chan:address:channel</span>
recipe channel-capacity <span class="Delimiter">[</span>
default-space:address:array:location<span class="Special"> <- </span>new location:type, 30:literal
chan:address:channel<span class="Special"> <- </span>next-ingredient
q:address:array:location<span class="Special"> <- </span>get chan:address:channel/deref, data:offset
result:integer<span class="Special"> <- </span>length q:address:array:location/deref
<span class="Identifier">reply</span> result:integer
<span class="Delimiter">]</span>
scenario channel-new-empty-not-full <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 3:literal/capacity
2:integer<span class="Special"> <- </span>channel-empty? 1:address:channel
3:integer<span class="Special"> <- </span>channel-full? 1:address:channel
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>1 <span class="Comment"># empty?</span>
3<span class="Special"> <- </span>0 <span class="Comment"># full?</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
scenario channel-write-not-empty <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 3:literal/capacity
1:address:channel<span class="Special"> <- </span>write 1:address:channel, 34:literal
2:integer<span class="Special"> <- </span>channel-empty? 1:address:channel
3:integer<span class="Special"> <- </span>channel-full? 1:address:channel
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>0 <span class="Comment"># empty?</span>
3<span class="Special"> <- </span>0 <span class="Comment"># full?</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
scenario channel-write-full <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 1:literal/capacity
1:address:channel<span class="Special"> <- </span>write 1:address:channel, 34:literal
2:integer<span class="Special"> <- </span>channel-empty? 1:address:channel
3:integer<span class="Special"> <- </span>channel-full? 1:address:channel
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>0 <span class="Comment"># empty?</span>
3<span class="Special"> <- </span>1 <span class="Comment"># full?</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
scenario channel-read-not-full <span class="Delimiter">[</span>
run <span class="Delimiter">[</span>
1:address:channel<span class="Special"> <- </span>init-channel 1:literal/capacity
1:address:channel<span class="Special"> <- </span>write 1:address:channel, 34:literal
_, 1:address:channel<span class="Special"> <- </span>read 1:address:channel
2:integer<span class="Special"> <- </span>channel-empty? 1:address:channel
3:integer<span class="Special"> <- </span>channel-full? 1:address:channel
<span class="Delimiter">]</span>
memory-should-contain <span class="Delimiter">[</span>
2<span class="Special"> <- </span>1 <span class="Comment"># empty?</span>
3<span class="Special"> <- </span>0 <span class="Comment"># full?</span>
<span class="Delimiter">]</span>
<span class="Delimiter">]</span>
</pre>
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