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

scenario channel [
  run [
    1:address:shared:channel <- new-channel 3/capacity
    1:address:shared:channel <- write 1:address:shared:channel, 34
    2:character, 1:address:shared:channel <- read 1:address:shared:channel
  ]
  memory-should-contain [
    2 <- 34
  ]
]

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

recipe new-channel capacity:number -> result:address:shared:channel [
  local-scope
  load-ingredients
  result <- new channel:type
  # result.first-full = 0
  full:address:number <- get-address *result, first-full:offset
  *full <- copy 0
  # result.first-free = 0
  free:address:number <- get-address *result, first-free:offset
  *free <- copy 0
  # result.data = new location[ingredient+1]
  capacity <- add capacity, 1  # unused slot for 'full?' below
  dest:address:address:shared:array:character <- get-address *result, data:offset
  *dest <- new character:type, capacity
]

recipe write chan:address:shared:channel, val:character -> chan:address:shared:channel [
  local-scope
  load-ingredients
  {
    # block if chan is full
    full:boolean <- channel-full? chan
    break-unless full
    full-address:address:number <- get-address *chan, first-full:offset
    wait-for-location *full-address
  }
  # store val
  circular-buffer:address:shared:array:character <- get *chan, data:offset
  free:address:number <- get-address *chan, first-free:offset
  dest:address:character <- index-
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