# 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:channel <- new-channel 3/capacity
1:address:channel <- write 1:address:channel, 34
2:character, 1:address:channel <- read 1:address: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:array:character
]
# result:address:channel <- new-channel capacity:number
recipe new-channel capacity:number -> result:address: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:array:character <- get-address *result, data:offset
*dest <- new character:type, capacity
]
recipe write chan:address:channel, val:character -> chan:address: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:array:character <- get *chan, data:offset
free:address:number <- get-address *chan, first-free:offset
dest:address:character <- index-address *circular-buffer, *free
*dest <- copy val
# mark its slot as filled
*free <- add *free, 1
{
# wrap free around to 0 if necessary
len:number <- length *circular-buffer
at-end?:boolean <- greater-or-equal *free, len
break-unless at-end?
*free <- copy 0
}
]
recipe read chan:address:channel -> result:character, chan:address:channel [
local-scope
load-ingredients
{
# block if chan is empty
empty?:boolean <- channel-empty? chan
break-unless empty?
free-address:address:number <- get-address *chan, first-free:offset
wait-for-location *free-address
}
# read result
full:address:number <- get-address *chan, first-full:offset
circular-buffer:address:array:character <- get *chan, data:offset
result <- index *circular-buffer, *full
# mark its slot as empty
*full <- add *full, 1
{
# wrap full around to 0 if necessary
len:number <- length *circular-buffer
at-end?:boolean <- greater-or-equal *full, len
break-unless at-end?
*full <- copy 0
}
]
recipe clear-channel chan:address:channel -> chan:address:channel [
local-scope
load-ingredients
{
empty?:boolean <- channel-empty? chan
break-if empty?
_, chan <- read chan
}
]
scenario channel-initialization [
run [
1:address:channel <- new-channel 3/capacity
2:number <- get *1:address:channel, first-full:offset
3:number <- get *1:address:channel, first-free:offset
]
memory-should-contain [
2 <- 0 # first-full
3 <- 0 # first-free
]
]
scenario channel-write-increments-free [
run [
1:address:channel <- new-channel 3/capacity
1:address:channel <- write 1:address:channel, 34
2:number <- get *1:address:channel, first-full:offset
3:number <- get *1:address:channel, first-free:offset
]
memory-should-contain [
2 <- 0 # first-full
3 <- 1 # first-free
]
]
scenario channel-read-increments-full [
run [
1:address:channel <- new-channel 3/capacity
1:address:channel <- write 1:address:channel, 34
_, 1:address:channel <- read 1:address:channel
2:number <- get *1:address:channel, first-full:offset
3:number <- get *1:address:channel, first-free:offset
]
memory-should-contain [
2 <- 1 # first-full
3 <- 1 # first-free
]
]
scenario channel-wrap [
run [
# channel with just 1 slot
1:address:channel <- new-channel 1/capacity
# write and read a value
1:address:channel <- write 1:address:channel, 34
_, 1:address:channel <- read 1:address:channel
# first-free will now be 1
2:number <- get *1:address:channel, first-free:offset
3:number <- get *1:address:channel, first-free:offset
# write second value, verify that first-free wraps
1:address:channel <- write 1:address:channel, 34
4:number <- get *1:address:channel, first-free:offset
# read second value, verify that first-full wraps
_, 1:address:channel <- read 1:address:channel
5:number <- get *1:address:channel, first-full:offset
]
memory-should-contain [
2 <- 1 # first-free after first write
3 <- 1 # first-full after first read
4 <- 0 # first-free after second write, wrapped
5 <- 0 # first-full after second read, wrapped
]
]
## helpers
# An empty channel has first-empty and first-full both at the same value.
recipe channel-empty? chan:address:channel -> result:boolean [
local-scope
load-ingredients
# return chan.first-full == chan.first-free
full:number <- get *chan, first-full:offset
free:number <- get *chan, first-free:offset
result <- equal full, free
]
# A full channel has first-empty just before first-full, wasting one slot.
# (Other alternatives: https://en.wikipedia.org/wiki/Circular_buffer#Full_.2F_Empty_Buffer_Distinction)
recipe channel-full? chan:address:channel -> result:boolean [
local-scope
load-ingredients
# tmp = chan.first-free + 1
tmp:number <- get *chan, first-free:offset
tmp <- add tmp, 1
{
# if tmp == chan.capacity, tmp = 0
len:number <- channel-capacity chan
at-end?:boolean <- greater-or-equal tmp, len
break-unless at-end?
tmp <- copy 0
}
# return chan.first-full == tmp
full:number <- get *chan, first-full:offset
result <- equal full, tmp
]
# result:number <- channel-capacity chan:address:channel
recipe channel-capacity chan:address:channel -> result:number [
local-scope
load-ingredients
q:address:array:character <- get *chan, data:offset
result <- length *q
]
scenario channel-new-empty-not-full [
run [
1:address:channel <- new-channel 3/capacity
2:boolean <- channel-empty? 1:address:channel
3:boolean <- channel-full? 1:address:channel
]
memory-should-contain [
2 <- 1 # empty?
3 <- 0 # full?
]
]
scenario channel-write-not-empty [
run [
1:address:channel <- new-channel 3/capacity
1:address:channel <- write 1:address:channel, 34
2:boolean <- channel-empty? 1:address:channel
3:boolean <- channel-full? 1:address:channel
]
memory-should-contain [
2 <- 0 # empty?
3 <- 0 # full?
]
]
scenario channel-write-full [
run [
1:address:channel <- new-channel 1/capacity
1:address:channel <- write 1:address:channel, 34
2:boolean <- channel-empty? 1:address:channel
3:boolean <- channel-full? 1:address:channel
]
memory-should-contain [
2 <- 0 # empty?
3 <- 1 # full?
]
]
scenario channel-read-not-full [
run [
1:address:channel <- new-channel 1/capacity
1:address:channel <- write 1:address:channel, 34
_, 1:address:channel <- read 1:address:channel
2:boolean <- channel-empty? 1:address:channel
3:boolean <- channel-full? 1:address:channel
]
memory-should-contain [
2 <- 1 # empty?
3 <- 0 # full?
]
]
# helper for channels of characters in particular
recipe buffer-lines in:address:channel, out:address:channel -> out:address:channel, in:address:channel [
local-scope
load-ingredients
# repeat forever
{
line:address:buffer <- new-buffer, 30
# read characters from 'in' until newline, copy into line
{
+next-character
c:character, in <- read in
# drop a character on backspace
{
# special-case: if it's a backspace
backspace?:boolean <- equal c, 8
break-unless backspace?
# drop previous character
{
buffer-length:address:number <- get-address *line, length:offset
buffer-empty?:boolean <- equal *buffer-length, 0
break-if buffer-empty?
*buffer-length <- subtract *buffer-length, 1
}
# and don't append this one
loop +next-character:label
}
# append anything else
line <- append line, c
line-done?:boolean <- equal c, 10/newline
break-if line-done?
# stop buffering on eof (currently only generated by fake console)
eof?:boolean <- equal c, 0/eof
break-if eof?
loop
}
# copy line into 'out'
i:number <- copy 0
line-contents:address:array:character <- get *line, data:offset
max:number <- get *line, length:offset
{
done?:boolean <- greater-or-equal i, max
break-if done?
c:character <- index *line-contents, i
out <- write out, c
i <- add i, 1
loop
}
loop
}
]
scenario buffer-lines-blocks-until-newline [
run [
1:address:channel/stdin <- new-channel 10/capacity
2:address:channel/buffered-stdin <- new-channel 10/capacity
3:boolean <- channel-empty? 2:address:channel/buffered-stdin
assert 3:boolean, [
F buffer-lines-blocks-until-newline: channel should be empty after init]
# buffer stdin into buffered-stdin, try to read from buffered-stdin
4:number/buffer-routine <- start-running buffer-lines, 1:address:channel/stdin, 2:address:channel/buffered-stdin
wait-for-routine 4:number/buffer-routine
5:boolean <- 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]
# write 'a'
1:address:channel <- write 1:address:channel, 97/a
restart 4:number/buffer-routine
wait-for-routine 4:number/buffer-routine
6:boolean <- channel-empty? 2:address:channel/buffered-stdin
assert 6:boolean, [
F buffer-lines-blocks-until-newline: channel should be empty after writing 'a']
# write 'b'
1:address:channel <- write 1:address:channel, 98/b
restart 4:number/buffer-routine
wait-for-routine 4:number/buffer-routine
7:boolean <- channel-empty? 2:address:channel/buffered-stdin
assert 7:boolean, [
F buffer-lines-blocks-until-newline: channel should be empty after writing 'b']
# write newline
1:address:channel <- write 1:address:channel, 10/newline
restart 4:number/buffer-routine
wait-for-routine 4:number/buffer-routine
8:boolean <- channel-empty? 2:address:channel/buffered-stdin
9:boolean/completed? <- not 8:boolean
assert 9:boolean/completed?, [
F buffer-lines-blocks-until-newline: channel should contain data after writing newline]
trace 1, [test], [reached end]
]
trace-should-contain [
test: reached end
]
]