about summary refs log tree commit diff stats
path: root/072channel.mu
blob: d391aeeb0d09804f9f4a810b6c2a71851fd3656d (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
# 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:source:number, 2:address:sink:number <- new-channel 3/capacity
    2:address:sink:number <- write 2:address:sink:number, 34
    3:number, 4:boolean, 1:address:source:number <- read 1:address:source:number
  ]
  memory-should-contain [
    3 <- 34
    4 <- 0  # read was successful
  ]
]

container channel:_elem [
  # 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:_elem
]

# Since channels have two ends, and since it's an error to use either end from
# multiple routines, let's distinguish the ends.

container source:_elem [
  chan:address:channel:_elem
]

container sink:_elem [
  chan:address:channel:_elem
]

def new-channel capacity:number -> in:address:source:_elem, out:address:sink:_elem [
  local-scope
  load-ingredients
  result:address:channel:_elem <- new {(channel _elem): type}
  *result <- put *result, first-full:offset, 0
  *result <- put *result, first-free:offset, 0
  capacity <- add capacity, 1  # unused slot for 'full?' below
  data:address:array:_elem <- new _elem:type, capacity
  *result <- put *result, data:offset, data
  in <- new {(source _elem): type}
  *in <- put *in, chan:offset, result
  out <- new {(sink _elem): type}
  *out <- put *out, chan:offset, result
]

def write out:address:sink:_elem, val:_elem -> out:address:sink:_elem [
  local-scope
  load-ingredients
  chan:address:channel:_elem <- get *out, chan:offset
  <channel-write-initial>
  {
    # block if chan is full
    full:boolean <- channel-full? chan
    break-unless full
    full-address:location <- get-location *chan, first-full:offset
    wait-for-location full-address
  }
  # store val
  circular-buffer:address:array:_elem <- get *chan, data:offset
  free:number <- get *chan, first-free:offset
  *circular-buffer <- put-index *circular-buffer, free, 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
  }
  # write back
  *chan <- put *chan, first-free:offset, free
]

def read in:address:source:_elem -> result:_elem, fail?:boolean, in:address:source:_elem [
  local-scope
  load-ingredients
  fail? <- copy 0/false  # default status
  chan:address:channel:_elem <- get *in, chan:offset
  {
    # block if chan is empty
    empty?:boolean <- channel-empty? chan
    break-unless empty?
    <channel-read-empty>
    free-address:location <- get-location *chan, first-free:offset
    wait-for-location free-address
  }
  # pull result off
  full:number <- get *chan, first-full:offset
  circular-buffer:address:array:_elem <- get *chan, data:offset
  result <- index *circular-buffer, full
  # clear the slot
  empty:address:_elem <- new _elem:type
  *circular-buffer <- put-index *circular-buffer, full, *empty
  # 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
  }
  # write back
  *chan <- put *chan, first-full:offset, full
]

def clear in:address:source:_elem -> in:address:source:_elem [
  local-scope
  load-ingredients
  chan:address:channel:_elem <- get *in, chan:offset
  {
    empty?:boolean <- channel-empty? chan
    break-if empty?
    _, _, in <- read in
  }
]

scenario channel-initialization [
  run [
    1:address:source:number <- new-channel 3/capacity
    2:address:channel:number <- get *1:address:source:number, chan:offset
    3:number <- get *2:address:channel:number, first-full:offset
    4:number <- get *2:address:channel:number, first-free:offset
  ]
  memory-should-contain [
    3 <- 0  # first-full
    4 <- 0  # first-free
  ]
]

scenario channel-write-increments-free [
  run [
    _, 1:address:sink:number <- new-channel 3/capacity
    1:address:sink:number <- write 1:address:sink:number, 34
    2:address:channel:number <- get *1:address:sink:number, chan:offset
    3:number <- get *2:address:channel:character, first-full:offset
    4:number <- get *2:address:channel:character, first-free:offset
  ]
  memory-should-contain [
    3 <- 0  # first-full
    4 <- 1  # first-free
  ]
]

scenario channel-read-increments-full [
  run [
    1:address:source:number, 2:address:sink:number <- new-channel 3/capacity
    2:address:sink:number <- write 2:address:sink:number, 34
    _, _, 1:address:source:number <- read 1:address:source:number
    3:address:channel:number <- get *1:address:source:number, chan:offset
    4:number <- get *3:address:channel:number, first-full:offset
    5:number <- get *3:address:channel:number, first-free:offset
  ]
  memory-should-contain [
    4 <- 1  # first-full
    5 <- 1  # first-free
  ]
]

scenario channel-wrap [
  run [
    # channel with just 1 slot
    1:address:source:number, 2:address:sink:number <- new-channel 1/capacity
    3:address:channel:number <- get *1:address:source:number, chan:offset
    # write and read a value
    2:address:sink:number <- write 2:address:sink:number, 34
    _, _, 1:address:source:number <- read 1:address:source:number
    # first-free will now be 1
    4:number <- get *3:address:channel:number, first-free:offset
    5:number <- get *3:address:channel:number, first-free:offset
    # write second value, verify that first-free wraps
    2:address:sink:number <- write 2:address:sink:number, 34
    6:number <- get *3:address:channel:number, first-free:offset
    # read second value, verify that first-full wraps
    _, _, 1:address:source:number <- read 1:address:source:number
    7:number <- get *3:address:channel:number, first-full:offset
  ]
  memory-should-contain [
    4 <- 1  # first-free after first write
    5 <- 1  # first-full after first read
    6 <- 0  # first-free after second write, wrapped
    7 <- 0  # first-full after second read, wrapped
  ]
]

scenario channel-new-empty-not-full [
  run [
    1:address:source:number, 2:address:sink:number <- new-channel 3/capacity
    3:address:channel:number <- get *1:address:source:number, chan:offset
    4:boolean <- channel-empty? 3:address:channel:number
    5:boolean <- channel-full? 3:address:channel:number
  ]
  memory-should-contain [
    4 <- 1  # empty?
    5 <- 0  # full?
  ]
]

scenario channel-write-not-empty [
  run [
    1:address:source:number, 2:address:sink:number <- new-channel 3/capacity
    3:address:channel:number <- get *1:address:source:number, chan:offset
    2:address:sink:number <- write 2:address:sink:number, 34
    4:boolean <- channel-empty? 3:address:channel:number
    5:boolean <- channel-full? 3:address:channel:number
  ]
  memory-should-contain [
    4 <- 0  # empty?
    5 <- 0  # full?
  ]
]

scenario channel-write-full [
  run [
    1:address:source:number, 2:address:sink:number <- new-channel 1/capacity
    3:address:channel:number <- get *1:address:source:number, chan:offset
    2:address:sink:number <- write 2:address:sink:number, 34
    4:boolean <- channel-empty? 3:address:channel:number
    5:boolean <- channel-full? 3:address:channel:number
  ]
  memory-should-contain [
    4 <- 0  # empty?
    5 <- 1  # full?
  ]
]

scenario channel-read-not-full [
  run [
    1:address:source:number, 2:address:sink:number <- new-channel 1/capacity
    3:address:channel:number <- get *1:address:source:number, chan:offset
    2:address:sink:number <- write 2:address:sink:number, 34
    _, _, 1:address:source:number <- read 1:address:source:number
    4:boolean <- channel-empty? 3:address:channel:number
    5:boolean <- channel-full? 3:address:channel:number
  ]
  memory-should-contain [
    4 <- 1  # empty?
    5 <- 0  # full?
  ]
]

## cancelling channels

# every channel comes with a boolean signifying if it's been closed
# initially this boolean is false
container channel:_elem [
  closed?:boolean
]

# a channel can be closed from either the source or the sink
# both threads can modify it, but they can only set it, so this is a benign race
def close x:address:source:_elem -> x:address:source:_elem [
  local-scope
  load-ingredients
  chan:address:channel:_elem <- get *x, chan:offset
  *chan <- put *chan, closed?:offset, 1/true
]
def close x:address:sink:_elem -> x:address:sink:_elem [
  local-scope
  load-ingredients
  chan:address:channel:_elem <- get *x, chan:offset
  *chan <- put *chan, closed?:offset, 1/true
]

# once a channel is closed from one side, no further operations are expected from that side
# if a channel is closed for reading,
#   no further writes will be let through
# if a channel is closed for writing,
#   future reads continue until the channel empties,
#   then the channel is also closed for reading
after <channel-write-initial> [
  closed?:boolean <- get *chan, closed?:offset
  return-if closed?
]

after <channel-read-empty> [
  closed?:boolean <- get *chan, closed?:offset
  {
    break-unless closed?
    empty-result:address:_elem <- new _elem:type
    return *empty-result, 1/true
  }
]

## helpers

# An empty channel has first-empty and first-full both at the same value.
def channel-empty? chan:address:channel:_elem -> 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)
def channel-full? chan:address:channel:_elem -> 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 <- 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
]

def capacity chan:address:channel:_elem -> result:number [
  local-scope
  load-ingredients
  q:address:array:_elem <- get *chan, data:offset
  result <- length *q
]

# helper for channels of characters in particular
def buffer-lines in:address:source:character, buffered-out:address:sink:character -> buffered-out:address:sink:character, in:address:source:character [
  local-scope
  load-ingredients
  # repeat forever
  eof?:boolean <- copy 0/false
  {
    line:address:buffer <- new-buffer 30
    # read characters from 'in' until newline, copy into line
    {
      +next-character
      c:character, eof?:boolean, in <- read in
      break-if eof?
      # 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:number <- get *line, length:offset
          buffer-empty?:boolean <- equal buffer-length, 0
          break-if buffer-empty?
          buffer-length <- subtract buffer-length, 1
          *line <- put *line, length:offset, buffer-length
        }
        # 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?
      loop
    }
    # copy line into 'buffered-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
      buffered-out <- write buffered-out, c
      i <- add i, 1
      loop
    }
    {
      break-unless eof?
      buffered-out <- close buffered-out
      return
    }
    loop
  }
]

scenario buffer-lines-blocks-until-newline [
  run [
    1:address:source:number, 2:address:sink:number <- new-channel 10/capacity
    _, 3:address:sink:number/buffered-stdin <- new-channel 10/capacity
    4:address:channel:number/buffered-stdin <- get *3:address:source:number, chan:offset
    5:boolean <- channel-empty? 4:address:channel:character/buffered-stdin
    assert 5:boolean, [ 
F buffer-lines-blocks-until-newline: channel should be empty after init]
    # buffer stdin into buffered-stdin, try to read from buffered-stdin
    6:number/buffer-routine <- start-running buffer-lines, 1:address:source:character/stdin, 3:address:sink:character/buffered-stdin
    wait-for-routine 6:number/buffer-routine
    7:boolean <- channel-empty? 4:address:channel:character/buffered-stdin
    assert 7:boolean, [ 
F buffer-lines-blocks-until-newline: channel should be empty after buffer-lines bring-up]
    # write 'a'
    2:address:sink:character <- write 2:address:sink:character, 97/a
    restart 6:number/buffer-routine
    wait-for-routine 6:number/buffer-routine
    8:boolean <- channel-empty? 4:address:channel:character/buffered-stdin
    assert 8:boolean, [ 
F buffer-lines-blocks-until-newline: channel should be empty after writing 'a']
    # write 'b'
    2:address:sink:character <- write 2:address:sink:character, 98/b
    restart 6:number/buffer-routine
    wait-for-routine 6:number/buffer-routine
    9:boolean <- channel-empty? 4:address:channel:character/buffered-stdin
    assert 9:boolean, [ 
F buffer-lines-blocks-until-newline: channel should be empty after writing 'b']
    # write newline
    2:address:sink:character <- write 2:address:sink:character, 10/newline
    restart 6:number/buffer-routine
    wait-for-routine 6:number/buffer-routine
    10:boolean <- channel-empty? 4:address:channel:character/buffered-stdin
    11:boolean/completed? <- not 10:boolean
    assert 11: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
  ]
]