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
|
;; Parallel Concurrent ML for Guile
;;;; Copyright (C) 2016 Andy Wingo <wingo@pobox.com>
;;;;
;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; An implementation of Parallel Concurrent ML following the 2009
;;; ICFP paper "Parallel Concurrent ML" by John Reppy, Claudio
;;; V. Russo, and Yingqui Xiao.
;;;
;;; This implementation differs from the paper in a few ways:
;;;
;;; * Superficially, We use the term "operation" instead of "event".
;;; We say "wrap-operation" instead of "wrap", "choice-operation"
;;; instead of "choose", and "perform-operation" instead of "sync".
;;;
;;; * For the moment, this is an implementation of "primitive CML"
;;; only. This may change in the future.
;;;
;;; * The continuation handling is a little different; in Manticore
;;; (or at least in the paper), it appears that suspended threads
;;; are represented in a quite raw way, whereas in Guile there are
;;; wrapper <fiber> objects. Likewise unlike in CML, the
;;; continuations in Fibers are delimited and composable, so things
;;; are a little different. Suspended computations expect to be
;;; passed a thunk as the resume value, and that thunk gets invoked
;;; in the context of the fiber. For this reason we represent
;;; wrappers explicitly in events, using them to wrap the resume
;;; thunks. As in the C# implementation, we delay continuation
;;; creation / fiber suspension until after a failed "doFn" phase.
;;;
;;; * In Fibers we do away with the "poll" phase, instead merging it
;;; with the "try" phase. (Our "try" phase is more like what CML
;;; calls "do". In Fibers, there is no do; there is only try.)
;;;
(define-module (fibers operations)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-9 gnu)
#:use-module (ice-9 atomic)
#:use-module (ice-9 match)
#:use-module ((ice-9 threads)
#:select (current-thread
make-mutex make-condition-variable
lock-mutex unlock-mutex
wait-condition-variable signal-condition-variable))
#:use-module (fibers internal)
#:export (wrap-operation
choice-operation
perform-operation
make-base-operation))
;; Three possible values: W (waiting), C (claimed), or S (synched).
;; The meanings are as in the Parallel CML paper.
(define-inlinable (make-op-state) (make-atomic-box 'W))
(define-record-type <base-op>
(make-base-operation wrap-fn try-fn block-fn)
base-op?
;; ((arg ...) -> (result ...)) | #f
(wrap-fn base-op-wrap-fn)
;; () -> (thunk | #f)
(try-fn base-op-try-fn)
;; (op-state sched resume-k) -> ()
(block-fn base-op-block-fn))
(define-record-type <choice-op>
(make-choice-operation base-ops)
choice-op?
(base-ops choice-op-base-ops))
(define (wrap-operation op f)
"Given the operation @var{op}, return a new operation that, if and
when it succeeds, will apply @var{f} to the values yielded by
performing @var{op}, and yield the result as the values of the wrapped
operation."
(match op
(($ <base-op> wrap-fn try-fn block-fn)
(make-base-operation (match wrap-fn
(#f f)
(_ (lambda args
(call-with-values (lambda ()
(apply wrap-fn args))
f))))
try-fn
block-fn))
(($ <choice-op> base-ops)
(let* ((count (vector-length base-ops))
(base-ops* (make-vector count)))
(let lp ((i 0))
(when (< i count)
(vector-set! base-ops* i (wrap-operation (vector-ref base-ops i) f))
(lp (1+ i))))
(make-choice-operation base-ops*)))))
(define (choice-operation . ops)
"Given the operations @var{ops}, return a new operation that if it
succeeds, will succeed with one and only one of the sub-operations
@var{ops}."
(define (flatten ops)
(match ops
(() '())
((op . ops)
(append (match op
(($ <base-op>) (list op))
(($ <choice-op> base-ops) (vector->list base-ops)))
(flatten ops)))))
(match (flatten ops)
((base-op) base-op)
(base-ops (make-choice-operation (list->vector base-ops)))))
(define (perform-operation op)
"Perform the operation @var{op} and return the resulting values. If
the operation cannot complete directly, block until it can complete."
(define (wrap-resume resume wrap-fn)
(if wrap-fn
(lambda (thunk)
(resume (lambda ()
(call-with-values thunk wrap-fn))))
resume))
(define (block sched resume)
(let ((flag (make-op-state)))
(match op
(($ <base-op> wrap-fn try-fn block-fn)
(block-fn flag sched (wrap-resume resume wrap-fn)))
(($ <choice-op> base-ops)
(let lp ((i 0))
(when (< i (vector-length base-ops))
(match (vector-ref base-ops i)
(($ <base-op> wrap-fn try-fn block-fn)
(block-fn flag sched (wrap-resume resume wrap-fn))))
(lp (1+ i))))))))
(define (suspend)
;; Two cases. If there is a current fiber, then we suspend the
;; current fiber and arrange to restart it when the operation
;; succeeds. Otherwise we block the current thread until the
;; operation succeeds, to allow for communication between fibers
;; and foreign threads.
(if (current-fiber)
(suspend-current-fiber
(lambda (fiber)
(define (resume thunk) (resume-fiber fiber thunk))
(block (fiber-scheduler fiber) resume)))
(let ((k #f)
(thread (current-thread))
(mutex (make-mutex))
(condvar (make-condition-variable)))
(define (resume thunk)
(cond
((eq? (current-thread) thread)
(set! k thunk))
(else
(lock-mutex mutex)
(set! k thunk)
(signal-condition-variable condvar)
(unlock-mutex mutex))))
(lock-mutex mutex)
(block #f resume)
(let lp ()
(cond
(k
(unlock-mutex mutex)
(k))
(else
(wait-condition-variable condvar mutex)
(lp)))))))
;; First, try to sync on an op. If no op syncs, block.
(match op
(($ <base-op> wrap-fn try-fn)
(match (try-fn)
(#f (suspend))
(thunk
(if wrap-fn
(call-with-values thunk wrap-fn)
(thunk)))))
(($ <choice-op> base-ops)
(let* ((count (vector-length base-ops))
(offset (random count)))
(let lp ((i 0))
(if (< i count)
(match (vector-ref base-ops (modulo (+ i offset) count))
(($ <base-op> wrap-fn try-fn)
(match (try-fn)
(#f (lp (1+ i)))
(thunk
(if wrap-fn
(call-with-values thunk wrap-fn)
(thunk))))))
(suspend)))))))
|
