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
|
; Part of Scheme 48 1.9. See file COPYING for notices and license.
; Authors: Richard Kelsey, Jonathan Rees, Mike Sperber
; Channel interrupt stuff.
; Block reads and writes in terms of partial reads and writes.
; CHANNEL-READ returns the number of characters read or the EOF object.
; BUFFER is either a string or byte vector and START is the index at which
; to place the first character read. COUNT is the maximum number of characters
; that may be read. If WAIT? is true the thread should block if nothing
; is immediately available.
; We disable interrupts to be sure that we have installed CONDVAR before
; any completion interrupt arrives.
;
; Like all maybe-commits, this returns #T if it successfully committed and
; #F if the commit failed.
(define (channel-maybe-commit-and-read channel buffer start count condvar wait?)
(maybe-commit-no-interrupts
(lambda ()
(let ((got (channel-maybe-read channel buffer start count wait?)))
(cond
((not got)
(add-channel-condvar! channel condvar))
((cell? got)
(note-channel-result! condvar
(make-read/write-i/o-error 'channel-maybe-read
(cell-ref got)
channel buffer start count wait?)))
(else
(note-channel-result! condvar got)))))))
(define (channel-maybe-commit-and-write channel buffer start count condvar wait?)
(maybe-commit-no-interrupts
(lambda ()
(let ((got (channel-maybe-write channel buffer start count)))
(cond
((not got)
(add-channel-condvar! channel condvar)
(if wait?
(with-new-proposal (lose)
(maybe-commit-and-wait-for-condvar condvar #f))))
((cell? got)
(note-channel-result! condvar
(make-read/write-i/o-error 'channel-maybe-write
(cell-ref got)
channel buffer start count wait?)))
(else
(note-channel-result! condvar got)))))))
(define (make-read/write-i/o-error who status channel buffer start count wait?)
(condition
(make-i/o-error)
(make-os-error status)
(make-who-condition who)
(make-message-condition
(os-string->string
(byte-vector->os-string
(os-error-message status))))
(make-irritants-condition (list channel buffer start count wait?))))
; Set CONDVAR's value to be RESULT.
(define (note-channel-result! condvar result)
(with-new-proposal (lose)
(or (maybe-commit-and-set-condvar! condvar result)
(lose))))
; Used for stderr, which is unbuffered both here and in C.
(define (channel-write channel buffer start count)
(let ((ints (disable-interrupts!)))
(let ((res (channel-maybe-write channel buffer start count)))
(if res
(begin
(set-enabled-interrupts! ints)
res)
(let ((condvar (make-condvar)))
(add-channel-condvar! channel condvar)
(with-new-proposal (lose)
(or (maybe-commit-and-wait-for-condvar condvar #f)
(lose)))
(set-enabled-interrupts! ints)
(condvar-value condvar))))))
;----------------
(define (channel-maybe-commit-and-close channel close-channel)
(maybe-commit-no-interrupts
(lambda ()
(let ((condvar (fetch-channel-condvar! channel)))
(if condvar
(begin
(channel-abort channel)
(close-channel channel)
(note-channel-result! condvar
(if (input-channel? channel)
(eof-object)
0)))
(close-channel channel))))))
(define (input-channel? channel)
(= (channel-status channel)
(enum channel-status-option input)))
;----------------
; Install an interrupt handler that queues up the results of completed I/O
; operations and spawn a thread to cope with them. This is written so as
; to avoid having state in top-level variables, because their values are
; saved in dumped images.
(define (initialize-channel-i/o!)
(session-data-set! channel-wait-condvars-slot '())
(set-interrupt-handler! (enum interrupt i/o-completion)
i/o-completion-handler))
; The warning message is printed using DEBUG-MESSAGE because to try to make
; sure it appears in spite of whatever problem's the I/O system is having.
;
; Called with interrupts disabled.
(define (i/o-completion-handler channel error? status enabled-interrupts)
(let ((condvar (fetch-channel-condvar! channel)))
(if condvar
(note-channel-result! condvar
(if error?
(condition
(make-i/o-error)
(make-who-condition 'i/o-completion-handler)
(make-message-condition (os-error-message status))
(make-irritants-condition (list channel enabled-interrupts)))
status)))))
; Exported procedure
(define (zap-i/o-orphans!)
(abort-unwanted-reads!)
(not (null? (channel-condvars))))
;----------------
; A session slot contains an alist mapping channels to condvars for the result
; of an i/o operation on that channel.
(define channel-wait-condvars-slot
(make-session-data-slot! '()))
(define (channel-condvars)
(session-data-ref channel-wait-condvars-slot))
(define (set-channel-condvars! condvars)
(session-data-set! channel-wait-condvars-slot condvars))
; Adding a condvar and channel - the caller has already determined there is no
; existing condvar for this channel.
(define (add-channel-condvar! channel condvar)
(set-channel-condvars! (cons (cons channel condvar)
(channel-condvars))))
; Exported interface.
(define wait-for-channel add-channel-condvar!)
; This just deletes from the alist.
(define (fetch-channel-condvar! channel)
(let ((condvars (channel-condvars)))
(cond ((null? condvars)
#f)
((eq? channel (caar condvars))
(set-channel-condvars! (cdr condvars))
(cdar condvars))
(else
(let loop ((condvars (cdr condvars)) (prev condvars))
(cond ((null? condvars)
#f)
((eq? channel (caar condvars))
(set-cdr! prev (cdr condvars))
(cdar condvars))
(else
(loop (cdr condvars) condvars))))))))
; Abort the read operations for any channel whose condvar no longer has waiters.
; The main purpose of ABORT-UNWANTED-READS is to abort reads after the
; reading threads have died. The Scheme process sticks around until
; all I/O has been completed and there is no point in waiting for a
; read if no one wants the result.
; One upon a time, the intention was to have this procedure abort
; unwanted writes as well. However, we must not abort writes which
; come from the automatic buffer flushing routine, which is hard to
; detect here. Moreover, the automatic buffer flushing is currently
; hard to abort.
(define (abort-unwanted-reads!)
(let ((ints (disable-interrupts!)))
(let loop ((condvars (channel-condvars)) (okay '()))
(if (null? condvars)
(begin
(set-channel-condvars! okay)
(set-enabled-interrupts! ints))
(let ((condvar (cdar condvars)))
(loop (cdr condvars)
(if (or (not (input-channel? (caar condvars)))
(condvar-has-waiters? condvar))
(cons (car condvars) okay)
(begin
(channel-abort (caar condvars))
(note-channel-result! condvar 0)
okay))))))))
|
