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1 | /* Wait on a condition. Generic version. |
2 | Copyright (C) 2000-2018 Free Software Foundation, Inc. | |
3 | This file is part of the GNU C Library. | |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Library General Public License as | |
7 | published by the Free Software Foundation; either version 2 of the | |
8 | License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Library General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Library General Public | |
16 | License along with the GNU C Library; see the file COPYING.LIB. If | |
17 | not, see <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | #include <pthread.h> | |
20 | ||
21 | #include <pt-internal.h> | |
22 | ||
23 | extern int __pthread_cond_timedwait_internal (pthread_cond_t *cond, | |
24 | pthread_mutex_t *mutex, | |
25 | const struct timespec *abstime); | |
26 | ||
27 | int | |
28 | __pthread_cond_timedwait (pthread_cond_t *cond, | |
29 | pthread_mutex_t *mutex, | |
30 | const struct timespec *abstime) | |
31 | { | |
32 | return __pthread_cond_timedwait_internal (cond, mutex, abstime); | |
33 | } | |
34 | ||
35 | strong_alias (__pthread_cond_timedwait, pthread_cond_timedwait); | |
36 | ||
37 | struct cancel_ctx | |
38 | { | |
39 | struct __pthread *wakeup; | |
40 | pthread_cond_t *cond; | |
41 | }; | |
42 | ||
43 | static void | |
44 | cancel_hook (void *arg) | |
45 | { | |
46 | struct cancel_ctx *ctx = arg; | |
47 | struct __pthread *wakeup = ctx->wakeup; | |
48 | pthread_cond_t *cond = ctx->cond; | |
49 | int unblock; | |
50 | ||
51 | __pthread_spin_lock (&cond->__lock); | |
52 | /* The thread only needs to be awaken if it's blocking or about to block. | |
53 | If it was already unblocked, it's not queued any more. */ | |
54 | unblock = wakeup->prevp != NULL; | |
55 | if (unblock) | |
56 | __pthread_dequeue (wakeup); | |
57 | __pthread_spin_unlock (&cond->__lock); | |
58 | ||
59 | if (unblock) | |
60 | __pthread_wakeup (wakeup); | |
61 | } | |
62 | ||
63 | /* Block on condition variable COND until ABSTIME. As a GNU | |
64 | extension, if ABSTIME is NULL, then wait forever. MUTEX should be | |
65 | held by the calling thread. On return, MUTEX will be held by the | |
66 | calling thread. */ | |
67 | int | |
68 | __pthread_cond_timedwait_internal (pthread_cond_t *cond, | |
69 | pthread_mutex_t *mutex, | |
70 | const struct timespec *abstime) | |
71 | { | |
72 | error_t err; | |
73 | int cancelled, oldtype, drain; | |
74 | clockid_t clock_id = __pthread_default_condattr.__clock; | |
75 | ||
76 | if (abstime && (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)) | |
77 | return EINVAL; | |
78 | ||
79 | struct __pthread *self = _pthread_self (); | |
80 | struct cancel_ctx ctx; | |
81 | ctx.wakeup = self; | |
82 | ctx.cond = cond; | |
83 | ||
84 | /* Test for a pending cancellation request, switch to deferred mode for | |
85 | safer resource handling, and prepare the hook to call in case we're | |
86 | cancelled while blocking. Once CANCEL_LOCK is released, the cancellation | |
87 | hook can be called by another thread at any time. Whatever happens, | |
88 | this function must exit with MUTEX locked. | |
89 | ||
90 | This function contains inline implementations of pthread_testcancel and | |
91 | pthread_setcanceltype to reduce locking overhead. */ | |
92 | __pthread_mutex_lock (&self->cancel_lock); | |
93 | cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE) | |
94 | && self->cancel_pending; | |
95 | ||
96 | if (!cancelled) | |
97 | { | |
98 | self->cancel_hook = cancel_hook; | |
99 | self->cancel_hook_arg = &ctx; | |
100 | oldtype = self->cancel_type; | |
101 | ||
102 | if (oldtype != PTHREAD_CANCEL_DEFERRED) | |
103 | self->cancel_type = PTHREAD_CANCEL_DEFERRED; | |
104 | ||
105 | /* Add ourselves to the list of waiters. This is done while setting | |
106 | the cancellation hook to simplify the cancellation procedure, i.e. | |
107 | if the thread is queued, it can be cancelled, otherwise it is | |
108 | already unblocked, progressing on the return path. */ | |
109 | __pthread_spin_lock (&cond->__lock); | |
110 | __pthread_enqueue (&cond->__queue, self); | |
111 | if (cond->__attr != NULL) | |
112 | clock_id = cond->__attr->__clock; | |
113 | __pthread_spin_unlock (&cond->__lock); | |
114 | } | |
115 | __pthread_mutex_unlock (&self->cancel_lock); | |
116 | ||
117 | if (cancelled) | |
118 | pthread_exit (PTHREAD_CANCELED); | |
119 | ||
120 | /* Release MUTEX before blocking. */ | |
121 | __pthread_mutex_unlock (mutex); | |
122 | ||
123 | /* Block the thread. */ | |
124 | if (abstime != NULL) | |
125 | err = __pthread_timedblock (self, abstime, clock_id); | |
126 | else | |
127 | { | |
128 | err = 0; | |
129 | __pthread_block (self); | |
130 | } | |
131 | ||
132 | __pthread_spin_lock (&cond->__lock); | |
133 | if (self->prevp == NULL) | |
134 | { | |
135 | /* Another thread removed us from the list of waiters, which means a | |
136 | wakeup message has been sent. It was either consumed while we were | |
137 | blocking, or queued after we timed out and before we acquired the | |
138 | condition lock, in which case the message queue must be drained. */ | |
139 | if (!err) | |
140 | drain = 0; | |
141 | else | |
142 | { | |
143 | assert (err == ETIMEDOUT); | |
144 | drain = 1; | |
145 | } | |
146 | } | |
147 | else | |
148 | { | |
149 | /* We're still in the list of waiters. Noone attempted to wake us up, | |
150 | i.e. we timed out. */ | |
151 | assert (err == ETIMEDOUT); | |
152 | __pthread_dequeue (self); | |
153 | drain = 0; | |
154 | } | |
155 | __pthread_spin_unlock (&cond->__lock); | |
156 | ||
157 | if (drain) | |
158 | __pthread_block (self); | |
159 | ||
160 | /* We're almost done. Remove the unblock hook, restore the previous | |
161 | cancellation type, and check for a pending cancellation request. */ | |
162 | __pthread_mutex_lock (&self->cancel_lock); | |
163 | self->cancel_hook = NULL; | |
164 | self->cancel_hook_arg = NULL; | |
165 | self->cancel_type = oldtype; | |
166 | cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE) | |
167 | && self->cancel_pending; | |
168 | __pthread_mutex_unlock (&self->cancel_lock); | |
169 | ||
170 | /* Reacquire MUTEX before returning/cancelling. */ | |
171 | __pthread_mutex_lock (mutex); | |
172 | ||
173 | if (cancelled) | |
174 | pthread_exit (PTHREAD_CANCELED); | |
175 | ||
176 | return err; | |
177 | } |