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
|
/* Linuxthreads - a simple clone()-based implementation of Posix */
/* threads for Linux. */
/* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */
/* and Pavel Krauz (krauz@fsid.cvut.cz). */
/* */
/* This program is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU Library General Public License */
/* as published by the Free Software Foundation; either version 2 */
/* of the License, or (at your option) any later version. */
/* */
/* This program 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 Library General Public License for more details. */
/* Condition variables */
#include <errno.h>
#include <sched.h>
#include <stddef.h>
#include <sys/time.h>
#include "pthread.h"
#include "internals.h"
#include "spinlock.h"
#include "queue.h"
#include "restart.h"
int pthread_cond_init(pthread_cond_t *cond,
const pthread_condattr_t *cond_attr)
{
__pthread_init_lock(&cond->__c_lock);
cond->__c_waiting = NULL;
return 0;
}
int pthread_cond_destroy(pthread_cond_t *cond)
{
if (cond->__c_waiting != NULL) return EBUSY;
return 0;
}
/* Function called by pthread_cancel to remove the thread from
waiting on a condition variable queue. */
static int cond_extricate_func(void *obj, pthread_descr th)
{
volatile pthread_descr self = thread_self();
pthread_cond_t *cond = obj;
int did_remove = 0;
__pthread_lock(&cond->__c_lock, self);
did_remove = remove_from_queue(&cond->__c_waiting, th);
__pthread_unlock(&cond->__c_lock);
return did_remove;
}
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
{
volatile pthread_descr self = thread_self();
pthread_extricate_if extr;
int already_canceled = 0;
/* Check whether the mutex is locked and owned by this thread. */
if (mutex->__m_kind != PTHREAD_MUTEX_FAST_NP && mutex->__m_owner != self)
return EINVAL;
/* Set up extrication interface */
extr.pu_object = cond;
extr.pu_extricate_func = cond_extricate_func;
/* Register extrication interface */
__pthread_set_own_extricate_if(self, &extr);
/* Atomically enqueue thread for waiting, but only if it is not
canceled. If the thread is canceled, then it will fall through the
suspend call below, and then call pthread_exit without
having to worry about whether it is still on the condition variable queue.
This depends on pthread_cancel setting p_canceled before calling the
extricate function. */
__pthread_lock(&cond->__c_lock, self);
if (!(THREAD_GETMEM(self, p_canceled)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE))
enqueue(&cond->__c_waiting, self);
else
already_canceled = 1;
__pthread_unlock(&cond->__c_lock);
if (already_canceled) {
__pthread_set_own_extricate_if(self, 0);
pthread_exit(PTHREAD_CANCELED);
}
pthread_mutex_unlock(mutex);
suspend(self);
__pthread_set_own_extricate_if(self, 0);
/* Check for cancellation again, to provide correct cancellation
point behavior */
if (THREAD_GETMEM(self, p_woken_by_cancel)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
THREAD_SETMEM(self, p_woken_by_cancel, 0);
pthread_mutex_lock(mutex);
pthread_exit(PTHREAD_CANCELED);
}
pthread_mutex_lock(mutex);
return 0;
}
static int
pthread_cond_timedwait_relative(pthread_cond_t *cond,
pthread_mutex_t *mutex,
const struct timespec * abstime)
{
volatile pthread_descr self = thread_self();
int already_canceled = 0;
pthread_extricate_if extr;
/* Check whether the mutex is locked and owned by this thread. */
if (mutex->__m_kind != PTHREAD_MUTEX_FAST_NP && mutex->__m_owner != self)
return EINVAL;
/* Set up extrication interface */
extr.pu_object = cond;
extr.pu_extricate_func = cond_extricate_func;
/* Register extrication interface */
__pthread_set_own_extricate_if(self, &extr);
/* Enqueue to wait on the condition and check for cancellation. */
__pthread_lock(&cond->__c_lock, self);
if (!(THREAD_GETMEM(self, p_canceled)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE))
enqueue(&cond->__c_waiting, self);
else
already_canceled = 1;
__pthread_unlock(&cond->__c_lock);
if (already_canceled) {
__pthread_set_own_extricate_if(self, 0);
pthread_exit(PTHREAD_CANCELED);
}
pthread_mutex_unlock(mutex);
if (!timedsuspend(self, abstime)) {
int was_on_queue;
/* __pthread_lock will queue back any spurious restarts that
may happen to it. */
__pthread_lock(&cond->__c_lock, self);
was_on_queue = remove_from_queue(&cond->__c_waiting, self);
__pthread_unlock(&cond->__c_lock);
if (was_on_queue) {
__pthread_set_own_extricate_if(self, 0);
pthread_mutex_lock(mutex);
return ETIMEDOUT;
}
/* Eat the outstanding restart() from the signaller */
suspend(self);
}
__pthread_set_own_extricate_if(self, 0);
/* The remaining logic is the same as in other cancellable waits,
such as pthread_join sem_wait or pthread_cond wait. */
if (THREAD_GETMEM(self, p_woken_by_cancel)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
THREAD_SETMEM(self, p_woken_by_cancel, 0);
pthread_mutex_lock(mutex);
pthread_exit(PTHREAD_CANCELED);
}
pthread_mutex_lock(mutex);
return 0;
}
int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex,
const struct timespec * abstime)
{
/* Indirect call through pointer! */
return pthread_cond_timedwait_relative(cond, mutex, abstime);
}
int pthread_cond_signal(pthread_cond_t *cond)
{
pthread_descr th;
__pthread_lock(&cond->__c_lock, NULL);
th = dequeue(&cond->__c_waiting);
__pthread_unlock(&cond->__c_lock);
if (th != NULL) restart(th);
return 0;
}
int pthread_cond_broadcast(pthread_cond_t *cond)
{
pthread_descr tosignal, th;
__pthread_lock(&cond->__c_lock, NULL);
/* Copy the current state of the waiting queue and empty it */
tosignal = cond->__c_waiting;
cond->__c_waiting = NULL;
__pthread_unlock(&cond->__c_lock);
/* Now signal each process in the queue */
while ((th = dequeue(&tosignal)) != NULL) restart(th);
return 0;
}
int pthread_condattr_init(pthread_condattr_t *attr)
{
return 0;
}
int pthread_condattr_destroy(pthread_condattr_t *attr)
{
return 0;
}
|
