pthread_cond.cpp revision 9e79af3b61b5a617c537862ebe72248beff58f19 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <pthread.h>
30
31#include <errno.h>
32#include <limits.h>
33#include <sys/atomics.h>
34#include <sys/mman.h>
35#include <unistd.h>
36
37#include "pthread_internal.h"
38
39#include "private/bionic_atomic_inline.h"
40#include "private/bionic_futex.h"
41#include "private/bionic_time_conversions.h"
42#include "private/bionic_tls.h"
43#include "private/thread_private.h"
44
45int pthread_condattr_init(pthread_condattr_t* attr) {
46  if (attr == NULL) {
47    return EINVAL;
48  }
49  *attr = PTHREAD_PROCESS_PRIVATE;
50  return 0;
51}
52
53int pthread_condattr_getpshared(const pthread_condattr_t* attr, int* pshared) {
54  if (attr == NULL || pshared == NULL) {
55    return EINVAL;
56  }
57  *pshared = *attr;
58  return 0;
59}
60
61int pthread_condattr_setpshared(pthread_condattr_t* attr, int pshared) {
62  if (attr == NULL) {
63    return EINVAL;
64  }
65  if (pshared != PTHREAD_PROCESS_SHARED && pshared != PTHREAD_PROCESS_PRIVATE) {
66    return EINVAL;
67  }
68  *attr = pshared;
69  return 0;
70}
71
72int pthread_condattr_destroy(pthread_condattr_t* attr) {
73  if (attr == NULL) {
74    return EINVAL;
75  }
76  *attr = 0xdeada11d;
77  return 0;
78}
79
80// We use one bit in condition variable values as the 'shared' flag
81// The rest is a counter.
82#define COND_SHARED_MASK        0x0001
83#define COND_COUNTER_INCREMENT  0x0002
84#define COND_COUNTER_MASK       (~COND_SHARED_MASK)
85
86#define COND_IS_SHARED(c)  (((c)->value & COND_SHARED_MASK) != 0)
87
88// XXX *technically* there is a race condition that could allow
89// XXX a signal to be missed.  If thread A is preempted in _wait()
90// XXX after unlocking the mutex and before waiting, and if other
91// XXX threads call signal or broadcast UINT_MAX/2 times (exactly),
92// XXX before thread A is scheduled again and calls futex_wait(),
93// XXX then the signal will be lost.
94
95int pthread_cond_init(pthread_cond_t* cond, const pthread_condattr_t* attr) {
96  if (cond == NULL) {
97    return EINVAL;
98  }
99
100  cond->value = 0;
101
102  if (attr != NULL && *attr == PTHREAD_PROCESS_SHARED) {
103    cond->value |= COND_SHARED_MASK;
104  }
105
106  return 0;
107}
108
109int pthread_cond_destroy(pthread_cond_t* cond) {
110  if (cond == NULL) {
111    return EINVAL;
112  }
113
114  cond->value = 0xdeadc04d;
115  return 0;
116}
117
118// This function is used by pthread_cond_broadcast and
119// pthread_cond_signal to atomically decrement the counter
120// then wake up 'counter' threads.
121static int __pthread_cond_pulse(pthread_cond_t* cond, int counter) {
122  if (__predict_false(cond == NULL)) {
123    return EINVAL;
124  }
125
126  long flags = (cond->value & ~COND_COUNTER_MASK);
127  while (true) {
128    long old_value = cond->value;
129    long new_value = ((old_value - COND_COUNTER_INCREMENT) & COND_COUNTER_MASK) | flags;
130    if (__bionic_cmpxchg(old_value, new_value, &cond->value) == 0) {
131      break;
132    }
133  }
134
135  // Ensure that all memory accesses previously made by this thread are
136  // visible to the woken thread(s).  On the other side, the "wait"
137  // code will issue any necessary barriers when locking the mutex.
138  //
139  // This may not strictly be necessary -- if the caller follows
140  // recommended practice and holds the mutex before signaling the cond
141  // var, the mutex ops will provide correct semantics.  If they don't
142  // hold the mutex, they're subject to race conditions anyway.
143  ANDROID_MEMBAR_FULL();
144
145  __futex_wake_ex(&cond->value, COND_IS_SHARED(cond), counter);
146  return 0;
147}
148
149__LIBC_HIDDEN__
150int __pthread_cond_timedwait_relative(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* reltime) {
151  int old_value = cond->value;
152
153  pthread_mutex_unlock(mutex);
154  int status = __futex_wait_ex(&cond->value, COND_IS_SHARED(cond), old_value, reltime);
155  pthread_mutex_lock(mutex);
156
157  if (status == -ETIMEDOUT) {
158    return ETIMEDOUT;
159  }
160  return 0;
161}
162
163__LIBC_HIDDEN__
164int __pthread_cond_timedwait(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime, clockid_t clock) {
165  timespec ts;
166  timespec* tsp;
167
168  if (abstime != NULL) {
169    if (__timespec_to_absolute(&ts, abstime, clock) < 0) {
170      return ETIMEDOUT;
171    }
172    tsp = &ts;
173  } else {
174    tsp = NULL;
175  }
176
177  return __pthread_cond_timedwait_relative(cond, mutex, tsp);
178}
179
180int pthread_cond_broadcast(pthread_cond_t* cond) {
181  return __pthread_cond_pulse(cond, INT_MAX);
182}
183
184int pthread_cond_signal(pthread_cond_t* cond) {
185  return __pthread_cond_pulse(cond, 1);
186}
187
188int pthread_cond_wait(pthread_cond_t* cond, pthread_mutex_t* mutex) {
189  return __pthread_cond_timedwait(cond, mutex, NULL, CLOCK_REALTIME);
190}
191
192int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t * mutex, const timespec *abstime) {
193  return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_REALTIME);
194}
195
196// TODO: this exists only for backward binary compatibility.
197int pthread_cond_timedwait_monotonic(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime) {
198  return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_MONOTONIC);
199}
200
201int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime) {
202  return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_MONOTONIC);
203}
204
205int pthread_cond_timedwait_relative_np(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* reltime) {
206  return __pthread_cond_timedwait_relative(cond, mutex, reltime);
207}
208
209int pthread_cond_timeout_np(pthread_cond_t* cond, pthread_mutex_t* mutex, unsigned ms) {
210  timespec ts;
211  timespec_from_ms(ts, ms);
212  return __pthread_cond_timedwait_relative(cond, mutex, &ts);
213}
214