pthread_cond.cpp revision b676aafad04f88e36658d4468054375158dbd3c1 
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 <time.h>
36#include <unistd.h>
37
38#include "pthread_internal.h"
39
40#include "private/bionic_atomic_inline.h"
41#include "private/bionic_futex.h"
42#include "private/bionic_time_conversions.h"
43#include "private/bionic_tls.h"
44
45// We use one bit in pthread_condattr_t (long) values as the 'shared' flag
46// and one bit for the clock type (CLOCK_REALTIME is ((clockid_t) 1), and
47// CLOCK_MONOTONIC is ((clockid_t) 0).). The rest of the bits are a counter.
48//
49// The 'value' field pthread_cond_t has the same layout.
50
51#define COND_SHARED_MASK 0x0001
52#define COND_CLOCK_MASK 0x0002
53#define COND_COUNTER_STEP 0x0004
54#define COND_FLAGS_MASK (COND_SHARED_MASK | COND_CLOCK_MASK)
55#define COND_COUNTER_MASK (~COND_FLAGS_MASK)
56
57#define COND_IS_SHARED(c) (((c) & COND_SHARED_MASK) != 0)
58#define COND_GET_CLOCK(c) (((c) & COND_CLOCK_MASK) >> 1)
59#define COND_SET_CLOCK(attr, c) ((attr) | (c << 1))
60
61
62int pthread_condattr_init(pthread_condattr_t* attr) {
63  *attr = 0;
64  *attr |= PTHREAD_PROCESS_PRIVATE;
65  *attr |= (CLOCK_REALTIME << 1);
66  return 0;
67}
68
69int pthread_condattr_getpshared(const pthread_condattr_t* attr, int* pshared) {
70  *pshared = static_cast<int>(COND_IS_SHARED(*attr));
71  return 0;
72}
73
74int pthread_condattr_setpshared(pthread_condattr_t* attr, int pshared) {
75  if (pshared != PTHREAD_PROCESS_SHARED && pshared != PTHREAD_PROCESS_PRIVATE) {
76    return EINVAL;
77  }
78
79  *attr |= pshared;
80  return 0;
81}
82
83int pthread_condattr_getclock(const pthread_condattr_t* attr, clockid_t* clock) {
84  *clock = COND_GET_CLOCK(*attr);
85  return 0;
86}
87
88int pthread_condattr_setclock(pthread_condattr_t* attr, clockid_t clock) {
89  if (clock != CLOCK_MONOTONIC && clock != CLOCK_REALTIME) {
90    return EINVAL;
91  }
92
93  *attr = COND_SET_CLOCK(*attr, clock);
94  return 0;
95}
96
97int pthread_condattr_destroy(pthread_condattr_t* attr) {
98  *attr = 0xdeada11d;
99  return 0;
100}
101
102
103// XXX *technically* there is a race condition that could allow
104// XXX a signal to be missed.  If thread A is preempted in _wait()
105// XXX after unlocking the mutex and before waiting, and if other
106// XXX threads call signal or broadcast UINT_MAX/2 times (exactly),
107// XXX before thread A is scheduled again and calls futex_wait(),
108// XXX then the signal will be lost.
109
110int pthread_cond_init(pthread_cond_t* cond, const pthread_condattr_t* attr) {
111  if (attr != NULL) {
112    cond->value = (*attr & COND_FLAGS_MASK);
113  } else {
114    cond->value = 0;
115  }
116
117  return 0;
118}
119
120int pthread_cond_destroy(pthread_cond_t* cond) {
121  cond->value = 0xdeadc04d;
122  return 0;
123}
124
125// This function is used by pthread_cond_broadcast and
126// pthread_cond_signal to atomically decrement the counter
127// then wake up 'counter' threads.
128static int __pthread_cond_pulse(pthread_cond_t* cond, int counter) {
129  int flags = (cond->value & COND_FLAGS_MASK);
130  while (true) {
131    int old_value = cond->value;
132    int new_value = ((old_value - COND_COUNTER_STEP) & COND_COUNTER_MASK) | flags;
133    if (__bionic_cmpxchg(old_value, new_value, &cond->value) == 0) {
134      break;
135    }
136  }
137
138  // Ensure that all memory accesses previously made by this thread are
139  // visible to the woken thread(s).  On the other side, the "wait"
140  // code will issue any necessary barriers when locking the mutex.
141  //
142  // This may not strictly be necessary -- if the caller follows
143  // recommended practice and holds the mutex before signaling the cond
144  // var, the mutex ops will provide correct semantics.  If they don't
145  // hold the mutex, they're subject to race conditions anyway.
146  ANDROID_MEMBAR_FULL();
147
148  __futex_wake_ex(&cond->value, COND_IS_SHARED(cond->value), counter);
149  return 0;
150}
151
152__LIBC_HIDDEN__
153int __pthread_cond_timedwait_relative(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* reltime) {
154  int old_value = cond->value;
155
156  pthread_mutex_unlock(mutex);
157  int status = __futex_wait_ex(&cond->value, COND_IS_SHARED(cond->value), old_value, reltime);
158  pthread_mutex_lock(mutex);
159
160  if (status == -ETIMEDOUT) {
161    return ETIMEDOUT;
162  }
163  return 0;
164}
165
166__LIBC_HIDDEN__
167int __pthread_cond_timedwait(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime, clockid_t clock) {
168  timespec ts;
169  timespec* tsp;
170
171  if (abstime != NULL) {
172    if (__timespec_from_absolute(&ts, abstime, clock) < 0) {
173      return ETIMEDOUT;
174    }
175    tsp = &ts;
176  } else {
177    tsp = NULL;
178  }
179
180  return __pthread_cond_timedwait_relative(cond, mutex, tsp);
181}
182
183int pthread_cond_broadcast(pthread_cond_t* cond) {
184  return __pthread_cond_pulse(cond, INT_MAX);
185}
186
187int pthread_cond_signal(pthread_cond_t* cond) {
188  return __pthread_cond_pulse(cond, 1);
189}
190
191int pthread_cond_wait(pthread_cond_t* cond, pthread_mutex_t* mutex) {
192  return __pthread_cond_timedwait(cond, mutex, NULL, COND_GET_CLOCK(cond->value));
193}
194
195int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t * mutex, const timespec *abstime) {
196  return __pthread_cond_timedwait(cond, mutex, abstime, COND_GET_CLOCK(cond->value));
197}
198
199#if !defined(__LP64__)
200// TODO: this exists only for backward binary compatibility on 32 bit platforms.
201extern "C" int pthread_cond_timedwait_monotonic(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime) {
202  return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_MONOTONIC);
203}
204
205extern "C" int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* abstime) {
206  return __pthread_cond_timedwait(cond, mutex, abstime, CLOCK_MONOTONIC);
207}
208
209extern "C" int pthread_cond_timedwait_relative_np(pthread_cond_t* cond, pthread_mutex_t* mutex, const timespec* reltime) {
210  return __pthread_cond_timedwait_relative(cond, mutex, reltime);
211}
212
213extern "C" int pthread_cond_timeout_np(pthread_cond_t* cond, pthread_mutex_t* mutex, unsigned ms) {
214  timespec ts;
215  timespec_from_ms(ts, ms);
216  return __pthread_cond_timedwait_relative(cond, mutex, &ts);
217}
218#endif // !defined(__LP64__)
219