pthread_cond.cpp revision 9e6c7bc61838476d749d9bc4801777d35fd46a63
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 <stdatomic.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_futex.h" 41#include "private/bionic_time_conversions.h" 42#include "private/bionic_tls.h" 43 44// XXX *technically* there is a race condition that could allow 45// XXX a signal to be missed. If thread A is preempted in _wait() 46// XXX after unlocking the mutex and before waiting, and if other 47// XXX threads call signal or broadcast UINT_MAX/2 times (exactly), 48// XXX before thread A is scheduled again and calls futex_wait(), 49// XXX then the signal will be lost. 50 51// We use one bit in pthread_condattr_t (long) values as the 'shared' flag 52// and one bit for the clock type (CLOCK_REALTIME is ((clockid_t) 1), and 53// CLOCK_MONOTONIC is ((clockid_t) 0).). The rest of the bits are a counter. 54// 55// The 'value' field pthread_cond_t has the same layout. 56 57#define COND_SHARED_MASK 0x0001 58#define COND_CLOCK_MASK 0x0002 59#define COND_COUNTER_STEP 0x0004 60#define COND_FLAGS_MASK (COND_SHARED_MASK | COND_CLOCK_MASK) 61#define COND_COUNTER_MASK (~COND_FLAGS_MASK) 62 63#define COND_IS_SHARED(c) (((c) & COND_SHARED_MASK) != 0) 64#define COND_GET_CLOCK(c) (((c) & COND_CLOCK_MASK) >> 1) 65#define COND_SET_CLOCK(attr, c) ((attr) | (c << 1)) 66 67int pthread_condattr_init(pthread_condattr_t* attr) { 68 *attr = 0; 69 *attr |= PTHREAD_PROCESS_PRIVATE; 70 *attr |= (CLOCK_REALTIME << 1); 71 return 0; 72} 73 74int pthread_condattr_getpshared(const pthread_condattr_t* attr, int* pshared) { 75 *pshared = static_cast<int>(COND_IS_SHARED(*attr)); 76 return 0; 77} 78 79int pthread_condattr_setpshared(pthread_condattr_t* attr, int pshared) { 80 if (pshared != PTHREAD_PROCESS_SHARED && pshared != PTHREAD_PROCESS_PRIVATE) { 81 return EINVAL; 82 } 83 84 *attr |= pshared; 85 return 0; 86} 87 88int pthread_condattr_getclock(const pthread_condattr_t* attr, clockid_t* clock) { 89 *clock = COND_GET_CLOCK(*attr); 90 return 0; 91} 92 93int pthread_condattr_setclock(pthread_condattr_t* attr, clockid_t clock) { 94 if (clock != CLOCK_MONOTONIC && clock != CLOCK_REALTIME) { 95 return EINVAL; 96 } 97 98 *attr = COND_SET_CLOCK(*attr, clock); 99 return 0; 100} 101 102int pthread_condattr_destroy(pthread_condattr_t* attr) { 103 *attr = 0xdeada11d; 104 return 0; 105} 106 107struct pthread_cond_internal_t { 108 atomic_uint state; 109 110 bool process_shared() { 111 return COND_IS_SHARED(atomic_load_explicit(&state, memory_order_relaxed)); 112 } 113 114 int get_clock() { 115 return COND_GET_CLOCK(atomic_load_explicit(&state, memory_order_relaxed)); 116 } 117 118#if defined(__LP64__) 119 char __reserved[44]; 120#endif 121}; 122 123static pthread_cond_internal_t* __get_internal_cond(pthread_cond_t* cond_interface) { 124 static_assert(sizeof(pthread_cond_t) == sizeof(pthread_cond_internal_t), 125 "pthread_cond_t should actually be pthread_cond_internal_t in implementation."); 126 return reinterpret_cast<pthread_cond_internal_t*>(cond_interface); 127} 128 129int pthread_cond_init(pthread_cond_t* cond_interface, const pthread_condattr_t* attr) { 130 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 131 132 unsigned int init_state = 0; 133 if (attr != NULL) { 134 init_state = (*attr & COND_FLAGS_MASK); 135 } 136 atomic_init(&cond->state, init_state); 137 138 return 0; 139} 140 141int pthread_cond_destroy(pthread_cond_t* cond_interface) { 142 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 143 atomic_store_explicit(&cond->state, 0xdeadc04d, memory_order_relaxed); 144 return 0; 145} 146 147// This function is used by pthread_cond_broadcast and 148// pthread_cond_signal to atomically decrement the counter 149// then wake up thread_count threads. 150static int __pthread_cond_pulse(pthread_cond_internal_t* cond, int thread_count) { 151 // We don't use a release/seq_cst fence here. Because pthread_cond_wait/signal can't be 152 // used as a method for memory synchronization by itself. It should always be used with 153 // pthread mutexes. Note that Spurious wakeups from pthread_cond_wait/timedwait may occur, 154 // so when using condition variables there is always a boolean predicate involving shared 155 // variables associated with each condition wait that is true if the thread should proceed. 156 // If the predicate is seen true before a condition wait, pthread_cond_wait/timedwait will 157 // not be called. That's why pthread_wait/signal pair can't be used as a method for memory 158 // synchronization. And it doesn't help even if we use any fence here. 159 160 // The increase of value should leave flags alone, even if the value can overflows. 161 atomic_fetch_add_explicit(&cond->state, COND_COUNTER_STEP, memory_order_relaxed); 162 163 __futex_wake_ex(&cond->state, cond->process_shared(), thread_count); 164 return 0; 165} 166 167static int __pthread_cond_timedwait_relative(pthread_cond_internal_t* cond, pthread_mutex_t* mutex, 168 const timespec* rel_timeout_or_null) { 169 unsigned int old_state = atomic_load_explicit(&cond->state, memory_order_relaxed); 170 171 pthread_mutex_unlock(mutex); 172 int status = __futex_wait_ex(&cond->state, cond->process_shared(), old_state, rel_timeout_or_null); 173 pthread_mutex_lock(mutex); 174 175 if (status == -ETIMEDOUT) { 176 return ETIMEDOUT; 177 } 178 return 0; 179} 180 181static int __pthread_cond_timedwait(pthread_cond_internal_t* cond, pthread_mutex_t* mutex, 182 const timespec* abs_timeout_or_null, clockid_t clock) { 183 timespec ts; 184 timespec* rel_timeout = NULL; 185 186 if (abs_timeout_or_null != NULL) { 187 rel_timeout = &ts; 188 if (!timespec_from_absolute_timespec(*rel_timeout, *abs_timeout_or_null, clock)) { 189 return ETIMEDOUT; 190 } 191 } 192 193 return __pthread_cond_timedwait_relative(cond, mutex, rel_timeout); 194} 195 196int pthread_cond_broadcast(pthread_cond_t* cond_interface) { 197 return __pthread_cond_pulse(__get_internal_cond(cond_interface), INT_MAX); 198} 199 200int pthread_cond_signal(pthread_cond_t* cond_interface) { 201 return __pthread_cond_pulse(__get_internal_cond(cond_interface), 1); 202} 203 204int pthread_cond_wait(pthread_cond_t* cond_interface, pthread_mutex_t* mutex) { 205 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 206 return __pthread_cond_timedwait(cond, mutex, NULL, cond->get_clock()); 207} 208 209int pthread_cond_timedwait(pthread_cond_t *cond_interface, pthread_mutex_t * mutex, 210 const timespec *abstime) { 211 212 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 213 return __pthread_cond_timedwait(cond, mutex, abstime, cond->get_clock()); 214} 215 216#if !defined(__LP64__) 217// TODO: this exists only for backward binary compatibility on 32 bit platforms. 218extern "C" int pthread_cond_timedwait_monotonic(pthread_cond_t* cond_interface, 219 pthread_mutex_t* mutex, 220 const timespec* abs_timeout) { 221 222 return __pthread_cond_timedwait(__get_internal_cond(cond_interface), mutex, abs_timeout, 223 CLOCK_MONOTONIC); 224} 225 226extern "C" int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond_interface, 227 pthread_mutex_t* mutex, 228 const timespec* abs_timeout) { 229 return pthread_cond_timedwait_monotonic(cond_interface, mutex, abs_timeout); 230} 231 232extern "C" int pthread_cond_timedwait_relative_np(pthread_cond_t* cond_interface, 233 pthread_mutex_t* mutex, 234 const timespec* rel_timeout) { 235 236 return __pthread_cond_timedwait_relative(__get_internal_cond(cond_interface), mutex, rel_timeout); 237} 238 239extern "C" int pthread_cond_timeout_np(pthread_cond_t* cond_interface, 240 pthread_mutex_t* mutex, unsigned ms) { 241 timespec ts; 242 timespec_from_ms(ts, ms); 243 return pthread_cond_timedwait_relative_np(cond_interface, mutex, &ts); 244} 245#endif // !defined(__LP64__) 246