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 0 and 53 // CLOCK_MONOTONIC is 1). The rest of the bits are a counter. 54 // 55 // The 'value' field in 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 67 int 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 74 int pthread_condattr_getpshared(const pthread_condattr_t* attr, int* pshared) { 75 *pshared = static_cast<int>(COND_IS_SHARED(*attr)); 76 return 0; 77 } 78 79 int 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 88 int pthread_condattr_getclock(const pthread_condattr_t* attr, clockid_t* clock) { 89 *clock = COND_GET_CLOCK(*attr); 90 return 0; 91 } 92 93 int 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 } 101 102 int pthread_condattr_destroy(pthread_condattr_t* attr) { 103 *attr = 0xdeada11d; 104 return 0; 105 } 106 107 struct 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 bool use_realtime_clock() { 115 return COND_GET_CLOCK(atomic_load_explicit(&state, memory_order_relaxed)) == CLOCK_REALTIME; 116 } 117 118 #if defined(__LP64__) 119 char __reserved[44]; 120 #endif 121 }; 122 123 static_assert(sizeof(pthread_cond_t) == sizeof(pthread_cond_internal_t), 124 "pthread_cond_t should actually be pthread_cond_internal_t in implementation."); 125 126 // For binary compatibility with old version of pthread_cond_t, we can't use more strict alignment 127 // than 4-byte alignment. 128 static_assert(alignof(pthread_cond_t) == 4, 129 "pthread_cond_t should fulfill the alignment requirement of pthread_cond_internal_t."); 130 131 static pthread_cond_internal_t* __get_internal_cond(pthread_cond_t* cond_interface) { 132 return reinterpret_cast<pthread_cond_internal_t*>(cond_interface); 133 } 134 135 int pthread_cond_init(pthread_cond_t* cond_interface, const pthread_condattr_t* attr) { 136 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 137 138 unsigned int init_state = 0; 139 if (attr != nullptr) { 140 init_state = (*attr & COND_FLAGS_MASK); 141 } 142 atomic_init(&cond->state, init_state); 143 144 return 0; 145 } 146 147 int pthread_cond_destroy(pthread_cond_t* cond_interface) { 148 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 149 atomic_store_explicit(&cond->state, 0xdeadc04d, memory_order_relaxed); 150 return 0; 151 } 152 153 // This function is used by pthread_cond_broadcast and 154 // pthread_cond_signal to atomically decrement the counter 155 // then wake up thread_count threads. 156 static int __pthread_cond_pulse(pthread_cond_internal_t* cond, int thread_count) { 157 // We don't use a release/seq_cst fence here. Because pthread_cond_wait/signal can't be 158 // used as a method for memory synchronization by itself. It should always be used with 159 // pthread mutexes. Note that Spurious wakeups from pthread_cond_wait/timedwait may occur, 160 // so when using condition variables there is always a boolean predicate involving shared 161 // variables associated with each condition wait that is true if the thread should proceed. 162 // If the predicate is seen true before a condition wait, pthread_cond_wait/timedwait will 163 // not be called. That's why pthread_wait/signal pair can't be used as a method for memory 164 // synchronization. And it doesn't help even if we use any fence here. 165 166 // The increase of value should leave flags alone, even if the value can overflows. 167 atomic_fetch_add_explicit(&cond->state, COND_COUNTER_STEP, memory_order_relaxed); 168 169 __futex_wake_ex(&cond->state, cond->process_shared(), thread_count); 170 return 0; 171 } 172 173 static int __pthread_cond_timedwait(pthread_cond_internal_t* cond, pthread_mutex_t* mutex, 174 bool use_realtime_clock, const timespec* abs_timeout_or_null) { 175 int result = check_timespec(abs_timeout_or_null, true); 176 if (result != 0) { 177 return result; 178 } 179 180 unsigned int old_state = atomic_load_explicit(&cond->state, memory_order_relaxed); 181 pthread_mutex_unlock(mutex); 182 int status = __futex_wait_ex(&cond->state, cond->process_shared(), old_state, 183 use_realtime_clock, abs_timeout_or_null); 184 pthread_mutex_lock(mutex); 185 186 if (status == -ETIMEDOUT) { 187 return ETIMEDOUT; 188 } 189 return 0; 190 } 191 192 int pthread_cond_broadcast(pthread_cond_t* cond_interface) { 193 return __pthread_cond_pulse(__get_internal_cond(cond_interface), INT_MAX); 194 } 195 196 int pthread_cond_signal(pthread_cond_t* cond_interface) { 197 return __pthread_cond_pulse(__get_internal_cond(cond_interface), 1); 198 } 199 200 int pthread_cond_wait(pthread_cond_t* cond_interface, pthread_mutex_t* mutex) { 201 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 202 return __pthread_cond_timedwait(cond, mutex, false, nullptr); 203 } 204 205 int pthread_cond_timedwait(pthread_cond_t *cond_interface, pthread_mutex_t * mutex, 206 const timespec *abstime) { 207 208 pthread_cond_internal_t* cond = __get_internal_cond(cond_interface); 209 return __pthread_cond_timedwait(cond, mutex, cond->use_realtime_clock(), abstime); 210 } 211 212 extern "C" int pthread_cond_timedwait_monotonic_np(pthread_cond_t* cond_interface, 213 pthread_mutex_t* mutex, 214 const timespec* abs_timeout) { 215 return __pthread_cond_timedwait(__get_internal_cond(cond_interface), mutex, false, abs_timeout); 216 } 217 218 #if !defined(__LP64__) 219 // TODO: this exists only for backward binary compatibility on 32 bit platforms. 220 extern "C" int pthread_cond_timedwait_monotonic(pthread_cond_t* cond_interface, 221 pthread_mutex_t* mutex, 222 const timespec* abs_timeout) { 223 return pthread_cond_timedwait_monotonic_np(cond_interface, mutex, abs_timeout); 224 } 225 226 // Force this function using CLOCK_MONOTONIC because it was always using 227 // CLOCK_MONOTONIC in history. 228 extern "C" int pthread_cond_timedwait_relative_np(pthread_cond_t* cond_interface, 229 pthread_mutex_t* mutex, 230 const timespec* rel_timeout) { 231 timespec ts; 232 timespec* abs_timeout = nullptr; 233 if (rel_timeout != nullptr) { 234 absolute_timespec_from_timespec(ts, *rel_timeout, CLOCK_MONOTONIC); 235 abs_timeout = &ts; 236 } 237 return __pthread_cond_timedwait(__get_internal_cond(cond_interface), mutex, false, abs_timeout); 238 } 239 240 extern "C" int pthread_cond_timeout_np(pthread_cond_t* cond_interface, 241 pthread_mutex_t* mutex, unsigned ms) { 242 timespec ts; 243 timespec_from_ms(ts, ms); 244 return pthread_cond_timedwait_relative_np(cond_interface, mutex, &ts); 245 } 246 #endif // !defined(__LP64__) 247
