1 /* $NetBSD: pthread_mutex.c,v 1.16 2003/05/27 15:22:56 christos Exp $ */ 2 3 /*- 4 * Copyright (c) 2001, 2003 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Nathan J. Williams, and by Jason R. Thorpe. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39 #include <sys/cdefs.h> 40 __RCSID("$NetBSD: pthread_mutex.c,v 1.16 2003/05/27 15:22:56 christos Exp $"); 41 42 #include <errno.h> 43 #include <limits.h> 44 #include <stdlib.h> 45 #include <string.h> 46 47 #include "pthread.h" 48 #include "pthread_int.h" 49 50 static int pthread_mutex_lock_slow(pthread_mutex_t *); 51 52 __strong_alias(__libc_mutex_init,pthread_mutex_init) 53 __strong_alias(__libc_mutex_lock,pthread_mutex_lock) 54 __strong_alias(__libc_mutex_trylock,pthread_mutex_trylock) 55 __strong_alias(__libc_mutex_unlock,pthread_mutex_unlock) 56 __strong_alias(__libc_mutex_destroy,pthread_mutex_destroy) 57 58 __strong_alias(__libc_mutexattr_init,pthread_mutexattr_init) 59 __strong_alias(__libc_mutexattr_destroy,pthread_mutexattr_destroy) 60 __strong_alias(__libc_mutexattr_settype,pthread_mutexattr_settype) 61 62 __strong_alias(__libc_thr_once,pthread_once) 63 64 struct mutex_private { 65 int type; 66 int recursecount; 67 }; 68 69 static const struct mutex_private mutex_private_default = { 70 PTHREAD_MUTEX_DEFAULT, 71 0, 72 }; 73 74 struct mutexattr_private { 75 int type; 76 }; 77 78 static const struct mutexattr_private mutexattr_private_default = { 79 PTHREAD_MUTEX_DEFAULT, 80 }; 81 82 /* 83 * If the mutex does not already have private data (i.e. was statically 84 * initialized), then give it the default. 85 */ 86 #define GET_MUTEX_PRIVATE(mutex, mp) \ 87 do { \ 88 if (__predict_false((mp = (mutex)->ptm_private) == NULL)) { \ 89 /* LINTED cast away const */ \ 90 mp = ((mutex)->ptm_private = \ 91 (void *)&mutex_private_default); \ 92 } \ 93 } while (/*CONSTCOND*/0) 94 95 int 96 pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *attr) 97 { 98 struct mutexattr_private *map; 99 struct mutex_private *mp; 100 101 pthread__error(EINVAL, "Invalid mutex attribute", 102 (attr == NULL) || (attr->ptma_magic == _PT_MUTEXATTR_MAGIC)); 103 104 if (attr != NULL && (map = attr->ptma_private) != NULL && 105 memcmp(map, &mutexattr_private_default, sizeof(*map)) != 0) { 106 mp = malloc(sizeof(*mp)); 107 if (mp == NULL) 108 return ENOMEM; 109 110 mp->type = map->type; 111 mp->recursecount = 0; 112 } else { 113 /* LINTED cast away const */ 114 mp = (struct mutex_private *) &mutex_private_default; 115 } 116 117 mutex->ptm_magic = _PT_MUTEX_MAGIC; 118 mutex->ptm_owner = NULL; 119 pthread_lockinit(&mutex->ptm_lock); 120 pthread_lockinit(&mutex->ptm_interlock); 121 PTQ_INIT(&mutex->ptm_blocked); 122 mutex->ptm_private = mp; 123 124 return 0; 125 } 126 127 128 int 129 pthread_mutex_destroy(pthread_mutex_t *mutex) 130 { 131 132 pthread__error(EINVAL, "Invalid mutex", 133 mutex->ptm_magic == _PT_MUTEX_MAGIC); 134 pthread__error(EBUSY, "Destroying locked mutex", 135 mutex->ptm_lock == __SIMPLELOCK_UNLOCKED); 136 137 mutex->ptm_magic = _PT_MUTEX_DEAD; 138 if (mutex->ptm_private != NULL && 139 mutex->ptm_private != (const void *)&mutex_private_default) 140 free(mutex->ptm_private); 141 142 return 0; 143 } 144 145 146 /* 147 * Note regarding memory visibility: Pthreads has rules about memory 148 * visibility and mutexes. Very roughly: Memory a thread can see when 149 * it unlocks a mutex can be seen by another thread that locks the 150 * same mutex. 151 * 152 * A memory barrier after a lock and before an unlock will provide 153 * this behavior. This code relies on pthread__simple_lock_try() to issue 154 * a barrier after obtaining a lock, and on pthread__simple_unlock() to 155 * issue a barrier before releasing a lock. 156 */ 157 158 int 159 pthread_mutex_lock(pthread_mutex_t *mutex) 160 { 161 int error; 162 163 PTHREADD_ADD(PTHREADD_MUTEX_LOCK); 164 /* 165 * Note that if we get the lock, we don't have to deal with any 166 * non-default lock type handling. 167 */ 168 if (__predict_false(pthread__simple_lock_try(&mutex->ptm_lock) == 0)) { 169 error = pthread_mutex_lock_slow(mutex); 170 if (error) 171 return error; 172 } 173 174 /* We have the lock! */ 175 /* 176 * Identifying ourselves may be slow, and this assignment is 177 * only needed for (a) debugging identity of the owning thread 178 * and (b) handling errorcheck and recursive mutexes. It's 179 * better to just stash our stack pointer here and let those 180 * slow exception cases compute the stack->thread mapping. 181 */ 182 mutex->ptm_owner = (pthread_t)pthread__sp(); 183 184 return 0; 185 } 186 187 188 static int 189 pthread_mutex_lock_slow(pthread_mutex_t *mutex) 190 { 191 pthread_t self; 192 193 pthread__error(EINVAL, "Invalid mutex", 194 mutex->ptm_magic == _PT_MUTEX_MAGIC); 195 196 self = pthread__self(); 197 198 PTHREADD_ADD(PTHREADD_MUTEX_LOCK_SLOW); 199 while (/*CONSTCOND*/1) { 200 if (pthread__simple_lock_try(&mutex->ptm_lock)) 201 break; /* got it! */ 202 203 /* Okay, didn't look free. Get the interlock... */ 204 pthread_spinlock(self, &mutex->ptm_interlock); 205 /* 206 * The mutex_unlock routine will get the interlock 207 * before looking at the list of sleepers, so if the 208 * lock is held we can safely put ourselves on the 209 * sleep queue. If it's not held, we can try taking it 210 * again. 211 */ 212 if (mutex->ptm_lock == __SIMPLELOCK_LOCKED) { 213 struct mutex_private *mp; 214 215 GET_MUTEX_PRIVATE(mutex, mp); 216 217 if (pthread__id(mutex->ptm_owner) == self) { 218 switch (mp->type) { 219 case PTHREAD_MUTEX_ERRORCHECK: 220 pthread_spinunlock(self, 221 &mutex->ptm_interlock); 222 return EDEADLK; 223 224 case PTHREAD_MUTEX_RECURSIVE: 225 /* 226 * It's safe to do this without 227 * holding the interlock, because 228 * we only modify it if we know we 229 * own the mutex. 230 */ 231 pthread_spinunlock(self, 232 &mutex->ptm_interlock); 233 if (mp->recursecount == INT_MAX) 234 return EAGAIN; 235 mp->recursecount++; 236 return 0; 237 } 238 } 239 240 PTQ_INSERT_HEAD(&mutex->ptm_blocked, self, pt_sleep); 241 /* 242 * Locking a mutex is not a cancellation 243 * point, so we don't need to do the 244 * test-cancellation dance. We may get woken 245 * up spuriously by pthread_cancel or signals, 246 * but it's okay since we're just going to 247 * retry. 248 */ 249 pthread_spinlock(self, &self->pt_statelock); 250 self->pt_state = PT_STATE_BLOCKED_QUEUE; 251 self->pt_sleepobj = mutex; 252 self->pt_sleepq = &mutex->ptm_blocked; 253 self->pt_sleeplock = &mutex->ptm_interlock; 254 pthread_spinunlock(self, &self->pt_statelock); 255 256 pthread__block(self, &mutex->ptm_interlock); 257 /* interlock is not held when we return */ 258 } else { 259 pthread_spinunlock(self, &mutex->ptm_interlock); 260 } 261 /* Go around for another try. */ 262 } 263 264 return 0; 265 } 266 267 268 int 269 pthread_mutex_trylock(pthread_mutex_t *mutex) 270 { 271 272 pthread__error(EINVAL, "Invalid mutex", 273 mutex->ptm_magic == _PT_MUTEX_MAGIC); 274 275 PTHREADD_ADD(PTHREADD_MUTEX_TRYLOCK); 276 if (pthread__simple_lock_try(&mutex->ptm_lock) == 0) { 277 struct mutex_private *mp; 278 279 GET_MUTEX_PRIVATE(mutex, mp); 280 281 /* 282 * These tests can be performed without holding the 283 * interlock because these fields are only modified 284 * if we know we own the mutex. 285 */ 286 if ((mp->type == PTHREAD_MUTEX_RECURSIVE) && 287 (pthread__id(mutex->ptm_owner) == pthread__self())) { 288 if (mp->recursecount == INT_MAX) 289 return EAGAIN; 290 mp->recursecount++; 291 return 0; 292 } 293 294 return EBUSY; 295 } 296 297 /* see comment at the end of pthread_mutex_lock() */ 298 mutex->ptm_owner = (pthread_t)pthread__sp(); 299 300 return 0; 301 } 302 303 304 int 305 pthread_mutex_unlock(pthread_mutex_t *mutex) 306 { 307 struct mutex_private *mp; 308 pthread_t self, blocked; 309 int weown; 310 311 pthread__error(EINVAL, "Invalid mutex", 312 mutex->ptm_magic == _PT_MUTEX_MAGIC); 313 314 PTHREADD_ADD(PTHREADD_MUTEX_UNLOCK); 315 316 GET_MUTEX_PRIVATE(mutex, mp); 317 318 /* 319 * These tests can be performed without holding the 320 * interlock because these fields are only modified 321 * if we know we own the mutex. 322 */ 323 weown = (pthread__id(mutex->ptm_owner) == pthread__self()); 324 switch (mp->type) { 325 case PTHREAD_MUTEX_RECURSIVE: 326 if (!weown) 327 return EPERM; 328 if (mp->recursecount != 0) { 329 mp->recursecount--; 330 return 0; 331 } 332 break; 333 case PTHREAD_MUTEX_ERRORCHECK: 334 if (!weown) 335 return EPERM; 336 /*FALLTHROUGH*/ 337 default: 338 if (__predict_false(!weown)) { 339 pthread__error(EPERM, "Unlocking unlocked mutex", 340 (mutex->ptm_owner != 0)); 341 pthread__error(EPERM, 342 "Unlocking mutex owned by another thread", weown); 343 } 344 break; 345 } 346 347 mutex->ptm_owner = NULL; 348 pthread__simple_unlock(&mutex->ptm_lock); 349 /* 350 * Do a double-checked locking dance to see if there are any 351 * waiters. If we don't see any waiters, we can exit, because 352 * we've already released the lock. If we do see waiters, they 353 * were probably waiting on us... there's a slight chance that 354 * they are waiting on a different thread's ownership of the 355 * lock that happened between the unlock above and this 356 * examination of the queue; if so, no harm is done, as the 357 * waiter will loop and see that the mutex is still locked. 358 */ 359 if (!PTQ_EMPTY(&mutex->ptm_blocked)) { 360 self = pthread__self(); 361 pthread_spinlock(self, &mutex->ptm_interlock); 362 blocked = PTQ_FIRST(&mutex->ptm_blocked); 363 if (blocked) 364 PTQ_REMOVE(&mutex->ptm_blocked, blocked, pt_sleep); 365 pthread_spinunlock(self, &mutex->ptm_interlock); 366 367 /* Give the head of the blocked queue another try. */ 368 if (blocked) { 369 PTHREADD_ADD(PTHREADD_MUTEX_UNLOCK_UNBLOCK); 370 pthread__sched(self, blocked); 371 } 372 } 373 return 0; 374 } 375 376 int 377 pthread_mutexattr_init(pthread_mutexattr_t *attr) 378 { 379 struct mutexattr_private *map; 380 381 map = malloc(sizeof(*map)); 382 if (map == NULL) 383 return ENOMEM; 384 385 *map = mutexattr_private_default; 386 387 attr->ptma_magic = _PT_MUTEXATTR_MAGIC; 388 attr->ptma_private = map; 389 390 return 0; 391 } 392 393 394 int 395 pthread_mutexattr_destroy(pthread_mutexattr_t *attr) 396 { 397 398 pthread__error(EINVAL, "Invalid mutex attribute", 399 attr->ptma_magic == _PT_MUTEXATTR_MAGIC); 400 401 attr->ptma_magic = _PT_MUTEXATTR_DEAD; 402 if (attr->ptma_private != NULL) 403 free(attr->ptma_private); 404 405 return 0; 406 } 407 408 409 int 410 pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *typep) 411 { 412 struct mutexattr_private *map; 413 414 pthread__error(EINVAL, "Invalid mutex attribute", 415 attr->ptma_magic == _PT_MUTEXATTR_MAGIC); 416 417 map = attr->ptma_private; 418 419 *typep = map->type; 420 421 return 0; 422 } 423 424 425 int 426 pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type) 427 { 428 struct mutexattr_private *map; 429 430 pthread__error(EINVAL, "Invalid mutex attribute", 431 attr->ptma_magic == _PT_MUTEXATTR_MAGIC); 432 433 map = attr->ptma_private; 434 435 switch (type) { 436 case PTHREAD_MUTEX_NORMAL: 437 case PTHREAD_MUTEX_ERRORCHECK: 438 case PTHREAD_MUTEX_RECURSIVE: 439 map->type = type; 440 break; 441 442 default: 443 return EINVAL; 444 } 445 446 return 0; 447 } 448 449 450 int 451 pthread_once(pthread_once_t *once_control, void (*routine)(void)) 452 { 453 454 if (once_control->pto_done == 0) { 455 pthread_mutex_lock(&once_control->pto_mutex); 456 if (once_control->pto_done == 0) { 457 routine(); 458 once_control->pto_done = 1; 459 } 460 pthread_mutex_unlock(&once_control->pto_mutex); 461 } 462 463 return 0; 464 } 465