linuxthreads/mutex.c

   1 /* Linuxthreads - a simple clone()-based implementation of Posix        */
   2 /* threads for Linux.                                                   */
   3 /* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr)              */
   4 /*                                                                      */
   5 /* This program is free software; you can redistribute it and/or        */
   6 /* modify it under the terms of the GNU Library General Public License  */
   7 /* as published by the Free Software Foundation; either version 2       */
   8 /* of the License, or (at your option) any later version.               */
   9 /*                                                                      */
  10 /* This program is distributed in the hope that it will be useful,      */
  11 /* but WITHOUT ANY WARRANTY; without even the implied warranty of       */
  12 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        */
  13 /* GNU Library General Public License for more details.                 */
  14
  15 /* Mutexes */
  16
  17 #include <bits/libc-lock.h>
  18 #include <errno.h>
  19 #include <sched.h>
  20 #include <stddef.h>
  21 #include <limits.h>
  22 #include "pthread.h"
  23 #include "internals.h"
  24 #include "spinlock.h"
  25 #include "queue.h"
  26 #include "restart.h"
  27
  28 int __pthread_mutex_init(pthread_mutex_t * mutex,
  29                        const pthread_mutexattr_t * mutex_attr)
  30 {
  31   __pthread_init_lock(&mutex->__m_lock);
  32   mutex->__m_kind =
  33     mutex_attr == NULL ? PTHREAD_MUTEX_TIMED_NP : mutex_attr->__mutexkind;
  34   mutex->__m_count = 0;
  35   mutex->__m_owner = NULL;
  36   return 0;
  37 }
  38 strong_alias (__pthread_mutex_init, pthread_mutex_init)
  39
  40 int __pthread_mutex_destroy(pthread_mutex_t * mutex)
  41 {
  42   switch (mutex->__m_kind) {
  43   case PTHREAD_MUTEX_ADAPTIVE_NP:
  44   case PTHREAD_MUTEX_RECURSIVE_NP:
  45     if ((mutex->__m_lock.__status & 1) != 0)
  46       return EBUSY;
  47     return 0;
  48   case PTHREAD_MUTEX_ERRORCHECK_NP:
  49   case PTHREAD_MUTEX_TIMED_NP:
  50     if (mutex->__m_lock.__status != 0)
  51       return EBUSY;
  52     return 0;
  53   default:
  54     return EINVAL;
  55   }
  56 }
  57 strong_alias (__pthread_mutex_destroy, pthread_mutex_destroy)
  58
  59 int __pthread_mutex_trylock(pthread_mutex_t * mutex)
  60 {
  61   pthread_descr self;
  62   int retcode;
  63
  64   switch(mutex->__m_kind) {
  65   case PTHREAD_MUTEX_ADAPTIVE_NP:
  66     retcode = __pthread_trylock(&mutex->__m_lock);
  67     return retcode;
  68   case PTHREAD_MUTEX_RECURSIVE_NP:
  69     self = thread_self();
  70     if (mutex->__m_owner == self) {
  71       mutex->__m_count++;
  72       return 0;
  73     }
  74     retcode = __pthread_trylock(&mutex->__m_lock);
  75     if (retcode == 0) {
  76       mutex->__m_owner = self;
  77       mutex->__m_count = 0;
  78     }
  79     return retcode;
  80   case PTHREAD_MUTEX_ERRORCHECK_NP:
  81     retcode = __pthread_alt_trylock(&mutex->__m_lock);
  82     if (retcode == 0) {
  83       mutex->__m_owner = thread_self();
  84     }
  85     return retcode;
  86   case PTHREAD_MUTEX_TIMED_NP:
  87     retcode = __pthread_alt_trylock(&mutex->__m_lock);
  88     return retcode;
  89   default:
  90     return EINVAL;
  91   }
  92 }
  93 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
  94
  95 int __pthread_mutex_lock(pthread_mutex_t * mutex)
  96 {
  97   pthread_descr self;
  98
  99   switch(mutex->__m_kind) {
 100   case PTHREAD_MUTEX_ADAPTIVE_NP:
 101     __pthread_lock(&mutex->__m_lock, NULL);
 102     return 0;
 103   case PTHREAD_MUTEX_RECURSIVE_NP:
 104     self = thread_self();
 105     if (mutex->__m_owner == self) {
 106       mutex->__m_count++;
 107       return 0;
 108     }
 109     __pthread_lock(&mutex->__m_lock, self);
 110     mutex->__m_owner = self;
 111     mutex->__m_count = 0;
 112     return 0;
 113   case PTHREAD_MUTEX_ERRORCHECK_NP:
 114     self = thread_self();
 115     if (mutex->__m_owner == self) return EDEADLK;
 116     __pthread_alt_lock(&mutex->__m_lock, self);
 117     mutex->__m_owner = self;
 118     return 0;
 119   case PTHREAD_MUTEX_TIMED_NP:
 120     __pthread_alt_lock(&mutex->__m_lock, NULL);
 121     return 0;
 122   default:
 123     return EINVAL;
 124   }
 125 }
 126 strong_alias (__pthread_mutex_lock, pthread_mutex_lock)
 127
 128 int __pthread_mutex_timedlock (pthread_mutex_t *mutex,
 129                                const struct timespec *abstime)
 130 {
 131   pthread_descr self;
 132   int res;
 133
 134   if (__builtin_expect (abstime->tv_nsec, 0) < 0
 135       || __builtin_expect (abstime->tv_nsec, 0) >= 1000000000)
 136     return EINVAL;
 137
 138   switch(mutex->__m_kind) {
 139   case PTHREAD_MUTEX_ADAPTIVE_NP:
 140     __pthread_lock(&mutex->__m_lock, NULL);
 141     return 0;
 142   case PTHREAD_MUTEX_RECURSIVE_NP:
 143     self = thread_self();
 144     if (mutex->__m_owner == self) {
 145       mutex->__m_count++;
 146       return 0;
 147     }
 148     __pthread_lock(&mutex->__m_lock, self);
 149     mutex->__m_owner = self;
 150     mutex->__m_count = 0;
 151     return 0;
 152   case PTHREAD_MUTEX_ERRORCHECK_NP:
 153     self = thread_self();
 154     if (mutex->__m_owner == self) return EDEADLK;
 155     res = __pthread_alt_timedlock(&mutex->__m_lock, self, abstime);
 156     if (res != 0)
 157       {
 158         mutex->__m_owner = self;
 159         return 0;
 160       }
 161     return ETIMEDOUT;
 162   case PTHREAD_MUTEX_TIMED_NP:
 163     /* Only this type supports timed out lock. */
 164     return (__pthread_alt_timedlock(&mutex->__m_lock, NULL, abstime)
 165             ? 0 : ETIMEDOUT);
 166   default:
 167     return EINVAL;
 168   }
 169 }
 170 strong_alias (__pthread_mutex_timedlock, pthread_mutex_timedlock)
 171
 172 int __pthread_mutex_unlock(pthread_mutex_t * mutex)
 173 {
 174   switch (mutex->__m_kind) {
 175   case PTHREAD_MUTEX_ADAPTIVE_NP:
 176     __pthread_unlock(&mutex->__m_lock);
 177     return 0;
 178   case PTHREAD_MUTEX_RECURSIVE_NP:
 179     if (mutex->__m_owner != thread_self())
 180       return EPERM;
 181     if (mutex->__m_count > 0) {
 182       mutex->__m_count--;
 183       return 0;
 184     }
 185     mutex->__m_owner = NULL;
 186     __pthread_unlock(&mutex->__m_lock);
 187     return 0;
 188   case PTHREAD_MUTEX_ERRORCHECK_NP:
 189     if (mutex->__m_owner != thread_self() || mutex->__m_lock.__status == 0)
 190       return EPERM;
 191     mutex->__m_owner = NULL;
 192     __pthread_alt_unlock(&mutex->__m_lock);
 193     return 0;
 194   case PTHREAD_MUTEX_TIMED_NP:
 195     __pthread_alt_unlock(&mutex->__m_lock);
 196     return 0;
 197   default:
 198     return EINVAL;
 199   }
 200 }
 201 strong_alias (__pthread_mutex_unlock, pthread_mutex_unlock)
 202
 203 int __pthread_mutexattr_init(pthread_mutexattr_t *attr)
 204 {
 205   attr->__mutexkind = PTHREAD_MUTEX_TIMED_NP;
 206   return 0;
 207 }
 208 strong_alias (__pthread_mutexattr_init, pthread_mutexattr_init)
 209
 210 int __pthread_mutexattr_destroy(pthread_mutexattr_t *attr)
 211 {
 212   return 0;
 213 }
 214 strong_alias (__pthread_mutexattr_destroy, pthread_mutexattr_destroy)
 215
 216 int __pthread_mutexattr_settype(pthread_mutexattr_t *attr, int kind)
 217 {
 218   if (kind != PTHREAD_MUTEX_ADAPTIVE_NP
 219       && kind != PTHREAD_MUTEX_RECURSIVE_NP
 220       && kind != PTHREAD_MUTEX_ERRORCHECK_NP
 221       && kind != PTHREAD_MUTEX_TIMED_NP)
 222     return EINVAL;
 223   attr->__mutexkind = kind;
 224   return 0;
 225 }
 226 weak_alias (__pthread_mutexattr_settype, pthread_mutexattr_settype)
 227 strong_alias ( __pthread_mutexattr_settype, __pthread_mutexattr_setkind_np)
 228 weak_alias (__pthread_mutexattr_setkind_np, pthread_mutexattr_setkind_np)
 229
 230 int __pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *kind)
 231 {
 232   *kind = attr->__mutexkind;
 233   return 0;
 234 }
 235 weak_alias (__pthread_mutexattr_gettype, pthread_mutexattr_gettype)
 236 strong_alias (__pthread_mutexattr_gettype, __pthread_mutexattr_getkind_np)
 237 weak_alias (__pthread_mutexattr_getkind_np, pthread_mutexattr_getkind_np)
 238
 239 int __pthread_mutexattr_getpshared (const pthread_mutexattr_t *attr,
 240                                    int *pshared)
 241 {
 242   *pshared = PTHREAD_PROCESS_PRIVATE;
 243   return 0;
 244 }
 245 weak_alias (__pthread_mutexattr_getpshared, pthread_mutexattr_getpshared)
 246
 247 int __pthread_mutexattr_setpshared (pthread_mutexattr_t *attr, int pshared)
 248 {
 249   if (pshared != PTHREAD_PROCESS_PRIVATE && pshared != PTHREAD_PROCESS_SHARED)
 250     return EINVAL;
 251
 252   /* For now it is not possible to shared a conditional variable.  */
 253   if (pshared != PTHREAD_PROCESS_PRIVATE)
 254     return ENOSYS;
 255
 256   return 0;
 257 }
 258 weak_alias (__pthread_mutexattr_setpshared, pthread_mutexattr_setpshared)
 259
 260 /* Once-only execution */
 261
 262 static pthread_mutex_t once_masterlock = PTHREAD_MUTEX_INITIALIZER;
 263 static pthread_cond_t once_finished = PTHREAD_COND_INITIALIZER;
 264 static int fork_generation = 0; /* Child process increments this after fork. */
 265
 266 enum { NEVER = 0, IN_PROGRESS = 1, DONE = 2 };
 267
 268 /* If a thread is canceled while calling the init_routine out of
 269    pthread once, this handler will reset the once_control variable
 270    to the NEVER state. */
 271
 272 static void pthread_once_cancelhandler(void *arg)
 273 {
 274     pthread_once_t *once_control = arg;
 275
 276     pthread_mutex_lock(&once_masterlock);
 277     *once_control = NEVER;
 278     pthread_mutex_unlock(&once_masterlock);
 279     pthread_cond_broadcast(&once_finished);
 280 }
 281
 282 int __pthread_once(pthread_once_t * once_control, void (*init_routine)(void))
 283 {
 284   /* flag for doing the condition broadcast outside of mutex */
 285   int state_changed;
 286
 287   /* Test without locking first for speed */
 288   if (*once_control == DONE) {
 289     READ_MEMORY_BARRIER();
 290     return 0;
 291   }
 292   /* Lock and test again */
 293
 294   state_changed = 0;
 295
 296   pthread_mutex_lock(&once_masterlock);
 297
 298   /* If this object was left in an IN_PROGRESS state in a parent
 299      process (indicated by stale generation field), reset it to NEVER. */
 300   if ((*once_control & 3) == IN_PROGRESS && (*once_control & ~3) != fork_generation)
 301     *once_control = NEVER;
 302
 303   /* If init_routine is being called from another routine, wait until
 304      it completes. */
 305   while ((*once_control & 3) == IN_PROGRESS) {
 306     pthread_cond_wait(&once_finished, &once_masterlock);
 307   }
 308   /* Here *once_control is stable and either NEVER or DONE. */
 309   if (*once_control == NEVER) {
 310     *once_control = IN_PROGRESS | fork_generation;
 311     pthread_mutex_unlock(&once_masterlock);
 312     pthread_cleanup_push(pthread_once_cancelhandler, once_control);
 313     init_routine();
 314     pthread_cleanup_pop(0);
 315     pthread_mutex_lock(&once_masterlock);
 316     WRITE_MEMORY_BARRIER();
 317     *once_control = DONE;
 318     state_changed = 1;
 319   }
 320   pthread_mutex_unlock(&once_masterlock);
 321
 322   if (state_changed)
 323     pthread_cond_broadcast(&once_finished);
 324
 325   return 0;
 326 }
 327 strong_alias (__pthread_once, pthread_once)
 328
 329 /*
 330  * Handle the state of the pthread_once mechanism across forks.  The
 331  * once_masterlock is acquired in the parent process prior to a fork to ensure
 332  * that no thread is in the critical region protected by the lock.  After the
 333  * fork, the lock is released. In the child, the lock and the condition
 334  * variable are simply reset.  The child also increments its generation
 335  * counter which lets pthread_once calls detect stale IN_PROGRESS states
 336  * and reset them back to NEVER.
 337  */
 338
 339 void __pthread_once_fork_prepare(void)
 340 {
 341   pthread_mutex_lock(&once_masterlock);
 342 }
 343
 344 void __pthread_once_fork_parent(void)
 345 {
 346   pthread_mutex_unlock(&once_masterlock);
 347 }
 348
 349 void __pthread_once_fork_child(void)
 350 {
 351   pthread_mutex_init(&once_masterlock, NULL);
 352   pthread_cond_init(&once_finished, NULL);
 353   if (fork_generation <= INT_MAX - 4)
 354     fork_generation += 4;       /* leave least significant two bits zero */
 355   else
 356     fork_generation = 0;
 357 }