libpthread/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 <errno.h>
  18 #include <sched.h>
  19 #include <stddef.h>
  20 #include <limits.h>
  21 #include "pthread.h"
  22 #include "internals.h"
  23 #include "spinlock.h"
  24 #include "queue.h"
  25 #include "restart.h"
  26
  27 int attribute_hidden __pthread_mutex_init(pthread_mutex_t * mutex,
  28                        const pthread_mutexattr_t * mutex_attr)
  29 {
  30   __pthread_init_lock(&mutex->__m_lock);
  31   mutex->__m_kind =
  32     mutex_attr == NULL ? PTHREAD_MUTEX_TIMED_NP : mutex_attr->__mutexkind;
  33   mutex->__m_count = 0;
  34   mutex->__m_owner = NULL;
  35   return 0;
  36 }
  37 strong_alias (__pthread_mutex_init, pthread_mutex_init)
  38
  39 int attribute_hidden __pthread_mutex_destroy(pthread_mutex_t * mutex)
  40 {
  41   switch (mutex->__m_kind) {
  42   case PTHREAD_MUTEX_ADAPTIVE_NP:
  43   case PTHREAD_MUTEX_RECURSIVE_NP:
  44     if ((mutex->__m_lock.__status & 1) != 0)
  45       return EBUSY;
  46     return 0;
  47   case PTHREAD_MUTEX_ERRORCHECK_NP:
  48   case PTHREAD_MUTEX_TIMED_NP:
  49     if (mutex->__m_lock.__status != 0)
  50       return EBUSY;
  51     return 0;
  52   default:
  53     return EINVAL;
  54   }
  55 }
  56 strong_alias (__pthread_mutex_destroy, pthread_mutex_destroy)
  57
  58 int attribute_hidden __pthread_mutex_trylock(pthread_mutex_t * mutex)
  59 {
  60   pthread_descr self;
  61   int retcode;
  62
  63   switch(mutex->__m_kind) {
  64   case PTHREAD_MUTEX_ADAPTIVE_NP:
  65     retcode = __pthread_trylock(&mutex->__m_lock);
  66     return retcode;
  67   case PTHREAD_MUTEX_RECURSIVE_NP:
  68     self = thread_self();
  69     if (mutex->__m_owner == self) {
  70       mutex->__m_count++;
  71       return 0;
  72     }
  73     retcode = __pthread_trylock(&mutex->__m_lock);
  74     if (retcode == 0) {
  75       mutex->__m_owner = self;
  76       mutex->__m_count = 0;
  77     }
  78     return retcode;
  79   case PTHREAD_MUTEX_ERRORCHECK_NP:
  80     retcode = __pthread_alt_trylock(&mutex->__m_lock);
  81     if (retcode == 0) {
  82       mutex->__m_owner = thread_self();
  83     }
  84     return retcode;
  85   case PTHREAD_MUTEX_TIMED_NP:
  86     retcode = __pthread_alt_trylock(&mutex->__m_lock);
  87     return retcode;
  88   default:
  89     return EINVAL;
  90   }
  91 }
  92 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
  93
  94 int attribute_hidden __pthread_mutex_lock(pthread_mutex_t * mutex)
  95 {
  96   pthread_descr self;
  97
  98   switch(mutex->__m_kind) {
  99   case PTHREAD_MUTEX_ADAPTIVE_NP:
 100     __pthread_lock(&mutex->__m_lock, NULL);
 101     return 0;
 102   case PTHREAD_MUTEX_RECURSIVE_NP:
 103     self = thread_self();
 104     if (mutex->__m_owner == self) {
 105       mutex->__m_count++;
 106       return 0;
 107     }
 108     __pthread_lock(&mutex->__m_lock, self);
 109     mutex->__m_owner = self;
 110     mutex->__m_count = 0;
 111     return 0;
 112   case PTHREAD_MUTEX_ERRORCHECK_NP:
 113     self = thread_self();
 114     if (mutex->__m_owner == self) return EDEADLK;
 115     __pthread_alt_lock(&mutex->__m_lock, self);
 116     mutex->__m_owner = self;
 117     return 0;
 118   case PTHREAD_MUTEX_TIMED_NP:
 119     __pthread_alt_lock(&mutex->__m_lock, NULL);
 120     return 0;
 121   default:
 122     return EINVAL;
 123   }
 124 }
 125 strong_alias (__pthread_mutex_lock, pthread_mutex_lock)
 126
 127 int pthread_mutex_timedlock (pthread_mutex_t *mutex,
 128                                const struct timespec *abstime)
 129 {
 130   pthread_descr self;
 131   int res;
 132
 133   if (__builtin_expect (abstime->tv_nsec, 0) < 0
 134       || __builtin_expect (abstime->tv_nsec, 0) >= 1000000000)
 135     return EINVAL;
 136
 137   switch(mutex->__m_kind) {
 138   case PTHREAD_MUTEX_ADAPTIVE_NP:
 139     __pthread_lock(&mutex->__m_lock, NULL);
 140     return 0;
 141   case PTHREAD_MUTEX_RECURSIVE_NP:
 142     self = thread_self();
 143     if (mutex->__m_owner == self) {
 144       mutex->__m_count++;
 145       return 0;
 146     }
 147     __pthread_lock(&mutex->__m_lock, self);
 148     mutex->__m_owner = self;
 149     mutex->__m_count = 0;
 150     return 0;
 151   case PTHREAD_MUTEX_ERRORCHECK_NP:
 152     self = thread_self();
 153     if (mutex->__m_owner == self) return EDEADLK;
 154     res = __pthread_alt_timedlock(&mutex->__m_lock, self, abstime);
 155     if (res != 0)
 156       {
 157         mutex->__m_owner = self;
 158         return 0;
 159       }
 160     return ETIMEDOUT;
 161   case PTHREAD_MUTEX_TIMED_NP:
 162     /* Only this type supports timed out lock. */
 163     return (__pthread_alt_timedlock(&mutex->__m_lock, NULL, abstime)
 164             ? 0 : ETIMEDOUT);
 165   default:
 166     return EINVAL;
 167   }
 168 }
 169
 170 int attribute_hidden __pthread_mutex_unlock(pthread_mutex_t * mutex)
 171 {
 172   switch (mutex->__m_kind) {
 173   case PTHREAD_MUTEX_ADAPTIVE_NP:
 174     __pthread_unlock(&mutex->__m_lock);
 175     return 0;
 176   case PTHREAD_MUTEX_RECURSIVE_NP:
 177     if (mutex->__m_owner != thread_self())
 178       return EPERM;
 179     if (mutex->__m_count > 0) {
 180       mutex->__m_count--;
 181       return 0;
 182     }
 183     mutex->__m_owner = NULL;
 184     __pthread_unlock(&mutex->__m_lock);
 185     return 0;
 186   case PTHREAD_MUTEX_ERRORCHECK_NP:
 187     if (mutex->__m_owner != thread_self() || mutex->__m_lock.__status == 0)
 188       return EPERM;
 189     mutex->__m_owner = NULL;
 190     __pthread_alt_unlock(&mutex->__m_lock);
 191     return 0;
 192   case PTHREAD_MUTEX_TIMED_NP:
 193     __pthread_alt_unlock(&mutex->__m_lock);
 194     return 0;
 195   default:
 196     return EINVAL;
 197   }
 198 }
 199 strong_alias (__pthread_mutex_unlock, pthread_mutex_unlock)
 200
 201 int attribute_hidden __pthread_mutexattr_init(pthread_mutexattr_t *attr)
 202 {
 203   attr->__mutexkind = PTHREAD_MUTEX_TIMED_NP;
 204   return 0;
 205 }
 206 strong_alias(__pthread_mutexattr_init,pthread_mutexattr_init)
 207
 208 int attribute_hidden __pthread_mutexattr_destroy(pthread_mutexattr_t *attr attribute_unused)
 209 {
 210   return 0;
 211 }
 212 strong_alias(__pthread_mutexattr_destroy,pthread_mutexattr_destroy)
 213
 214 int attribute_hidden __pthread_mutexattr_settype(pthread_mutexattr_t *attr, int kind)
 215 {
 216   if (kind != PTHREAD_MUTEX_ADAPTIVE_NP
 217       && kind != PTHREAD_MUTEX_RECURSIVE_NP
 218       && kind != PTHREAD_MUTEX_ERRORCHECK_NP
 219       && kind != PTHREAD_MUTEX_TIMED_NP)
 220     return EINVAL;
 221   attr->__mutexkind = kind;
 222   return 0;
 223 }
 224 strong_alias(__pthread_mutexattr_settype,pthread_mutexattr_settype)
 225 strong_alias (__pthread_mutexattr_settype, __pthread_mutexattr_setkind_np)
 226 weak_alias (__pthread_mutexattr_setkind_np, pthread_mutexattr_setkind_np)
 227
 228 int __pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *kind) attribute_hidden;
 229 int __pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *kind)
 230 {
 231   *kind = attr->__mutexkind;
 232   return 0;
 233 }
 234 weak_alias (__pthread_mutexattr_gettype, pthread_mutexattr_gettype)
 235 strong_alias (__pthread_mutexattr_gettype, __pthread_mutexattr_getkind_np)
 236 weak_alias (__pthread_mutexattr_getkind_np, pthread_mutexattr_getkind_np)
 237
 238 int __pthread_mutexattr_getpshared (const pthread_mutexattr_t *attr attribute_unused,
 239                                    int *pshared) attribute_hidden;
 240 int __pthread_mutexattr_getpshared (const pthread_mutexattr_t *attr attribute_unused,
 241                                    int *pshared)
 242 {
 243   *pshared = PTHREAD_PROCESS_PRIVATE;
 244   return 0;
 245 }
 246 weak_alias (__pthread_mutexattr_getpshared, pthread_mutexattr_getpshared)
 247
 248 int __pthread_mutexattr_setpshared (pthread_mutexattr_t *attr attribute_unused, int pshared) attribute_hidden;
 249 int __pthread_mutexattr_setpshared (pthread_mutexattr_t *attr attribute_unused, int pshared)
 250 {
 251   if (pshared != PTHREAD_PROCESS_PRIVATE && pshared != PTHREAD_PROCESS_SHARED)
 252     return EINVAL;
 253
 254   /* For now it is not possible to shared a conditional variable.  */
 255   if (pshared != PTHREAD_PROCESS_PRIVATE)
 256     return ENOSYS;
 257
 258   return 0;
 259 }
 260 weak_alias (__pthread_mutexattr_setpshared, pthread_mutexattr_setpshared)
 261
 262 /* Once-only execution */
 263
 264 static pthread_mutex_t once_masterlock = PTHREAD_MUTEX_INITIALIZER;
 265 static pthread_cond_t once_finished = PTHREAD_COND_INITIALIZER;
 266 static int fork_generation = 0; /* Child process increments this after fork. */
 267
 268 enum { NEVER = 0, IN_PROGRESS = 1, DONE = 2 };
 269
 270 /* If a thread is canceled while calling the init_routine out of
 271    pthread once, this handler will reset the once_control variable
 272    to the NEVER state. */
 273
 274 static void pthread_once_cancelhandler(void *arg)
 275 {
 276     pthread_once_t *once_control = arg;
 277
 278     __pthread_mutex_lock(&once_masterlock);
 279     *once_control = NEVER;
 280     __pthread_mutex_unlock(&once_masterlock);
 281     pthread_cond_broadcast(&once_finished);
 282 }
 283
 284 int __pthread_once(pthread_once_t * once_control, void (*init_routine)(void))
 285 {
 286   /* flag for doing the condition broadcast outside of mutex */
 287   int state_changed;
 288
 289   /* Test without locking first for speed */
 290   if (*once_control == DONE) {
 291     READ_MEMORY_BARRIER();
 292     return 0;
 293   }
 294   /* Lock and test again */
 295
 296   state_changed = 0;
 297
 298   __pthread_mutex_lock(&once_masterlock);
 299
 300   /* If this object was left in an IN_PROGRESS state in a parent
 301      process (indicated by stale generation field), reset it to NEVER. */
 302   if ((*once_control & 3) == IN_PROGRESS && (*once_control & ~3) != fork_generation)
 303     *once_control = NEVER;
 304
 305   /* If init_routine is being called from another routine, wait until
 306      it completes. */
 307   while ((*once_control & 3) == IN_PROGRESS) {
 308     pthread_cond_wait(&once_finished, &once_masterlock);
 309   }
 310   /* Here *once_control is stable and either NEVER or DONE. */
 311   if (*once_control == NEVER) {
 312     *once_control = IN_PROGRESS | fork_generation;
 313     __pthread_mutex_unlock(&once_masterlock);
 314     pthread_cleanup_push(pthread_once_cancelhandler, once_control);
 315     init_routine();
 316     pthread_cleanup_pop(0);
 317     __pthread_mutex_lock(&once_masterlock);
 318     WRITE_MEMORY_BARRIER();
 319     *once_control = DONE;
 320     state_changed = 1;
 321   }
 322   __pthread_mutex_unlock(&once_masterlock);
 323
 324   if (state_changed)
 325     pthread_cond_broadcast(&once_finished);
 326
 327   return 0;
 328 }
 329 strong_alias (__pthread_once, pthread_once)
 330
 331 /*
 332  * Handle the state of the pthread_once mechanism across forks.  The
 333  * once_masterlock is acquired in the parent process prior to a fork to ensure
 334  * that no thread is in the critical region protected by the lock.  After the
 335  * fork, the lock is released. In the child, the lock and the condition
 336  * variable are simply reset.  The child also increments its generation
 337  * counter which lets pthread_once calls detect stale IN_PROGRESS states
 338  * and reset them back to NEVER.
 339  */
 340
 341 void __pthread_once_fork_prepare(void);
 342 void __pthread_once_fork_prepare(void)
 343 {
 344   __pthread_mutex_lock(&once_masterlock);
 345 }
 346
 347 void __pthread_once_fork_parent(void);
 348 void __pthread_once_fork_parent(void)
 349 {
 350   __pthread_mutex_unlock(&once_masterlock);
 351 }
 352
 353 void __pthread_once_fork_child(void);
 354 void __pthread_once_fork_child(void)
 355 {
 356   __pthread_mutex_init(&once_masterlock, NULL);
 357   pthread_cond_init(&once_finished, NULL);
 358   if (fork_generation <= INT_MAX - 4)
 359     fork_generation += 4;       /* leave least significant two bits zero */
 360   else
 361     fork_generation = 0;
 362 }