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