nptl/pthread_mutex_trylock.c

   1 /* Copyright (C) 2002, 2003, 2005, 2006 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library 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 GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <stdlib.h>
  23 #include "pthreadP.h"
  24 #include <lowlevellock.h>
  25
  26
  27 int
  28 __pthread_mutex_trylock (mutex)
  29      pthread_mutex_t *mutex;
  30 {
  31   int oldval;
  32   pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
  33
  34   switch (__builtin_expect (mutex->__data.__kind, PTHREAD_MUTEX_TIMED_NP))
  35     {
  36       /* Recursive mutex.  */
  37     case PTHREAD_MUTEX_RECURSIVE_NP:
  38       /* Check whether we already hold the mutex.  */
  39       if (mutex->__data.__owner == id)
  40         {
  41           /* Just bump the counter.  */
  42           if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
  43             /* Overflow of the counter.  */
  44             return EAGAIN;
  45
  46           ++mutex->__data.__count;
  47           return 0;
  48         }
  49
  50       if (lll_mutex_trylock (mutex->__data.__lock) == 0)
  51         {
  52           /* Record the ownership.  */
  53           mutex->__data.__owner = id;
  54           mutex->__data.__count = 1;
  55           ++mutex->__data.__nusers;
  56           return 0;
  57         }
  58       break;
  59
  60     case PTHREAD_MUTEX_ERRORCHECK_NP:
  61       /* Check whether we already hold the mutex.  */
  62       if (__builtin_expect (mutex->__data.__owner == id, 0))
  63         return EDEADLK;
  64
  65       /* FALLTHROUGH */
  66
  67     case PTHREAD_MUTEX_TIMED_NP:
  68     case PTHREAD_MUTEX_ADAPTIVE_NP:
  69       /* Normal mutex.  */
  70       if (lll_mutex_trylock (mutex->__data.__lock) != 0)
  71         break;
  72
  73       /* Record the ownership.  */
  74       mutex->__data.__owner = id;
  75       ++mutex->__data.__nusers;
  76
  77       return 0;
  78
  79
  80     case PTHREAD_MUTEX_ROBUST_PRIVATE_RECURSIVE_NP:
  81     case PTHREAD_MUTEX_ROBUST_PRIVATE_ERRORCHECK_NP:
  82     case PTHREAD_MUTEX_ROBUST_PRIVATE_NP:
  83     case PTHREAD_MUTEX_ROBUST_PRIVATE_ADAPTIVE_NP:
  84       oldval = mutex->__data.__lock;
  85       do
  86         {
  87           if ((oldval & FUTEX_OWNER_DIED) != 0)
  88             {
  89               /* The previous owner died.  Try locking the mutex.  */
  90               int newval;
  91               while ((newval
  92                       = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  93                                                              id, oldval))
  94                      != oldval)
  95                 {
  96                   if ((newval & FUTEX_OWNER_DIED) == 0)
  97                     goto normal;
  98                   oldval = newval;
  99                 }
 100
 101               /* We got the mutex.  */
 102               mutex->__data.__count = 1;
 103               /* But it is inconsistent unless marked otherwise.  */
 104               mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 105
 106               ENQUEUE_MUTEX (mutex);
 107
 108               /* Note that we deliberately exist here.  If we fall
 109                  through to the end of the function __nusers would be
 110                  incremented which is not correct because the old
 111                  owner has to be discounted.  */
 112               return EOWNERDEAD;
 113             }
 114
 115         normal:
 116           /* Check whether we already hold the mutex.  */
 117           if (__builtin_expect ((mutex->__data.__lock & FUTEX_TID_MASK)
 118                                 == id, 0))
 119             {
 120               if (mutex->__data.__kind
 121                   == PTHREAD_MUTEX_ROBUST_PRIVATE_ERRORCHECK_NP)
 122                 return EDEADLK;
 123
 124               if (mutex->__data.__kind
 125                   == PTHREAD_MUTEX_ROBUST_PRIVATE_RECURSIVE_NP)
 126                 {
 127                   /* Just bump the counter.  */
 128                   if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
 129                     /* Overflow of the counter.  */
 130                     return EAGAIN;
 131
 132                   ++mutex->__data.__count;
 133
 134                   return 0;
 135                 }
 136             }
 137
 138           oldval = lll_robust_mutex_trylock (mutex->__data.__lock, id);
 139           if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
 140             return EBUSY;
 141
 142         robust:
 143           if (__builtin_expect (mutex->__data.__owner
 144                                 == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 145             {
 146               /* This mutex is now not recoverable.  */
 147               mutex->__data.__count = 0;
 148               if (oldval == id)
 149                 lll_mutex_unlock (mutex->__data.__lock);
 150               return ENOTRECOVERABLE;
 151             }
 152         }
 153       while ((oldval & FUTEX_OWNER_DIED) != 0);
 154
 155       ENQUEUE_MUTEX (mutex);
 156
 157       mutex->__data.__owner = id;
 158       ++mutex->__data.__nusers;
 159       mutex->__data.__count = 1;
 160
 161       return 0;
 162
 163     default:
 164       /* Correct code cannot set any other type.  */
 165       return EINVAL;
 166     }
 167
 168   return EBUSY;
 169 }
 170 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)