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_RECURSIVE_NP:
  81     case PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP:
  82     case PTHREAD_MUTEX_ROBUST_NORMAL_NP:
  83     case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
  84       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
  85                      &mutex->__data.__list.__next);
  86
  87       oldval = mutex->__data.__lock;
  88       do
  89         {
  90         again:
  91           if ((oldval & FUTEX_OWNER_DIED) != 0)
  92             {
  93               /* The previous owner died.  Try locking the mutex.  */
  94               int newval
  95                 = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
  96                                                        id, oldval);
  97
  98               if (newval != oldval)
  99                 {
 100                   oldval = newval;
 101                   goto again;
 102                 }
 103
 104               /* We got the mutex.  */
 105               mutex->__data.__count = 1;
 106               /* But it is inconsistent unless marked otherwise.  */
 107               mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
 108
 109               ENQUEUE_MUTEX (mutex);
 110               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 111
 112               /* Note that we deliberately exist here.  If we fall
 113                  through to the end of the function __nusers would be
 114                  incremented which is not correct because the old
 115                  owner has to be discounted.  */
 116               return EOWNERDEAD;
 117             }
 118
 119           /* Check whether we already hold the mutex.  */
 120           if (__builtin_expect ((oldval & FUTEX_TID_MASK) == id, 0))
 121             {
 122               if (mutex->__data.__kind
 123                   == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
 124                 {
 125                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 126                                  NULL);
 127                   return EDEADLK;
 128                 }
 129
 130               if (mutex->__data.__kind
 131                   == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
 132                 {
 133                   THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
 134                                  NULL);
 135
 136                   /* Just bump the counter.  */
 137                   if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
 138                     /* Overflow of the counter.  */
 139                     return EAGAIN;
 140
 141                   ++mutex->__data.__count;
 142
 143                   return 0;
 144                 }
 145             }
 146
 147           oldval = lll_robust_mutex_trylock (mutex->__data.__lock, id);
 148           if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
 149             {
 150               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 151
 152               return EBUSY;
 153             }
 154
 155         robust:
 156           if (__builtin_expect (mutex->__data.__owner
 157                                 == PTHREAD_MUTEX_NOTRECOVERABLE, 0))
 158             {
 159               /* This mutex is now not recoverable.  */
 160               mutex->__data.__count = 0;
 161               if (oldval == id)
 162                 lll_mutex_unlock (mutex->__data.__lock);
 163               THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 164               return ENOTRECOVERABLE;
 165             }
 166         }
 167       while ((oldval & FUTEX_OWNER_DIED) != 0);
 168
 169       ENQUEUE_MUTEX (mutex);
 170       THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
 171
 172       mutex->__data.__owner = id;
 173       ++mutex->__data.__nusers;
 174       mutex->__data.__count = 1;
 175
 176       return 0;
 177
 178     default:
 179       /* Correct code cannot set any other type.  */
 180       return EINVAL;
 181     }
 182
 183   return EBUSY;
 184 }
 185 strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)