nptl/pthread_cond_wait.c

   1 /* Copyright (C) 2003-2012 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
   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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <endian.h>
  20 #include <errno.h>
  21 #include <sysdep.h>
  22 #include <lowlevellock.h>
  23 #include <pthread.h>
  24 #include <pthreadP.h>
  25
  26 #include <shlib-compat.h>
  27 #include <stap-probe.h>
  28
  29
  30 struct _condvar_cleanup_buffer
  31 {
  32   int oldtype;
  33   pthread_cond_t *cond;
  34   pthread_mutex_t *mutex;
  35   unsigned int bc_seq;
  36 };
  37
  38
  39 void
  40 __attribute__ ((visibility ("hidden")))
  41 __condvar_cleanup (void *arg)
  42 {
  43   struct _condvar_cleanup_buffer *cbuffer =
  44     (struct _condvar_cleanup_buffer *) arg;
  45   unsigned int destroying;
  46   int pshared = (cbuffer->cond->__data.__mutex == (void *) ~0l)
  47                 ? LLL_SHARED : LLL_PRIVATE;
  48
  49   /* We are going to modify shared data.  */
  50   lll_lock (cbuffer->cond->__data.__lock, pshared);
  51
  52   if (cbuffer->bc_seq == cbuffer->cond->__data.__broadcast_seq)
  53     {
  54       /* This thread is not waiting anymore.  Adjust the sequence counters
  55          appropriately.  We do not increment WAKEUP_SEQ if this would
  56          bump it over the value of TOTAL_SEQ.  This can happen if a thread
  57          was woken and then canceled.  */
  58       if (cbuffer->cond->__data.__wakeup_seq
  59           < cbuffer->cond->__data.__total_seq)
  60         {
  61           ++cbuffer->cond->__data.__wakeup_seq;
  62           ++cbuffer->cond->__data.__futex;
  63         }
  64       ++cbuffer->cond->__data.__woken_seq;
  65     }
  66
  67   cbuffer->cond->__data.__nwaiters -= 1 << COND_NWAITERS_SHIFT;
  68
  69   /* If pthread_cond_destroy was called on this variable already,
  70      notify the pthread_cond_destroy caller all waiters have left
  71      and it can be successfully destroyed.  */
  72   destroying = 0;
  73   if (cbuffer->cond->__data.__total_seq == -1ULL
  74       && cbuffer->cond->__data.__nwaiters < (1 << COND_NWAITERS_SHIFT))
  75     {
  76       lll_futex_wake (&cbuffer->cond->__data.__nwaiters, 1, pshared);
  77       destroying = 1;
  78     }
  79
  80   /* We are done.  */
  81   lll_unlock (cbuffer->cond->__data.__lock, pshared);
  82
  83   /* Wake everybody to make sure no condvar signal gets lost.  */
  84   if (! destroying)
  85     lll_futex_wake (&cbuffer->cond->__data.__futex, INT_MAX, pshared);
  86
  87   /* Get the mutex before returning unless asynchronous cancellation
  88      is in effect.  */
  89   __pthread_mutex_cond_lock (cbuffer->mutex);
  90 }
  91
  92
  93 int
  94 __pthread_cond_wait (cond, mutex)
  95      pthread_cond_t *cond;
  96      pthread_mutex_t *mutex;
  97 {
  98   struct _pthread_cleanup_buffer buffer;
  99   struct _condvar_cleanup_buffer cbuffer;
 100   int err;
 101   int pshared = (cond->__data.__mutex == (void *) ~0l)
 102                 ? LLL_SHARED : LLL_PRIVATE;
 103
 104   LIBC_PROBE (cond_wait, 2, cond, mutex);
 105
 106   /* Make sure we are alone.  */
 107   lll_lock (cond->__data.__lock, pshared);
 108
 109   /* Now we can release the mutex.  */
 110   err = __pthread_mutex_unlock_usercnt (mutex, 0);
 111   if (__builtin_expect (err, 0))
 112     {
 113       lll_unlock (cond->__data.__lock, pshared);
 114       return err;
 115     }
 116
 117   /* We have one new user of the condvar.  */
 118   ++cond->__data.__total_seq;
 119   ++cond->__data.__futex;
 120   cond->__data.__nwaiters += 1 << COND_NWAITERS_SHIFT;
 121
 122   /* Remember the mutex we are using here.  If there is already a
 123      different address store this is a bad user bug.  Do not store
 124      anything for pshared condvars.  */
 125   if (cond->__data.__mutex != (void *) ~0l)
 126     cond->__data.__mutex = mutex;
 127
 128   /* Prepare structure passed to cancellation handler.  */
 129   cbuffer.cond = cond;
 130   cbuffer.mutex = mutex;
 131
 132   /* Before we block we enable cancellation.  Therefore we have to
 133      install a cancellation handler.  */
 134   __pthread_cleanup_push (&buffer, __condvar_cleanup, &cbuffer);
 135
 136   /* The current values of the wakeup counter.  The "woken" counter
 137      must exceed this value.  */
 138   unsigned long long int val;
 139   unsigned long long int seq;
 140   val = seq = cond->__data.__wakeup_seq;
 141   /* Remember the broadcast counter.  */
 142   cbuffer.bc_seq = cond->__data.__broadcast_seq;
 143
 144   do
 145     {
 146       unsigned int futex_val = cond->__data.__futex;
 147
 148       /* Prepare to wait.  Release the condvar futex.  */
 149       lll_unlock (cond->__data.__lock, pshared);
 150
 151       /* Enable asynchronous cancellation.  Required by the standard.  */
 152       cbuffer.oldtype = __pthread_enable_asynccancel ();
 153
 154       /* Wait until woken by signal or broadcast.  */
 155       lll_futex_wait (&cond->__data.__futex, futex_val, pshared);
 156
 157       /* Disable asynchronous cancellation.  */
 158       __pthread_disable_asynccancel (cbuffer.oldtype);
 159
 160       /* We are going to look at shared data again, so get the lock.  */
 161       lll_lock (cond->__data.__lock, pshared);
 162
 163       /* If a broadcast happened, we are done.  */
 164       if (cbuffer.bc_seq != cond->__data.__broadcast_seq)
 165         goto bc_out;
 166
 167       /* Check whether we are eligible for wakeup.  */
 168       val = cond->__data.__wakeup_seq;
 169     }
 170   while (val == seq || cond->__data.__woken_seq == val);
 171
 172   /* Another thread woken up.  */
 173   ++cond->__data.__woken_seq;
 174
 175  bc_out:
 176
 177   cond->__data.__nwaiters -= 1 << COND_NWAITERS_SHIFT;
 178
 179   /* If pthread_cond_destroy was called on this varaible already,
 180      notify the pthread_cond_destroy caller all waiters have left
 181      and it can be successfully destroyed.  */
 182   if (cond->__data.__total_seq == -1ULL
 183       && cond->__data.__nwaiters < (1 << COND_NWAITERS_SHIFT))
 184     lll_futex_wake (&cond->__data.__nwaiters, 1, pshared);
 185
 186   /* We are done with the condvar.  */
 187   lll_unlock (cond->__data.__lock, pshared);
 188
 189   /* The cancellation handling is back to normal, remove the handler.  */
 190   __pthread_cleanup_pop (&buffer, 0);
 191
 192   /* Get the mutex before returning.  */
 193   return __pthread_mutex_cond_lock (mutex);
 194 }
 195
 196 versioned_symbol (libpthread, __pthread_cond_wait, pthread_cond_wait,
 197                   GLIBC_2_3_2);