nptl/pthread_cond_wait.c

   1 /* Copyright (C) 2003, 2004, 2006 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <endian.h>
  21 #include <errno.h>
  22 #include <sysdep.h>
  23 #include <lowlevellock.h>
  24 #include <pthread.h>
  25 #include <pthreadP.h>
  26
  27 #include <shlib-compat.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
  47   /* We are going to modify shared data.  */
  48   lll_mutex_lock (cbuffer->cond->__data.__lock);
  49
  50   if (cbuffer->bc_seq == cbuffer->cond->__data.__broadcast_seq)
  51     {
  52       /* This thread is not waiting anymore.  Adjust the sequence counters
  53          appropriately.  We do not increment WAKEUP_SEQ if this would
  54          bump it over the value of TOTAL_SEQ.  This can happen if a thread
  55          was woken and then canceled.  */
  56       if (cbuffer->cond->__data.__wakeup_seq
  57           < cbuffer->cond->__data.__total_seq)
  58         {
  59           ++cbuffer->cond->__data.__wakeup_seq;
  60           ++cbuffer->cond->__data.__futex;
  61         }
  62       ++cbuffer->cond->__data.__woken_seq;
  63     }
  64
  65   cbuffer->cond->__data.__nwaiters -= 1 << COND_CLOCK_BITS;
  66
  67   /* If pthread_cond_destroy was called on this variable already,
  68      notify the pthread_cond_destroy caller all waiters have left
  69      and it can be successfully destroyed.  */
  70   destroying = 0;
  71   if (cbuffer->cond->__data.__total_seq == -1ULL
  72       && cbuffer->cond->__data.__nwaiters < (1 << COND_CLOCK_BITS))
  73     {
  74       lll_futex_wake (&cbuffer->cond->__data.__nwaiters, 1);
  75       destroying = 1;
  76     }
  77
  78   /* We are done.  */
  79   lll_mutex_unlock (cbuffer->cond->__data.__lock);
  80
  81   /* Wake everybody to make sure no condvar signal gets lost.  */
  82   if (! destroying)
  83     lll_futex_wake (&cbuffer->cond->__data.__futex, INT_MAX);
  84
  85   /* Get the mutex before returning unless asynchronous cancellation
  86      is in effect.  */
  87   __pthread_mutex_cond_lock (cbuffer->mutex);
  88 }
  89
  90
  91 int
  92 __pthread_cond_wait (cond, mutex)
  93      pthread_cond_t *cond;
  94      pthread_mutex_t *mutex;
  95 {
  96   struct _pthread_cleanup_buffer buffer;
  97   struct _condvar_cleanup_buffer cbuffer;
  98   int err;
  99
 100   /* Make sure we are along.  */
 101   lll_mutex_lock (cond->__data.__lock);
 102
 103   /* Now we can release the mutex.  */
 104   err = __pthread_mutex_unlock_usercnt (mutex, 0);
 105   if (__builtin_expect (err, 0))
 106     {
 107       lll_mutex_unlock (cond->__data.__lock);
 108       return err;
 109     }
 110
 111   /* We have one new user of the condvar.  */
 112   ++cond->__data.__total_seq;
 113   ++cond->__data.__futex;
 114   cond->__data.__nwaiters += 1 << COND_CLOCK_BITS;
 115
 116   /* Remember the mutex we are using here.  If there is already a
 117      different address store this is a bad user bug.  Do not store
 118      anything for pshared condvars.  */
 119   if (cond->__data.__mutex != (void *) ~0l)
 120     cond->__data.__mutex = mutex;
 121
 122   /* Prepare structure passed to cancellation handler.  */
 123   cbuffer.cond = cond;
 124   cbuffer.mutex = mutex;
 125
 126   /* Before we block we enable cancellation.  Therefore we have to
 127      install a cancellation handler.  */
 128   __pthread_cleanup_push (&buffer, __condvar_cleanup, &cbuffer);
 129
 130   /* The current values of the wakeup counter.  The "woken" counter
 131      must exceed this value.  */
 132   unsigned long long int val;
 133   unsigned long long int seq;
 134   val = seq = cond->__data.__wakeup_seq;
 135   /* Remember the broadcast counter.  */
 136   cbuffer.bc_seq = cond->__data.__broadcast_seq;
 137
 138   do
 139     {
 140       unsigned int futex_val = cond->__data.__futex;
 141
 142       /* Prepare to wait.  Release the condvar futex.  */
 143       lll_mutex_unlock (cond->__data.__lock);
 144
 145       /* Enable asynchronous cancellation.  Required by the standard.  */
 146       cbuffer.oldtype = __pthread_enable_asynccancel ();
 147
 148       /* Wait until woken by signal or broadcast.  */
 149       lll_futex_wait (&cond->__data.__futex, futex_val);
 150
 151       /* Disable asynchronous cancellation.  */
 152       __pthread_disable_asynccancel (cbuffer.oldtype);
 153
 154       /* We are going to look at shared data again, so get the lock.  */
 155       lll_mutex_lock (cond->__data.__lock);
 156
 157       /* If a broadcast happened, we are done.  */
 158       if (cbuffer.bc_seq != cond->__data.__broadcast_seq)
 159         goto bc_out;
 160
 161       /* Check whether we are eligible for wakeup.  */
 162       val = cond->__data.__wakeup_seq;
 163     }
 164   while (val == seq || cond->__data.__woken_seq == val);
 165
 166   /* Another thread woken up.  */
 167   ++cond->__data.__woken_seq;
 168
 169  bc_out:
 170
 171   cond->__data.__nwaiters -= 1 << COND_CLOCK_BITS;
 172
 173   /* If pthread_cond_destroy was called on this varaible already,
 174      notify the pthread_cond_destroy caller all waiters have left
 175      and it can be successfully destroyed.  */
 176   if (cond->__data.__total_seq == -1ULL
 177       && cond->__data.__nwaiters < (1 << COND_CLOCK_BITS))
 178     lll_futex_wake (&cond->__data.__nwaiters, 1);
 179
 180   /* We are done with the condvar.  */
 181   lll_mutex_unlock (cond->__data.__lock);
 182
 183   /* The cancellation handling is back to normal, remove the handler.  */
 184   __pthread_cleanup_pop (&buffer, 0);
 185
 186   /* Get the mutex before returning.  */
 187   return __pthread_mutex_cond_lock (mutex);
 188 }
 189
 190 versioned_symbol (libpthread, __pthread_cond_wait, pthread_cond_wait,
 191                   GLIBC_2_3_2);