nptl/pthread_cond_wait.c

   1 /* Copyright (C) 2003-2014 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 struct _condvar_cleanup_buffer
  30 {
  31   int oldtype;
  32   pthread_cond_t *cond;
  33   pthread_mutex_t *mutex;
  34   unsigned int bc_seq;
  35 };
  36
  37
  38 void
  39 __attribute__ ((visibility ("hidden")))
  40 __condvar_cleanup (void *arg)
  41 {
  42   struct _condvar_cleanup_buffer *cbuffer =
  43     (struct _condvar_cleanup_buffer *) arg;
  44   unsigned int destroying;
  45   int pshared = (cbuffer->cond->__data.__mutex == (void *) ~0l)
  46                 ? LLL_SHARED : LLL_PRIVATE;
  47
  48   /* We are going to modify shared data.  */
  49   lll_lock (cbuffer->cond->__data.__lock, pshared);
  50
  51   if (cbuffer->bc_seq == cbuffer->cond->__data.__broadcast_seq)
  52     {
  53       /* This thread is not waiting anymore.  Adjust the sequence counters
  54          appropriately.  We do not increment WAKEUP_SEQ if this would
  55          bump it over the value of TOTAL_SEQ.  This can happen if a thread
  56          was woken and then canceled.  */
  57       if (cbuffer->cond->__data.__wakeup_seq
  58           < cbuffer->cond->__data.__total_seq)
  59         {
  60           ++cbuffer->cond->__data.__wakeup_seq;
  61           ++cbuffer->cond->__data.__futex;
  62         }
  63       ++cbuffer->cond->__data.__woken_seq;
  64     }
  65
  66   cbuffer->cond->__data.__nwaiters -= 1 << COND_NWAITERS_SHIFT;
  67
  68   /* If pthread_cond_destroy was called on this variable already,
  69      notify the pthread_cond_destroy caller all waiters have left
  70      and it can be successfully destroyed.  */
  71   destroying = 0;
  72   if (cbuffer->cond->__data.__total_seq == -1ULL
  73       && cbuffer->cond->__data.__nwaiters < (1 << COND_NWAITERS_SHIFT))
  74     {
  75       lll_futex_wake (&cbuffer->cond->__data.__nwaiters, 1, pshared);
  76       destroying = 1;
  77     }
  78
  79   /* We are done.  */
  80   lll_unlock (cbuffer->cond->__data.__lock, pshared);
  81
  82   /* Wake everybody to make sure no condvar signal gets lost.  */
  83   if (! destroying)
  84     lll_futex_wake (&cbuffer->cond->__data.__futex, INT_MAX, pshared);
  85
  86   /* Get the mutex before returning unless asynchronous cancellation
  87      is in effect.  We don't try to get the mutex if we already own it.  */
  88   if (!(USE_REQUEUE_PI (cbuffer->mutex))
  89       || ((cbuffer->mutex->__data.__lock & FUTEX_TID_MASK)
  90           != THREAD_GETMEM (THREAD_SELF, tid)))
  91   {
  92     __pthread_mutex_cond_lock (cbuffer->mutex);
  93   }
  94   else
  95     __pthread_mutex_cond_lock_adjust (cbuffer->mutex);
  96 }
  97
  98
  99 int
 100 __pthread_cond_wait (cond, mutex)
 101      pthread_cond_t *cond;
 102      pthread_mutex_t *mutex;
 103 {
 104   struct _pthread_cleanup_buffer buffer;
 105   struct _condvar_cleanup_buffer cbuffer;
 106   int err;
 107   int pshared = (cond->__data.__mutex == (void *) ~0l)
 108                 ? LLL_SHARED : LLL_PRIVATE;
 109
 110 #if (defined lll_futex_wait_requeue_pi \
 111      && defined __ASSUME_REQUEUE_PI)
 112   int pi_flag = 0;
 113 #endif
 114
 115   LIBC_PROBE (cond_wait, 2, cond, mutex);
 116
 117   /* Make sure we are alone.  */
 118   lll_lock (cond->__data.__lock, pshared);
 119
 120   /* Now we can release the mutex.  */
 121   err = __pthread_mutex_unlock_usercnt (mutex, 0);
 122   if (__builtin_expect (err, 0))
 123     {
 124       lll_unlock (cond->__data.__lock, pshared);
 125       return err;
 126     }
 127
 128   /* We have one new user of the condvar.  */
 129   ++cond->__data.__total_seq;
 130   ++cond->__data.__futex;
 131   cond->__data.__nwaiters += 1 << COND_NWAITERS_SHIFT;
 132
 133   /* Remember the mutex we are using here.  If there is already a
 134      different address store this is a bad user bug.  Do not store
 135      anything for pshared condvars.  */
 136   if (cond->__data.__mutex != (void *) ~0l)
 137     cond->__data.__mutex = mutex;
 138
 139   /* Prepare structure passed to cancellation handler.  */
 140   cbuffer.cond = cond;
 141   cbuffer.mutex = mutex;
 142
 143   /* Before we block we enable cancellation.  Therefore we have to
 144      install a cancellation handler.  */
 145   __pthread_cleanup_push (&buffer, __condvar_cleanup, &cbuffer);
 146
 147   /* The current values of the wakeup counter.  The "woken" counter
 148      must exceed this value.  */
 149   unsigned long long int val;
 150   unsigned long long int seq;
 151   val = seq = cond->__data.__wakeup_seq;
 152   /* Remember the broadcast counter.  */
 153   cbuffer.bc_seq = cond->__data.__broadcast_seq;
 154
 155   do
 156     {
 157       unsigned int futex_val = cond->__data.__futex;
 158       /* Prepare to wait.  Release the condvar futex.  */
 159       lll_unlock (cond->__data.__lock, pshared);
 160
 161       /* Enable asynchronous cancellation.  Required by the standard.  */
 162       cbuffer.oldtype = __pthread_enable_asynccancel ();
 163
 164 #if (defined lll_futex_wait_requeue_pi \
 165      && defined __ASSUME_REQUEUE_PI)
 166       /* If pi_flag remained 1 then it means that we had the lock and the mutex
 167          but a spurious waker raced ahead of us.  Give back the mutex before
 168          going into wait again.  */
 169       if (pi_flag)
 170         {
 171           __pthread_mutex_cond_lock_adjust (mutex);
 172           __pthread_mutex_unlock_usercnt (mutex, 0);
 173         }
 174       pi_flag = USE_REQUEUE_PI (mutex);
 175
 176       if (pi_flag)
 177         {
 178           err = lll_futex_wait_requeue_pi (&cond->__data.__futex,
 179                                            futex_val, &mutex->__data.__lock,
 180                                            pshared);
 181
 182           pi_flag = (err == 0);
 183         }
 184       else
 185 #endif
 186           /* Wait until woken by signal or broadcast.  */
 187         lll_futex_wait (&cond->__data.__futex, futex_val, pshared);
 188
 189       /* Disable asynchronous cancellation.  */
 190       __pthread_disable_asynccancel (cbuffer.oldtype);
 191
 192       /* We are going to look at shared data again, so get the lock.  */
 193       lll_lock (cond->__data.__lock, pshared);
 194
 195       /* If a broadcast happened, we are done.  */
 196       if (cbuffer.bc_seq != cond->__data.__broadcast_seq)
 197         goto bc_out;
 198
 199       /* Check whether we are eligible for wakeup.  */
 200       val = cond->__data.__wakeup_seq;
 201     }
 202   while (val == seq || cond->__data.__woken_seq == val);
 203
 204   /* Another thread woken up.  */
 205   ++cond->__data.__woken_seq;
 206
 207  bc_out:
 208
 209   cond->__data.__nwaiters -= 1 << COND_NWAITERS_SHIFT;
 210
 211   /* If pthread_cond_destroy was called on this varaible already,
 212      notify the pthread_cond_destroy caller all waiters have left
 213      and it can be successfully destroyed.  */
 214   if (cond->__data.__total_seq == -1ULL
 215       && cond->__data.__nwaiters < (1 << COND_NWAITERS_SHIFT))
 216     lll_futex_wake (&cond->__data.__nwaiters, 1, pshared);
 217
 218   /* We are done with the condvar.  */
 219   lll_unlock (cond->__data.__lock, pshared);
 220
 221   /* The cancellation handling is back to normal, remove the handler.  */
 222   __pthread_cleanup_pop (&buffer, 0);
 223
 224   /* Get the mutex before returning.  Not needed for PI.  */
 225 #if (defined lll_futex_wait_requeue_pi \
 226      && defined __ASSUME_REQUEUE_PI)
 227   if (pi_flag)
 228     {
 229       __pthread_mutex_cond_lock_adjust (mutex);
 230       return 0;
 231     }
 232   else
 233 #endif
 234     return __pthread_mutex_cond_lock (mutex);
 235 }
 236
 237 versioned_symbol (libpthread, __pthread_cond_wait, pthread_cond_wait,
 238                   GLIBC_2_3_2);