nptl/pthread_cond_wait.c

   1 /* Copyright (C) 2003-2016 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 #include <kernel-features.h>
  26
  27 #include <shlib-compat.h>
  28 #include <stap-probe.h>
  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.  We don't try to get the mutex if we already own it.  */
  89   if (!(USE_REQUEUE_PI (cbuffer->mutex))
  90       || ((cbuffer->mutex->__data.__lock & FUTEX_TID_MASK)
  91           != THREAD_GETMEM (THREAD_SELF, tid)))
  92   {
  93     __pthread_mutex_cond_lock (cbuffer->mutex);
  94   }
  95   else
  96     __pthread_mutex_cond_lock_adjust (cbuffer->mutex);
  97 }
  98
  99
 100 int
 101 __pthread_cond_wait (pthread_cond_t *cond, pthread_mutex_t *mutex)
 102 {
 103   struct _pthread_cleanup_buffer buffer;
 104   struct _condvar_cleanup_buffer cbuffer;
 105   int err;
 106   int pshared = (cond->__data.__mutex == (void *) ~0l)
 107                 ? LLL_SHARED : LLL_PRIVATE;
 108
 109 #if (defined lll_futex_wait_requeue_pi \
 110      && defined __ASSUME_REQUEUE_PI)
 111   int pi_flag = 0;
 112 #endif
 113
 114   LIBC_PROBE (cond_wait, 2, cond, mutex);
 115
 116   /* Make sure we are alone.  */
 117   lll_lock (cond->__data.__lock, pshared);
 118
 119   /* Now we can release the mutex.  */
 120   err = __pthread_mutex_unlock_usercnt (mutex, 0);
 121   if (__glibc_unlikely (err))
 122     {
 123       lll_unlock (cond->__data.__lock, pshared);
 124       return err;
 125     }
 126
 127   /* We have one new user of the condvar.  */
 128   ++cond->__data.__total_seq;
 129   ++cond->__data.__futex;
 130   cond->__data.__nwaiters += 1 << COND_NWAITERS_SHIFT;
 131
 132   /* Remember the mutex we are using here.  If there is already a
 133      different address store this is a bad user bug.  Do not store
 134      anything for pshared condvars.  */
 135   if (cond->__data.__mutex != (void *) ~0l)
 136     cond->__data.__mutex = mutex;
 137
 138   /* Prepare structure passed to cancellation handler.  */
 139   cbuffer.cond = cond;
 140   cbuffer.mutex = mutex;
 141
 142   /* Before we block we enable cancellation.  Therefore we have to
 143      install a cancellation handler.  */
 144   __pthread_cleanup_push (&buffer, __condvar_cleanup, &cbuffer);
 145
 146   /* The current values of the wakeup counter.  The "woken" counter
 147      must exceed this value.  */
 148   unsigned long long int val;
 149   unsigned long long int seq;
 150   val = seq = cond->__data.__wakeup_seq;
 151   /* Remember the broadcast counter.  */
 152   cbuffer.bc_seq = cond->__data.__broadcast_seq;
 153
 154   do
 155     {
 156       unsigned int futex_val = cond->__data.__futex;
 157       /* Prepare to wait.  Release the condvar futex.  */
 158       lll_unlock (cond->__data.__lock, pshared);
 159
 160       /* Enable asynchronous cancellation.  Required by the standard.  */
 161       cbuffer.oldtype = __pthread_enable_asynccancel ();
 162
 163 #if (defined lll_futex_wait_requeue_pi \
 164      && defined __ASSUME_REQUEUE_PI)
 165       /* If pi_flag remained 1 then it means that we had the lock and the mutex
 166          but a spurious waker raced ahead of us.  Give back the mutex before
 167          going into wait again.  */
 168       if (pi_flag)
 169         {
 170           __pthread_mutex_cond_lock_adjust (mutex);
 171           __pthread_mutex_unlock_usercnt (mutex, 0);
 172         }
 173       pi_flag = USE_REQUEUE_PI (mutex);
 174
 175       if (pi_flag)
 176         {
 177           err = lll_futex_wait_requeue_pi (&cond->__data.__futex,
 178                                            futex_val, &mutex->__data.__lock,
 179                                            pshared);
 180
 181           pi_flag = (err == 0);
 182         }
 183       else
 184 #endif
 185           /* Wait until woken by signal or broadcast.  */
 186         lll_futex_wait (&cond->__data.__futex, futex_val, pshared);
 187
 188       /* Disable asynchronous cancellation.  */
 189       __pthread_disable_asynccancel (cbuffer.oldtype);
 190
 191       /* We are going to look at shared data again, so get the lock.  */
 192       lll_lock (cond->__data.__lock, pshared);
 193
 194       /* If a broadcast happened, we are done.  */
 195       if (cbuffer.bc_seq != cond->__data.__broadcast_seq)
 196         goto bc_out;
 197
 198       /* Check whether we are eligible for wakeup.  */
 199       val = cond->__data.__wakeup_seq;
 200     }
 201   while (val == seq || cond->__data.__woken_seq == val);
 202
 203   /* Another thread woken up.  */
 204   ++cond->__data.__woken_seq;
 205
 206  bc_out:
 207
 208   cond->__data.__nwaiters -= 1 << COND_NWAITERS_SHIFT;
 209
 210   /* If pthread_cond_destroy was called on this varaible already,
 211      notify the pthread_cond_destroy caller all waiters have left
 212      and it can be successfully destroyed.  */
 213   if (cond->__data.__total_seq == -1ULL
 214       && cond->__data.__nwaiters < (1 << COND_NWAITERS_SHIFT))
 215     lll_futex_wake (&cond->__data.__nwaiters, 1, pshared);
 216
 217   /* We are done with the condvar.  */
 218   lll_unlock (cond->__data.__lock, pshared);
 219
 220   /* The cancellation handling is back to normal, remove the handler.  */
 221   __pthread_cleanup_pop (&buffer, 0);
 222
 223   /* Get the mutex before returning.  Not needed for PI.  */
 224 #if (defined lll_futex_wait_requeue_pi \
 225      && defined __ASSUME_REQUEUE_PI)
 226   if (pi_flag)
 227     {
 228       __pthread_mutex_cond_lock_adjust (mutex);
 229       return 0;
 230     }
 231   else
 232 #endif
 233     return __pthread_mutex_cond_lock (mutex);
 234 }
 235
 236 versioned_symbol (libpthread, __pthread_cond_wait, pthread_cond_wait,
 237                   GLIBC_2_3_2);