nptl/pthread_cond_wait.c

   1 /* Copyright (C) 2003-2015 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 (cond, mutex)
 102      pthread_cond_t *cond;
 103      pthread_mutex_t *mutex;
 104 {
 105   struct _pthread_cleanup_buffer buffer;
 106   struct _condvar_cleanup_buffer cbuffer;
 107   int err;
 108   int pshared = (cond->__data.__mutex == (void *) ~0l)
 109                 ? LLL_SHARED : LLL_PRIVATE;
 110
 111 #if (defined lll_futex_wait_requeue_pi \
 112      && defined __ASSUME_REQUEUE_PI)
 113   int pi_flag = 0;
 114 #endif
 115
 116   LIBC_PROBE (cond_wait, 2, cond, mutex);
 117
 118   /* Make sure we are alone.  */
 119   lll_lock (cond->__data.__lock, pshared);
 120
 121   /* Now we can release the mutex.  */
 122   err = __pthread_mutex_unlock_usercnt (mutex, 0);
 123   if (__glibc_unlikely (err))
 124     {
 125       lll_unlock (cond->__data.__lock, pshared);
 126       return err;
 127     }
 128
 129   /* We have one new user of the condvar.  */
 130   ++cond->__data.__total_seq;
 131   ++cond->__data.__futex;
 132   cond->__data.__nwaiters += 1 << COND_NWAITERS_SHIFT;
 133
 134   /* Remember the mutex we are using here.  If there is already a
 135      different address store this is a bad user bug.  Do not store
 136      anything for pshared condvars.  */
 137   if (cond->__data.__mutex != (void *) ~0l)
 138     cond->__data.__mutex = mutex;
 139
 140   /* Prepare structure passed to cancellation handler.  */
 141   cbuffer.cond = cond;
 142   cbuffer.mutex = mutex;
 143
 144   /* Before we block we enable cancellation.  Therefore we have to
 145      install a cancellation handler.  */
 146   __pthread_cleanup_push (&buffer, __condvar_cleanup, &cbuffer);
 147
 148   /* The current values of the wakeup counter.  The "woken" counter
 149      must exceed this value.  */
 150   unsigned long long int val;
 151   unsigned long long int seq;
 152   val = seq = cond->__data.__wakeup_seq;
 153   /* Remember the broadcast counter.  */
 154   cbuffer.bc_seq = cond->__data.__broadcast_seq;
 155
 156   do
 157     {
 158       unsigned int futex_val = cond->__data.__futex;
 159       /* Prepare to wait.  Release the condvar futex.  */
 160       lll_unlock (cond->__data.__lock, pshared);
 161
 162       /* Enable asynchronous cancellation.  Required by the standard.  */
 163       cbuffer.oldtype = __pthread_enable_asynccancel ();
 164
 165 #if (defined lll_futex_wait_requeue_pi \
 166      && defined __ASSUME_REQUEUE_PI)
 167       /* If pi_flag remained 1 then it means that we had the lock and the mutex
 168          but a spurious waker raced ahead of us.  Give back the mutex before
 169          going into wait again.  */
 170       if (pi_flag)
 171         {
 172           __pthread_mutex_cond_lock_adjust (mutex);
 173           __pthread_mutex_unlock_usercnt (mutex, 0);
 174         }
 175       pi_flag = USE_REQUEUE_PI (mutex);
 176
 177       if (pi_flag)
 178         {
 179           err = lll_futex_wait_requeue_pi (&cond->__data.__futex,
 180                                            futex_val, &mutex->__data.__lock,
 181                                            pshared);
 182
 183           pi_flag = (err == 0);
 184         }
 185       else
 186 #endif
 187           /* Wait until woken by signal or broadcast.  */
 188         lll_futex_wait (&cond->__data.__futex, futex_val, pshared);
 189
 190       /* Disable asynchronous cancellation.  */
 191       __pthread_disable_asynccancel (cbuffer.oldtype);
 192
 193       /* We are going to look at shared data again, so get the lock.  */
 194       lll_lock (cond->__data.__lock, pshared);
 195
 196       /* If a broadcast happened, we are done.  */
 197       if (cbuffer.bc_seq != cond->__data.__broadcast_seq)
 198         goto bc_out;
 199
 200       /* Check whether we are eligible for wakeup.  */
 201       val = cond->__data.__wakeup_seq;
 202     }
 203   while (val == seq || cond->__data.__woken_seq == val);
 204
 205   /* Another thread woken up.  */
 206   ++cond->__data.__woken_seq;
 207
 208  bc_out:
 209
 210   cond->__data.__nwaiters -= 1 << COND_NWAITERS_SHIFT;
 211
 212   /* If pthread_cond_destroy was called on this varaible already,
 213      notify the pthread_cond_destroy caller all waiters have left
 214      and it can be successfully destroyed.  */
 215   if (cond->__data.__total_seq == -1ULL
 216       && cond->__data.__nwaiters < (1 << COND_NWAITERS_SHIFT))
 217     lll_futex_wake (&cond->__data.__nwaiters, 1, pshared);
 218
 219   /* We are done with the condvar.  */
 220   lll_unlock (cond->__data.__lock, pshared);
 221
 222   /* The cancellation handling is back to normal, remove the handler.  */
 223   __pthread_cleanup_pop (&buffer, 0);
 224
 225   /* Get the mutex before returning.  Not needed for PI.  */
 226 #if (defined lll_futex_wait_requeue_pi \
 227      && defined __ASSUME_REQUEUE_PI)
 228   if (pi_flag)
 229     {
 230       __pthread_mutex_cond_lock_adjust (mutex);
 231       return 0;
 232     }
 233   else
 234 #endif
 235     return __pthread_mutex_cond_lock (mutex);
 236 }
 237
 238 versioned_symbol (libpthread, __pthread_cond_wait, pthread_cond_wait,
 239                   GLIBC_2_3_2);