sysdeps/htl/pt-cond-timedwait.c

   1 /* Wait on a condition.  Generic version.
   2    Copyright (C) 2000-2018 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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 <pthread.h>
  20
  21 #include <pt-internal.h>
  22
  23 extern int __pthread_cond_timedwait_internal (pthread_cond_t *cond,
  24                                               pthread_mutex_t *mutex,
  25                                               const struct timespec *abstime);
  26
  27 int
  28 __pthread_cond_timedwait (pthread_cond_t *cond,
  29                           pthread_mutex_t *mutex,
  30                           const struct timespec *abstime)
  31 {
  32   return __pthread_cond_timedwait_internal (cond, mutex, abstime);
  33 }
  34
  35 strong_alias (__pthread_cond_timedwait, pthread_cond_timedwait);
  36
  37 struct cancel_ctx
  38 {
  39   struct __pthread *wakeup;
  40   pthread_cond_t *cond;
  41 };
  42
  43 static void
  44 cancel_hook (void *arg)
  45 {
  46   struct cancel_ctx *ctx = arg;
  47   struct __pthread *wakeup = ctx->wakeup;
  48   pthread_cond_t *cond = ctx->cond;
  49   int unblock;
  50
  51   __pthread_spin_lock (&cond->__lock);
  52   /* The thread only needs to be awaken if it's blocking or about to block.
  53      If it was already unblocked, it's not queued any more.  */
  54   unblock = wakeup->prevp != NULL;
  55   if (unblock)
  56     __pthread_dequeue (wakeup);
  57   __pthread_spin_unlock (&cond->__lock);
  58
  59   if (unblock)
  60     __pthread_wakeup (wakeup);
  61 }
  62
  63 /* Block on condition variable COND until ABSTIME.  As a GNU
  64    extension, if ABSTIME is NULL, then wait forever.  MUTEX should be
  65    held by the calling thread.  On return, MUTEX will be held by the
  66    calling thread.  */
  67 int
  68 __pthread_cond_timedwait_internal (pthread_cond_t *cond,
  69                                    pthread_mutex_t *mutex,
  70                                    const struct timespec *abstime)
  71 {
  72   error_t err;
  73   int cancelled, oldtype, drain;
  74   clockid_t clock_id = __pthread_default_condattr.__clock;
  75
  76   if (abstime && (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000))
  77     return EINVAL;
  78
  79   struct __pthread *self = _pthread_self ();
  80   struct cancel_ctx ctx;
  81   ctx.wakeup = self;
  82   ctx.cond = cond;
  83
  84   /* Test for a pending cancellation request, switch to deferred mode for
  85      safer resource handling, and prepare the hook to call in case we're
  86      cancelled while blocking.  Once CANCEL_LOCK is released, the cancellation
  87      hook can be called by another thread at any time.  Whatever happens,
  88      this function must exit with MUTEX locked.
  89
  90      This function contains inline implementations of pthread_testcancel and
  91      pthread_setcanceltype to reduce locking overhead.  */
  92   __pthread_mutex_lock (&self->cancel_lock);
  93   cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
  94       && self->cancel_pending;
  95
  96   if (!cancelled)
  97     {
  98       self->cancel_hook = cancel_hook;
  99       self->cancel_hook_arg = &ctx;
 100       oldtype = self->cancel_type;
 101
 102       if (oldtype != PTHREAD_CANCEL_DEFERRED)
 103         self->cancel_type = PTHREAD_CANCEL_DEFERRED;
 104
 105       /* Add ourselves to the list of waiters.  This is done while setting
 106          the cancellation hook to simplify the cancellation procedure, i.e.
 107          if the thread is queued, it can be cancelled, otherwise it is
 108          already unblocked, progressing on the return path.  */
 109       __pthread_spin_lock (&cond->__lock);
 110       __pthread_enqueue (&cond->__queue, self);
 111       if (cond->__attr != NULL)
 112         clock_id = cond->__attr->__clock;
 113       __pthread_spin_unlock (&cond->__lock);
 114     }
 115   __pthread_mutex_unlock (&self->cancel_lock);
 116
 117   if (cancelled)
 118     pthread_exit (PTHREAD_CANCELED);
 119
 120   /* Release MUTEX before blocking.  */
 121   __pthread_mutex_unlock (mutex);
 122
 123   /* Block the thread.  */
 124   if (abstime != NULL)
 125     err = __pthread_timedblock (self, abstime, clock_id);
 126   else
 127     {
 128       err = 0;
 129       __pthread_block (self);
 130     }
 131
 132   __pthread_spin_lock (&cond->__lock);
 133   if (self->prevp == NULL)
 134     {
 135       /* Another thread removed us from the list of waiters, which means a
 136          wakeup message has been sent.  It was either consumed while we were
 137          blocking, or queued after we timed out and before we acquired the
 138          condition lock, in which case the message queue must be drained.  */
 139       if (!err)
 140         drain = 0;
 141       else
 142         {
 143           assert (err == ETIMEDOUT);
 144           drain = 1;
 145         }
 146     }
 147   else
 148     {
 149       /* We're still in the list of waiters.  Noone attempted to wake us up,
 150          i.e. we timed out.  */
 151       assert (err == ETIMEDOUT);
 152       __pthread_dequeue (self);
 153       drain = 0;
 154     }
 155   __pthread_spin_unlock (&cond->__lock);
 156
 157   if (drain)
 158     __pthread_block (self);
 159
 160   /* We're almost done.  Remove the unblock hook, restore the previous
 161      cancellation type, and check for a pending cancellation request.  */
 162   __pthread_mutex_lock (&self->cancel_lock);
 163   self->cancel_hook = NULL;
 164   self->cancel_hook_arg = NULL;
 165   self->cancel_type = oldtype;
 166   cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
 167       && self->cancel_pending;
 168   __pthread_mutex_unlock (&self->cancel_lock);
 169
 170   /* Reacquire MUTEX before returning/cancelling.  */
 171   __pthread_mutex_lock (mutex);
 172
 173   if (cancelled)
 174     pthread_exit (PTHREAD_CANCELED);
 175
 176   return err;
 177 }