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 #include <pthreadP.h>
  23
  24 extern int __pthread_cond_timedwait_internal (pthread_cond_t *cond,
  25                                               pthread_mutex_t *mutex,
  26                                               const struct timespec *abstime);
  27
  28 int
  29 __pthread_cond_timedwait (pthread_cond_t *cond,
  30                           pthread_mutex_t *mutex,
  31                           const struct timespec *abstime)
  32 {
  33   return __pthread_cond_timedwait_internal (cond, mutex, abstime);
  34 }
  35
  36 strong_alias (__pthread_cond_timedwait, pthread_cond_timedwait);
  37
  38 struct cancel_ctx
  39 {
  40   struct __pthread *wakeup;
  41   pthread_cond_t *cond;
  42 };
  43
  44 static void
  45 cancel_hook (void *arg)
  46 {
  47   struct cancel_ctx *ctx = arg;
  48   struct __pthread *wakeup = ctx->wakeup;
  49   pthread_cond_t *cond = ctx->cond;
  50   int unblock;
  51
  52   __pthread_spin_lock (&cond->__lock);
  53   /* The thread only needs to be awaken if it's blocking or about to block.
  54      If it was already unblocked, it's not queued any more.  */
  55   unblock = wakeup->prevp != NULL;
  56   if (unblock)
  57     __pthread_dequeue (wakeup);
  58   __pthread_spin_unlock (&cond->__lock);
  59
  60   if (unblock)
  61     __pthread_wakeup (wakeup);
  62 }
  63
  64 /* Block on condition variable COND until ABSTIME.  As a GNU
  65    extension, if ABSTIME is NULL, then wait forever.  MUTEX should be
  66    held by the calling thread.  On return, MUTEX will be held by the
  67    calling thread.  */
  68 int
  69 __pthread_cond_timedwait_internal (pthread_cond_t *cond,
  70                                    pthread_mutex_t *mutex,
  71                                    const struct timespec *abstime)
  72 {
  73   error_t err;
  74   int cancelled, oldtype, drain;
  75   clockid_t clock_id = __pthread_default_condattr.__clock;
  76
  77   if (abstime && (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000))
  78     return EINVAL;
  79
  80   struct __pthread *self = _pthread_self ();
  81   struct cancel_ctx ctx;
  82   ctx.wakeup = self;
  83   ctx.cond = cond;
  84
  85   /* Test for a pending cancellation request, switch to deferred mode for
  86      safer resource handling, and prepare the hook to call in case we're
  87      cancelled while blocking.  Once CANCEL_LOCK is released, the cancellation
  88      hook can be called by another thread at any time.  Whatever happens,
  89      this function must exit with MUTEX locked.
  90
  91      This function contains inline implementations of pthread_testcancel and
  92      pthread_setcanceltype to reduce locking overhead.  */
  93   __pthread_mutex_lock (&self->cancel_lock);
  94   cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
  95       && self->cancel_pending;
  96
  97   if (!cancelled)
  98     {
  99       self->cancel_hook = cancel_hook;
 100       self->cancel_hook_arg = &ctx;
 101       oldtype = self->cancel_type;
 102
 103       if (oldtype != PTHREAD_CANCEL_DEFERRED)
 104         self->cancel_type = PTHREAD_CANCEL_DEFERRED;
 105
 106       /* Add ourselves to the list of waiters.  This is done while setting
 107          the cancellation hook to simplify the cancellation procedure, i.e.
 108          if the thread is queued, it can be cancelled, otherwise it is
 109          already unblocked, progressing on the return path.  */
 110       __pthread_spin_lock (&cond->__lock);
 111       __pthread_enqueue (&cond->__queue, self);
 112       if (cond->__attr != NULL)
 113         clock_id = cond->__attr->__clock;
 114       __pthread_spin_unlock (&cond->__lock);
 115     }
 116   __pthread_mutex_unlock (&self->cancel_lock);
 117
 118   if (cancelled)
 119     __pthread_exit (PTHREAD_CANCELED);
 120
 121   /* Release MUTEX before blocking.  */
 122   __pthread_mutex_unlock (mutex);
 123
 124   /* Block the thread.  */
 125   if (abstime != NULL)
 126     err = __pthread_timedblock (self, abstime, clock_id);
 127   else
 128     {
 129       err = 0;
 130       __pthread_block (self);
 131     }
 132
 133   __pthread_spin_lock (&cond->__lock);
 134   if (self->prevp == NULL)
 135     {
 136       /* Another thread removed us from the list of waiters, which means a
 137          wakeup message has been sent.  It was either consumed while we were
 138          blocking, or queued after we timed out and before we acquired the
 139          condition lock, in which case the message queue must be drained.  */
 140       if (!err)
 141         drain = 0;
 142       else
 143         {
 144           assert (err == ETIMEDOUT);
 145           drain = 1;
 146         }
 147     }
 148   else
 149     {
 150       /* We're still in the list of waiters.  Noone attempted to wake us up,
 151          i.e. we timed out.  */
 152       assert (err == ETIMEDOUT);
 153       __pthread_dequeue (self);
 154       drain = 0;
 155     }
 156   __pthread_spin_unlock (&cond->__lock);
 157
 158   if (drain)
 159     __pthread_block (self);
 160
 161   /* We're almost done.  Remove the unblock hook, restore the previous
 162      cancellation type, and check for a pending cancellation request.  */
 163   __pthread_mutex_lock (&self->cancel_lock);
 164   self->cancel_hook = NULL;
 165   self->cancel_hook_arg = NULL;
 166   self->cancel_type = oldtype;
 167   cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
 168       && self->cancel_pending;
 169   __pthread_mutex_unlock (&self->cancel_lock);
 170
 171   /* Reacquire MUTEX before returning/cancelling.  */
 172   __pthread_mutex_lock (mutex);
 173
 174   if (cancelled)
 175     __pthread_exit (PTHREAD_CANCELED);
 176
 177   return err;
 178 }