sysdeps/htl/pt-cond-timedwait.c

   1 /* Wait on a condition.  Generic version.
   2    Copyright (C) 2000-2024 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <pthread.h>
  20
  21 #include <pt-internal.h>
  22 #include <pthreadP.h>
  23 #include <time.h>
  24
  25 extern int __pthread_cond_timedwait_internal (pthread_cond_t *cond,
  26                                               pthread_mutex_t *mutex,
  27                                               clockid_t clockid,
  28                                               const struct timespec *abstime);
  29
  30 int
  31 __pthread_cond_timedwait (pthread_cond_t *cond,
  32                           pthread_mutex_t *mutex,
  33                           const struct timespec *abstime)
  34 {
  35   return __pthread_cond_timedwait_internal (cond, mutex, -1, abstime);
  36 }
  37
  38 weak_alias (__pthread_cond_timedwait, pthread_cond_timedwait);
  39
  40 int
  41 __pthread_cond_clockwait (pthread_cond_t *cond,
  42                           pthread_mutex_t *mutex,
  43                           clockid_t clockid,
  44                           const struct timespec *abstime)
  45 {
  46   return __pthread_cond_timedwait_internal (cond, mutex, clockid, abstime);
  47 }
  48
  49 weak_alias (__pthread_cond_clockwait, pthread_cond_clockwait);
  50
  51 struct cancel_ctx
  52 {
  53   struct __pthread *wakeup;
  54   pthread_cond_t *cond;
  55 };
  56
  57 static void
  58 cancel_hook (void *arg)
  59 {
  60   struct cancel_ctx *ctx = arg;
  61   struct __pthread *wakeup = ctx->wakeup;
  62   pthread_cond_t *cond = ctx->cond;
  63   int unblock;
  64
  65   __pthread_spin_wait (&cond->__lock);
  66   /* The thread only needs to be awaken if it's blocking or about to block.
  67      If it was already unblocked, it's not queued any more.  */
  68   unblock = wakeup->prevp != NULL;
  69   if (unblock)
  70     __pthread_dequeue (wakeup);
  71   __pthread_spin_unlock (&cond->__lock);
  72
  73   if (unblock)
  74     __pthread_wakeup (wakeup);
  75 }
  76
  77 /* Block on condition variable COND until ABSTIME.  As a GNU
  78    extension, if ABSTIME is NULL, then wait forever.  MUTEX should be
  79    held by the calling thread.  On return, MUTEX will be held by the
  80    calling thread.  */
  81 int
  82 __pthread_cond_timedwait_internal (pthread_cond_t *cond,
  83                                    pthread_mutex_t *mutex,
  84                                    clockid_t clockid,
  85                                    const struct timespec *abstime)
  86 {
  87   error_t err;
  88   int cancelled, oldtype, drain;
  89   clockid_t clock_id;
  90
  91   if (clockid != -1)
  92     clock_id = clockid;
  93   else
  94     clock_id = __pthread_default_condattr.__clock;
  95
  96   if (abstime && ! valid_nanoseconds (abstime->tv_nsec))
  97     return EINVAL;
  98
  99   err = __pthread_mutex_checklocked (mutex);
 100   if (err)
 101     return err;
 102
 103   struct __pthread *self = _pthread_self ();
 104   struct cancel_ctx ctx;
 105   ctx.wakeup = self;
 106   ctx.cond = cond;
 107
 108   /* Test for a pending cancellation request, switch to deferred mode for
 109      safer resource handling, and prepare the hook to call in case we're
 110      cancelled while blocking.  Once CANCEL_LOCK is released, the cancellation
 111      hook can be called by another thread at any time.  Whatever happens,
 112      this function must exit with MUTEX locked.
 113
 114      This function contains inline implementations of pthread_testcancel and
 115      pthread_setcanceltype to reduce locking overhead.  */
 116   __pthread_mutex_lock (&self->cancel_lock);
 117   cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
 118       && self->cancel_pending;
 119
 120   if (cancelled)
 121     {
 122       __pthread_mutex_unlock (&self->cancel_lock);
 123       __pthread_exit (PTHREAD_CANCELED);
 124     }
 125
 126   self->cancel_hook = cancel_hook;
 127   self->cancel_hook_arg = &ctx;
 128   oldtype = self->cancel_type;
 129
 130   if (oldtype != PTHREAD_CANCEL_DEFERRED)
 131     self->cancel_type = PTHREAD_CANCEL_DEFERRED;
 132
 133   /* Add ourselves to the list of waiters.  This is done while setting
 134      the cancellation hook to simplify the cancellation procedure, i.e.
 135      if the thread is queued, it can be cancelled, otherwise it is
 136      already unblocked, progressing on the return path.  */
 137   __pthread_spin_wait (&cond->__lock);
 138   __pthread_enqueue (&cond->__queue, self);
 139   if (cond->__attr != NULL && clockid == -1)
 140     clock_id = cond->__attr->__clock;
 141   __pthread_spin_unlock (&cond->__lock);
 142
 143   __pthread_mutex_unlock (&self->cancel_lock);
 144
 145   /* Increase the waiter reference count.  Relaxed MO is sufficient because
 146      we only need to synchronize when decrementing the reference count.
 147      We however need to have the mutex held to prevent concurrency with
 148      a pthread_cond_destroy.  */
 149   atomic_fetch_add_relaxed (&cond->__wrefs, 2);
 150
 151   /* Release MUTEX before blocking.  */
 152   __pthread_mutex_unlock (mutex);
 153
 154   /* Block the thread.  */
 155   if (abstime != NULL)
 156     err = __pthread_timedblock (self, abstime, clock_id);
 157   else
 158     {
 159       err = 0;
 160       __pthread_block (self);
 161     }
 162
 163   __pthread_spin_wait (&cond->__lock);
 164   if (self->prevp == NULL)
 165     {
 166       /* Another thread removed us from the list of waiters, which means a
 167          wakeup message has been sent.  It was either consumed while we were
 168          blocking, or queued after we timed out and before we acquired the
 169          condition lock, in which case the message queue must be drained.  */
 170       if (!err)
 171         drain = 0;
 172       else
 173         {
 174           assert (err == ETIMEDOUT);
 175           drain = 1;
 176         }
 177     }
 178   else
 179     {
 180       /* We're still in the list of waiters.  No one attempted to wake us up,
 181          i.e. we timed out.  */
 182       assert (err == ETIMEDOUT);
 183       __pthread_dequeue (self);
 184       drain = 0;
 185     }
 186   __pthread_spin_unlock (&cond->__lock);
 187
 188   /* If destruction is pending (i.e., the wake-request flag is nonzero) and we
 189      are the last waiter (prior value of __wrefs was 1 << 1), then wake any
 190      threads waiting in pthread_cond_destroy.  Release MO to synchronize with
 191      these threads.  Don't bother clearing the wake-up request flag.  */
 192   if ((atomic_fetch_add_release (&cond->__wrefs, -2)) == 3)
 193     __gsync_wake (__mach_task_self (), (vm_offset_t) &cond->__wrefs, 0, 0);
 194
 195   if (drain)
 196     __pthread_block (self);
 197
 198   /* We're almost done.  Remove the unblock hook, restore the previous
 199      cancellation type, and check for a pending cancellation request.  */
 200   __pthread_mutex_lock (&self->cancel_lock);
 201   self->cancel_hook = NULL;
 202   self->cancel_hook_arg = NULL;
 203   self->cancel_type = oldtype;
 204   cancelled = (self->cancel_state == PTHREAD_CANCEL_ENABLE)
 205       && self->cancel_pending;
 206   __pthread_mutex_unlock (&self->cancel_lock);
 207
 208   /* Reacquire MUTEX before returning/cancelling.  */
 209   __pthread_mutex_lock (mutex);
 210
 211   if (cancelled)
 212     __pthread_exit (PTHREAD_CANCELED);
 213
 214   return err;
 215 }