pthread_cond_signal.c

/*
 * pthread_cond_signal.c
 *
 * Description:
 * This translation unit implements condition variables and their primitives.
 *
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads-win32 - POSIX Threads Library for Win32
 *      Copyright(C) 1998 John E. Bossom
 *      Copyright(C) 1999,2005 Pthreads-win32 contributors
 * 
 *      Contact Email: rpj@callisto.canberra.edu.au
 * 
 *      The current list of contributors is contained
 *      in the file CONTRIBUTORS included with the source
 *      code distribution. The list can also be seen at the
 *      following World Wide Web location:
 *      http://sources.redhat.com/pthreads-win32/contributors.html
 * 
 *      This library is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU Lesser General Public
 *      License as published by the Free Software Foundation; either
 *      version 2 of the License, or (at your option) any later version.
 * 
 *      This library is distributed in the hope that it will be useful,
 *      but WITHOUT ANY WARRANTY; without even the implied warranty of
 *      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *      Lesser General Public License for more details.
 * 
 *      You should have received a copy of the GNU Lesser General Public
 *      License along with this library in the file COPYING.LIB;
 *      if not, write to the Free Software Foundation, Inc.,
 *      59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 *
 * -------------------------------------------------------------
 * Algorithm:
 * See the comments at the top of pthread_cond_wait.c.
 */

#include "pthread.h"
#include "implement.h"

static INLINE int
ptw32_cond_unblock (pthread_cond_t * cond, int unblockAll)
     /*
      * Notes.
      *
      * Does not use the external mutex for synchronisation,
      * therefore semBlockLock is needed.
      * mtxUnblockLock is for LEVEL-2 synch. LEVEL-2 is the
      * state where the external mutex is not necessarily locked by
      * any thread, ie. between cond_wait unlocking and re-acquiring
      * the lock after having been signaled or a timeout or
      * cancellation.
      *
      * Uses the following CV elements:
      *   nWaitersBlocked
      *   nWaitersToUnblock
      *   nWaitersGone
      *   mtxUnblockLock
      *   semBlockLock
      *   semBlockQueue
      */
{
  int result;
  pthread_cond_t cv;
  int nSignalsToIssue;

  if (cond == NULL || *cond == NULL)
    {
      return EINVAL;
    }

  cv = *cond;

  /*
   * No-op if the CV is static and hasn't been initialised yet.
   * Assuming that any race condition is harmless.
   */
  if (cv == PTHREAD_COND_INITIALIZER)
    {
      return 0;
    }

  if ((result = pthread_mutex_lock (&(cv->mtxUnblockLock))) != 0)
    {
      return result;
    }

  if (0 != cv->nWaitersToUnblock)
    {
      if (0 == cv->nWaitersBlocked)
	{
	  return pthread_mutex_unlock (&(cv->mtxUnblockLock));
	}
      if (unblockAll)
	{
	  cv->nWaitersToUnblock += (nSignalsToIssue = cv->nWaitersBlocked);
	  cv->nWaitersBlocked = 0;
	}
      else
	{
	  nSignalsToIssue = 1;
	  cv->nWaitersToUnblock++;
	  cv->nWaitersBlocked--;
	}
    }
  else if (cv->nWaitersBlocked > cv->nWaitersGone)
    {
      /* Use the non-cancellable version of sem_wait() */
      if (ptw32_semwait (&(cv->semBlockLock)) != 0)
	{
	  result = errno;
	  (void) pthread_mutex_unlock (&(cv->mtxUnblockLock));
	  return result;
	}
      if (0 != cv->nWaitersGone)
	{
	  cv->nWaitersBlocked -= cv->nWaitersGone;
	  cv->nWaitersGone = 0;
	}
      if (unblockAll)
	{
	  nSignalsToIssue = cv->nWaitersToUnblock = cv->nWaitersBlocked;
	  cv->nWaitersBlocked = 0;
	}
      else
	{
	  nSignalsToIssue = cv->nWaitersToUnblock = 1;
	  cv->nWaitersBlocked--;
	}
    }
  else
    {
      return pthread_mutex_unlock (&(cv->mtxUnblockLock));
    }

  if ((result = pthread_mutex_unlock (&(cv->mtxUnblockLock))) == 0)
    {
      if (sem_post_multiple (&(cv->semBlockQueue), nSignalsToIssue) != 0)
	{
	  result = errno;
	}
    }

  return result;

}				/* ptw32_cond_unblock */

int
pthread_cond_signal (pthread_cond_t * cond)
     /*
      * ------------------------------------------------------
      * DOCPUBLIC
      *      This function signals a condition variable, waking
      *      one waiting thread.
      *      If SCHED_FIFO or SCHED_RR policy threads are waiting
      *      the highest priority waiter is awakened; otherwise,
      *      an unspecified waiter is awakened.
      *
      * PARAMETERS
      *      cond
      *              pointer to an instance of pthread_cond_t
      *
      *
      * DESCRIPTION
      *      This function signals a condition variable, waking
      *      one waiting thread.
      *      If SCHED_FIFO or SCHED_RR policy threads are waiting
      *      the highest priority waiter is awakened; otherwise,
      *      an unspecified waiter is awakened.
      *
      *      NOTES:
      *
      *      1)      Use when any waiter can respond and only one need
      *              respond (all waiters being equal).
      *
      * RESULTS
      *              0               successfully signaled condition,
      *              EINVAL          'cond' is invalid,
      *
      * ------------------------------------------------------
      */
{
  /*
   * The '0'(FALSE) unblockAll arg means unblock ONE waiter.
   */
  return (ptw32_cond_unblock (cond, 0));

}				/* pthread_cond_signal */

int
pthread_cond_broadcast (pthread_cond_t * cond)
     /*
      * ------------------------------------------------------
      * DOCPUBLIC
      *      This function broadcasts the condition variable,
      *      waking all current waiters.
      *
      * PARAMETERS
      *      cond
      *              pointer to an instance of pthread_cond_t
      *
      *
      * DESCRIPTION
      *      This function signals a condition variable, waking
      *      all waiting threads.
      *
      *      NOTES:
      *
      *      1)      Use when more than one waiter may respond to
      *              predicate change or if any waiting thread may
      *              not be able to respond
      *
      * RESULTS
      *              0               successfully signalled condition to all
      *                              waiting threads,
      *              EINVAL          'cond' is invalid
      *              ENOSPC          a required resource has been exhausted,
      *
      * ------------------------------------------------------
      */
{
  /*
   * The TRUE unblockAll arg means unblock ALL waiters.
   */
  return (ptw32_cond_unblock (cond, PTW32_TRUE));

}				/* pthread_cond_broadcast */