pthread_cond_signal.c

/*
 * pthread_cond_signal.c
 *
 * Description:
 * This translation unit implements condition variables and their primitives.
 *
 *
 * --------------------------------------------------------------------------
 *
 *      Pthreads-embedded (PTE) - POSIX Threads Library for embedded systems
 *      Copyright(C) 2008 Jason Schmidlapp
 *
 *      Contact Email: jschmidlapp@users.sourceforge.net
 *
 *
 *      Based upon 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 original list of contributors to the Pthreads-win32 project
 *      is contained in the file CONTRIBUTORS.ptw32 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 int
pte_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 (sem_wait_nocancel (&(cv->semBlockLock)) != 0)
      if (sem_wait (&(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;

}				/* pte_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 (pte_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 (pte_cond_unblock (cond, PTE_TRUE));

}				/* pthread_cond_broadcast */