pthread_cond_signal.c 6.65 KB
Newer Older
Jason Schmidlapp's avatar
Jason Schmidlapp committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238
/*
 * 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 */