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+/*
+ * condvar_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) 1999,2002 Pthreads-win32 contributors
+ * 
+ *      Contact Email: rpj@ise.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:
+ * The algorithm used in this implementation is that developed by
+ * Alexander Terekhov in colaboration with Louis Thomas. The bulk
+ * of the discussion is recorded in the file README.CV, which contains
+ * several generations of both colaborators original algorithms. The final
+ * algorithm used here is the one referred to as
+ *
+ *     Algorithm 8a / IMPL_SEM,UNBLOCK_STRATEGY == UNBLOCK_ALL
+ * 
+ * presented below in pseudo-code as it appeared:
+ *
+ *
+ * given:
+ * semBlockLock - bin.semaphore
+ * semBlockQueue - semaphore
+ * mtxExternal - mutex or CS
+ * mtxUnblockLock - mutex or CS
+ * nWaitersGone - int
+ * nWaitersBlocked - int
+ * nWaitersToUnblock - int
+ * 
+ * wait( timeout ) {
+ * 
+ *   [auto: register int result          ]     // error checking omitted
+ *   [auto: register int nSignalsWasLeft ]
+ *   [auto: register int nWaitersWasGone ]
+ * 
+ *   sem_wait( semBlockLock );
+ *   nWaitersBlocked++;
+ *   sem_post( semBlockLock );
+ * 
+ *   unlock( mtxExternal );
+ *   bTimedOut = sem_wait( semBlockQueue,timeout );
+ * 
+ *   lock( mtxUnblockLock );
+ *   if ( 0 != (nSignalsWasLeft = nWaitersToUnblock) ) {
+ *     if ( bTimeout ) {                       // timeout (or canceled)
+ *       if ( 0 != nWaitersBlocked ) {
+ *         nWaitersBlocked--;
+ *       }
+ *       else {
+ *         nWaitersGone++;                     // count spurious wakeups.
+ *       }
+ *     }
+ *     if ( 0 == --nWaitersToUnblock ) {
+ *       if ( 0 != nWaitersBlocked ) {
+ *         sem_post( semBlockLock );           // open the gate.
+ *         nSignalsWasLeft = 0;                // do not open the gate
+ *                                             // below again.
+ *       }
+ *       else if ( 0 != (nWaitersWasGone = nWaitersGone) ) {
+ *         nWaitersGone = 0;
+ *       }
+ *     }
+ *   }
+ *   else if ( INT_MAX/2 == ++nWaitersGone ) { // timeout/canceled or
+ *                                             // spurious semaphore :-)
+ *     sem_wait( semBlockLock );
+ *     nWaitersBlocked -= nWaitersGone;     // something is going on here
+ *                                          //  - test of timeouts? :-)
+ *     sem_post( semBlockLock );
+ *     nWaitersGone = 0;
+ *   }
+ *   unlock( mtxUnblockLock );
+ * 
+ *   if ( 1 == nSignalsWasLeft ) {
+ *     if ( 0 != nWaitersWasGone ) {
+ *       // sem_adjust( semBlockQueue,-nWaitersWasGone );
+ *       while ( nWaitersWasGone-- ) {
+ *         sem_wait( semBlockQueue );       // better now than spurious later
+ *       }
+ *     } sem_post( semBlockLock );          // open the gate
+ *   }
+ * 
+ *   lock( mtxExternal );
+ * 
+ *   return ( bTimedOut ) ? ETIMEOUT : 0;
+ * }
+ * 
+ * signal(bAll) {
+ * 
+ *   [auto: register int result         ]
+ *   [auto: register int nSignalsToIssue]
+ * 
+ *   lock( mtxUnblockLock );
+ * 
+ *   if ( 0 != nWaitersToUnblock ) {        // the gate is closed!!!
+ *     if ( 0 == nWaitersBlocked ) {        // NO-OP
+ *       return unlock( mtxUnblockLock );
+ *     }
+ *     if (bAll) {
+ *       nWaitersToUnblock += nSignalsToIssue=nWaitersBlocked;
+ *       nWaitersBlocked = 0;
+ *     }
+ *     else {
+ *       nSignalsToIssue = 1;
+ *       nWaitersToUnblock++;
+ *       nWaitersBlocked--;
+ *     }
+ *   }
+ *   else if ( nWaitersBlocked > nWaitersGone ) { // HARMLESS RACE CONDITION!
+ *     sem_wait( semBlockLock );                  // close the gate
+ *     if ( 0 != nWaitersGone ) {
+ *       nWaitersBlocked -= nWaitersGone;
+ *       nWaitersGone = 0;
+ *     }
+ *     if (bAll) {
+ *       nSignalsToIssue = nWaitersToUnblock = nWaitersBlocked;
+ *       nWaitersBlocked = 0;
+ *     }
+ *     else {
+ *       nSignalsToIssue = nWaitersToUnblock = 1;
+ *       nWaitersBlocked--;
+ *     }
+ *   }
+ *   else { // NO-OP
+ *     return unlock( mtxUnblockLock );
+ *   }
+ * 
+ *   unlock( mtxUnblockLock );
+ *   sem_post( semBlockQueue,nSignalsToIssue );
+ *   return result;
+ * }
+ * -------------------------------------------------------------
+ *
+ */
+
+#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 ) 
+    {
+      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;
+
+}                               /* 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 '1'(TRUE) unblockAll arg means unblock ALL waiters.
+   */
+  return (ptw32_cond_unblock(cond, 1));
+
+}                               /* pthread_cond_broadcast */