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+/*
+ * 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) 1999,2002 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 */
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