[d64a94]: pthread_cond_signal.c  Maximize  Restore  History

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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) 1999,2005 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:
* 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)
{
/* 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 */