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pthread_cond_signal.c
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pthread_cond_signal.c
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/*
* pthread_cond_signal.c
*
* Description:
* This translation unit implements condition variables and their primitives.
*
*
* --------------------------------------------------------------------------
*
* Pthreads4w - POSIX Threads for Windows
* Copyright 1998 John E. Bossom
* Copyright 1999-2018, Pthreads4w contributors
*
* Homepage: https://sourceforge.net/projects/pthreads4w/
*
* 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:
*
* https://sourceforge.net/p/pthreads4w/wiki/Contributors/
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* -------------------------------------------------------------
* Algorithm:
* See the comments at the top of pthread_cond_wait.c.
*/
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#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 = __PTW32_GET_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 = __PTW32_GET_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 */