/********************************************************************************
* sched/pthread_barrierwait.c
*
* Copyright (C) 2007, 2009 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
********************************************************************************/
/********************************************************************************
* Included Files
********************************************************************************/
#include <nuttx/config.h>
#include <pthread.h>
#include <semaphore.h>
#include <sched.h>
#include <errno.h>
#include <debug.h>
/********************************************************************************
* Definitions
********************************************************************************/
/********************************************************************************
* Private Type Declarations
********************************************************************************/
/********************************************************************************
* Global Variables
********************************************************************************/
/********************************************************************************
* Private Variables
********************************************************************************/
/********************************************************************************
* Private Function Prototypes
********************************************************************************/
/********************************************************************************
* Public Functions
********************************************************************************/
/********************************************************************************
* Name: pthread_barrier_wait
*
* Description:
* The pthread_barrier_wait() function synchronizse participating threads at
* the barrier referenced by 'barrier'. The calling thread is blocked until
* the required number of threads have called pthread_barrier_wait() specifying
* the same 'barrier'. When the required number of threads have called
* pthread_barrier_wait() specifying the 'barrier', the constant
* PTHREAD_BARRIER_SERIAL_THREAD will be returned to one unspecified thread
* and zero will be returned to each of the remaining threads. At this point,
* the barrier will be reset to the state it had as a result of the most recent
* pthread_barrier_init() function that referenced it.
*
* The constant PTHREAD_BARRIER_SERIAL_THREAD is defined in pthread.h and its
* value must be distinct from any other value returned by pthread_barrier_wait().
*
* The results are undefined if this function is called with an uninitialized
* barrier.
*
* If a signal is delivered to a thread blocked on a barrier, upon return from
* the signal handler the thread will resume waiting at the barrier if the barrier
* wait has not completed; otherwise, the thread will continue as normal from
* the completed barrier wait. Until the thread in the signal handler returns
* from it, it is unspecified whether other threads may proceed past the barrier
* once they have all reached it.
*
* A thread that has blocked on a barrier will not prevent any unblocked thread
* that is eligible to use the same processing resources from eventually making
* forward progress in its execution. Eligibility for processing resources will
* be determined by the scheduling policy.
*
* Parameters:
* barrier - the barrier to wait on
*
* Return Value:
* 0 (OK) on success or EINVAL if the barrier is not valid.
*
* Assumptions:
*
********************************************************************************/
int pthread_barrier_wait(FAR pthread_barrier_t *barrier)
{
int semcount;
int ret = OK;
if (!barrier)
{
return EINVAL;
}
/* Disable pre-emption throughout the following */
sched_lock();
/* Find out how many threads are already waiting at the barrier */
ret = sem_getvalue(&barrier->sem, &semcount);
if (ret != OK)
{
sched_unlock();
return EINVAL;
}
/* If the number of waiters would be equal to the count, then we are done */
if (1 - semcount >= barrier->count)
{
/* Free all of the waiting threads */
while (semcount < 0)
{
(void)sem_post(&barrier->sem);
(void)sem_getvalue(&barrier->sem, &semcount);
}
/* Then return PTHREAD_BARRIER_SERIAL_THREAD to the final thread */
sched_unlock();
return PTHREAD_BARRIER_SERIAL_THREAD;
}
else
{
/* Otherwise, this thread must wait as well */
while (sem_wait(&barrier->sem) != OK)
{
/* If the thread is awakened by a signal, just continue to wait */
int errornumber = get_errno();
if (errornumber != EINTR)
{
/* If it is awakened by some other error, then there is a
* problem
*/
sched_unlock();
return errornumber;
}
}
/* We will only get here when we are one of the N-1 threads that were
* waiting for the final thread at the barrier. We just need to return
* zero.
*/
sched_unlock();
return 0;
}
}
