/*
* barrier.c
*
* This file implements the "barrier" synchronization construct.
*
* A barrier causes threads to wait until a set of threads has
* all "reached" the barrier. The number of threads required is
* set when the barrier is initialized, and cannot be changed
* except by reinitializing.
*
* The barrier_init() and barrier_destroy() functions,
* respectively, allow you to initialize and destroy the
* barrier.
*
* The barrier_wait() function allows a thread to wait for a
* barrier to be completed. One thread (the one that happens to
* arrive last) will return from barrier_wait() with the status
* -1 on success -- others will return with 0. The special
* status makes it easy for the calling code to cause one thread
* to do something in a serial region before entering another
* parallel section of code.
*/

#include <pthread.h>
// #include "errors.h"
#include "barrier.h"

/*
* Initialize a barrier for use.
*/
int barrier_init (barrier_t *barrier, int count)
{
	int status;
	barrier->threshold = barrier->counter = count;
	barrier->cycle = 0;
	status = pthread_mutex_init (&barrier->mutex, NULL);
	if (status != 0)
			return status;
	status = pthread_cond_init (&barrier->cv, NULL);
	if (status != 0) {
			pthread_mutex_destroy (&barrier->mutex);
			return status;
	}
	barrier->valid = BARRIER_VALID;
	return 0;
}

/*
* Destroy a barrier when done using it.
*/
int barrier_destroy (barrier_t *barrier)
{
	int status, status2;

	if (barrier->valid != BARRIER_VALID)
			return EINVAL;
	status = pthread_mutex_lock (&barrier->mutex);
	if (status != 0)
			return status;
	/*
		* Check whether any threads are known to be waiting; report
		* "BUSY" if so.
		*/
	if (barrier->counter != barrier->threshold) {
			pthread_mutex_unlock (&barrier->mutex);
			return EBUSY;
	}
	barrier->valid = 0;
	status = pthread_mutex_unlock (&barrier->mutex);
	if (status != 0)
			return status;
	/*
		* If unable to destroy either 1003.1c synchronization
		* object, return the error status.
		*/
	status = pthread_mutex_destroy (&barrier->mutex);
	status2 = pthread_cond_destroy (&barrier->cv);
	return (status == 0 ? status : status2);
}

/*
* Wait for all members of a barrier to reach the barrier. When
* the count (of remaining members) reaches 0, broadcast to wake
* all threads waiting.
*/

int barrier_wait (barrier_t *barrier)
{
	int status, cancel, tmp, cycle;
	if (barrier->valid != BARRIER_VALID)
		return EINVAL;
	status = pthread_mutex_lock (&barrier->mutex);
	if (status != 0)
		return status;
	cycle = barrier->cycle;     /* Remember which cycle we’re on */
	if (--barrier->counter == 0) {
		barrier->cycle = !barrier->cycle;
		barrier->counter = barrier->threshold;
		status = pthread_cond_broadcast (&barrier->cv);
		/*
		* The last thread into the barrier will return status
		* -1 rather than 0, so that it can be used to perform
		* some special serial code following the barrier.
		*/
		if (status == 0)
			status = -1;
	} else {
		/*
		* Wait with cancellation disabled, because barrier_wait
		* should not be a cancellation point.
		*/
		pthread_setcancelstate (PTHREAD_CANCEL_DISABLE, &cancel);
		/*
		* Wait until the barrier’s cycle changes, which means
		* that it has been broadcast, and we don’t want to wait
		* anymore.
		*/
		while (cycle == barrier->cycle) {
			status = pthread_cond_wait (
					&barrier->cv, &barrier->mutex);
			if (status != 0) break;
		}
		pthread_setcancelstate (cancel, &tmp);
	}
	/*
	* Ignore an error in unlocking. It shouldn’t happen, and
	* reporting it here would be misleading -- the barrier wait
	* completed, after all, whereas returning, for example,
	* EINVAL would imply the wait had failed. The next attempt
	* to use the barrier *will* return an error, or hang, due
	* to whatever happened to the mutex.
	*/
	pthread_mutex_unlock (&barrier->mutex);
	return status;            /* error, -1 for waker, or 0 */
}