xref: /xsrc/external/mit/libxshmfence/dist/src/xshmfence_futex.c

/*
 * Copyright © 2013 Keith Packard
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting documentation, and
 * that the name of the copyright holders not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  The copyright holders make no representations
 * about the suitability of this software for any purpose.  It is provided "as
 * is" without express or implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 */

#if HAVE_CONFIG_H
#include "config.h"
#endif

#include "xshmfenceint.h"

/**
 * xshmfence_trigger:
 * @f: An X fence
 *
 * Set @f to triggered, waking all waiters.
 *
 * Return value: 0 on success and -1 on error (in which case, errno
 * will be set as appropriate).
 **/
int
xshmfence_trigger(struct xshmfence *f)
{
	if (__sync_val_compare_and_swap(&f->v, 0, 1) == -1) {
		atomic_store(&f->v, 1);
		if (futex_wake(&f->v) < 0)
			return -1;
	}
	return 0;
}

/**
 * xshmfence_await:
 * @f: An X fence
 *
 * Wait for @f to be triggered. If @f is already triggered, this
 * function returns immediately.
 *
 * Return value: 0 on success and -1 on error (in which case, errno
 * will be set as appropriate).
 **/
int
xshmfence_await(struct xshmfence *f)
{
	while (__sync_val_compare_and_swap(&f->v, 0, -1) != 1) {
		if (futex_wait(&f->v, -1)) {
			if (errno != EWOULDBLOCK)
				return -1;
		}
	}
	return 0;
}

/**
 * xshmfence_query:
 * @f: An X fence
 *
 * Return value: 1 if @f is triggered, else returns 0.
 **/
int
xshmfence_query(struct xshmfence *f)
{
	return atomic_fetch(&f->v) == 1;
}

/**
 * xshmfence_reset:
 * @f: An X fence
 *
 * Reset @f to untriggered. If @f is already untriggered,
 * this function has no effect.
 **/
void
xshmfence_reset(struct xshmfence *f)
{
	__sync_bool_compare_and_swap(&f->v, 1, 0);
}