xref: /freebsd-11-stable/sys/contrib/ck/src/ck_barrier_centralized.c

/*
 * Copyright 2011-2015 Samy Al Bahra.
 * Copyright 2011 David Joseph.
 * All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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 OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED 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.
 */

#include <ck_barrier.h>
#include <ck_pr.h>

void
ck_barrier_centralized(struct ck_barrier_centralized *barrier,
    struct ck_barrier_centralized_state *state,
    unsigned int n_threads)
{
	unsigned int sense, value;

	/*
	 * Every execution context has a sense associated with it.
	 * This sense is reversed when the barrier is entered. Every
	 * thread will spin on the global sense until the last thread
	 * reverses it.
	 */
	sense = state->sense = ~state->sense;
	value = ck_pr_faa_uint(&barrier->value, 1);
	if (value == n_threads - 1) {
		ck_pr_store_uint(&barrier->value, 0);
		ck_pr_fence_memory();
		ck_pr_store_uint(&barrier->sense, sense);
		return;
	}

	ck_pr_fence_atomic_load();
	while (sense != ck_pr_load_uint(&barrier->sense))
		ck_pr_stall();

	ck_pr_fence_acquire();
	return;
}