1 /*
2  * Copyright 2011-2015 Samy Al Bahra.
3  * Copyright 2011 David Joseph.
4  * All rights reserved.
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions
8  * are met:
9  * 1. Redistributions of source code must retain the above copyright
10  *    notice, this list of conditions and the following disclaimer.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in the
13  *    documentation and/or other materials provided with the distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25  * SUCH DAMAGE.
26  */
27 
28 #include <ck_barrier.h>
29 #include <ck_pr.h>
30 
31 void
32 ck_barrier_centralized(struct ck_barrier_centralized *barrier,
33     struct ck_barrier_centralized_state *state,
34     unsigned int n_threads)
35 {
36 	unsigned int sense, value;
37 
38 	/*
39 	 * Every execution context has a sense associated with it.
40 	 * This sense is reversed when the barrier is entered. Every
41 	 * thread will spin on the global sense until the last thread
42 	 * reverses it.
43 	 */
44 	sense = state->sense = ~state->sense;
45 	value = ck_pr_faa_uint(&barrier->value, 1);
46 	if (value == n_threads - 1) {
47 		ck_pr_store_uint(&barrier->value, 0);
48 		ck_pr_fence_memory();
49 		ck_pr_store_uint(&barrier->sense, sense);
50 		return;
51 	}
52 
53 	ck_pr_fence_atomic_load();
54 	while (sense != ck_pr_load_uint(&barrier->sense))
55 		ck_pr_stall();
56 
57 	ck_pr_fence_acquire();
58 	return;
59 }
60