1/* Copyright (c) 2013, Ben Noordhuis <info@bnoordhuis.nl>
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
10 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
12 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
13 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
14 */
15
16#ifndef UV_SPINLOCK_H_
17#define UV_SPINLOCK_H_
18
19#include "internal.h" /* ACCESS_ONCE, UV_UNUSED */
20#include "atomic-ops.h"
21
22#define UV_SPINLOCK_INITIALIZER { 0 }
23
24typedef struct {
25 int lock;
26} uv_spinlock_t;
27
28UV_UNUSED(static void uv_spinlock_init(uv_spinlock_t* spinlock));
29UV_UNUSED(static void uv_spinlock_lock(uv_spinlock_t* spinlock));
30UV_UNUSED(static void uv_spinlock_unlock(uv_spinlock_t* spinlock));
31UV_UNUSED(static int uv_spinlock_trylock(uv_spinlock_t* spinlock));
32
33UV_UNUSED(static void uv_spinlock_init(uv_spinlock_t* spinlock)) {
34 ACCESS_ONCE(int, spinlock->lock) = 0;
35}
36
37UV_UNUSED(static void uv_spinlock_lock(uv_spinlock_t* spinlock)) {
38 while (!uv_spinlock_trylock(spinlock)) cpu_relax();
39}
40
41UV_UNUSED(static void uv_spinlock_unlock(uv_spinlock_t* spinlock)) {
42 ACCESS_ONCE(int, spinlock->lock) = 0;
43}
44
45UV_UNUSED(static int uv_spinlock_trylock(uv_spinlock_t* spinlock)) {
46 /* TODO(bnoordhuis) Maybe change to a ticket lock to guarantee fair queueing.
47 * Not really critical until we have locks that are (frequently) contended
48 * for by several threads.
49 */
50 return 0 == cmpxchgi(&spinlock->lock, 0, 1);
51}
52
53#endif /* UV_SPINLOCK_H_ */
54