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
24 typedef struct {
25 int lock;
26 } uv_spinlock_t;
27
28 UV_UNUSED(static void uv_spinlock_init(uv_spinlock_t* spinlock));
29 UV_UNUSED(static void uv_spinlock_lock(uv_spinlock_t* spinlock));
30 UV_UNUSED(static void uv_spinlock_unlock(uv_spinlock_t* spinlock));
31 UV_UNUSED(static int uv_spinlock_trylock(uv_spinlock_t* spinlock));
32
UV_UNUSED(static void uv_spinlock_init (uv_spinlock_t * spinlock))33 UV_UNUSED(static void uv_spinlock_init(uv_spinlock_t* spinlock)) {
34 ACCESS_ONCE(int, spinlock->lock) = 0;
35 }
36
UV_UNUSED(static void uv_spinlock_lock (uv_spinlock_t * spinlock))37 UV_UNUSED(static void uv_spinlock_lock(uv_spinlock_t* spinlock)) {
38 while (!uv_spinlock_trylock(spinlock)) cpu_relax();
39 }
40
UV_UNUSED(static void uv_spinlock_unlock (uv_spinlock_t * spinlock))41 UV_UNUSED(static void uv_spinlock_unlock(uv_spinlock_t* spinlock)) {
42 ACCESS_ONCE(int, spinlock->lock) = 0;
43 }
44
UV_UNUSED(static int uv_spinlock_trylock (uv_spinlock_t * spinlock))45 UV_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