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 33 UV_UNUSED(static void uv_spinlock_init(uv_spinlock_t* spinlock)) { 34 ACCESS_ONCE(int, spinlock->lock) = 0; 35 } 36 37 UV_UNUSED(static void uv_spinlock_lock(uv_spinlock_t* spinlock)) { 38 while (!uv_spinlock_trylock(spinlock)) cpu_relax(); 39 } 40 41 UV_UNUSED(static void uv_spinlock_unlock(uv_spinlock_t* spinlock)) { 42 ACCESS_ONCE(int, spinlock->lock) = 0; 43 } 44 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