| /* |
| * Copyright 2010-2015 Samy Al Bahra. |
| * 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. |
| */ |
| |
| #ifndef CK_SPINLOCK_DEC_H |
| #define CK_SPINLOCK_DEC_H |
| |
| #include <ck_backoff.h> |
| #include <ck_cc.h> |
| #include <ck_elide.h> |
| #include <ck_pr.h> |
| #include <ck_stdbool.h> |
| |
| #ifndef CK_F_SPINLOCK_DEC |
| #define CK_F_SPINLOCK_DEC |
| /* |
| * This is similar to the CACAS lock but makes use of an atomic decrement |
| * operation to check if the lock value was decremented to 0 from 1. The |
| * idea is that a decrement operation is cheaper than a compare-and-swap. |
| */ |
| struct ck_spinlock_dec { |
| unsigned int value; |
| }; |
| typedef struct ck_spinlock_dec ck_spinlock_dec_t; |
| |
| #define CK_SPINLOCK_DEC_INITIALIZER {1} |
| |
| CK_CC_INLINE static void |
| ck_spinlock_dec_init(struct ck_spinlock_dec *lock) |
| { |
| |
| lock->value = 1; |
| ck_pr_barrier(); |
| return; |
| } |
| |
| CK_CC_INLINE static bool |
| ck_spinlock_dec_trylock(struct ck_spinlock_dec *lock) |
| { |
| unsigned int value; |
| |
| value = ck_pr_fas_uint(&lock->value, 0); |
| ck_pr_fence_lock(); |
| return value == 1; |
| } |
| |
| CK_CC_INLINE static bool |
| ck_spinlock_dec_locked(struct ck_spinlock_dec *lock) |
| { |
| bool r; |
| |
| r = ck_pr_load_uint(&lock->value) != 1; |
| ck_pr_fence_acquire(); |
| return r; |
| } |
| |
| CK_CC_INLINE static void |
| ck_spinlock_dec_lock(struct ck_spinlock_dec *lock) |
| { |
| bool r; |
| |
| for (;;) { |
| /* |
| * Only one thread is guaranteed to decrement lock to 0. |
| * Overflow must be protected against. No more than |
| * UINT_MAX lock requests can happen while the lock is held. |
| */ |
| ck_pr_dec_uint_zero(&lock->value, &r); |
| if (r == true) |
| break; |
| |
| /* Load value without generating write cycles. */ |
| while (ck_pr_load_uint(&lock->value) != 1) |
| ck_pr_stall(); |
| } |
| |
| ck_pr_fence_lock(); |
| return; |
| } |
| |
| CK_CC_INLINE static void |
| ck_spinlock_dec_lock_eb(struct ck_spinlock_dec *lock) |
| { |
| ck_backoff_t backoff = CK_BACKOFF_INITIALIZER; |
| bool r; |
| |
| for (;;) { |
| ck_pr_dec_uint_zero(&lock->value, &r); |
| if (r == true) |
| break; |
| |
| while (ck_pr_load_uint(&lock->value) != 1) |
| ck_backoff_eb(&backoff); |
| } |
| |
| ck_pr_fence_lock(); |
| return; |
| } |
| |
| CK_CC_INLINE static void |
| ck_spinlock_dec_unlock(struct ck_spinlock_dec *lock) |
| { |
| |
| ck_pr_fence_unlock(); |
| |
| /* |
| * Unconditionally set lock value to 1 so someone can decrement lock |
| * to 0. |
| */ |
| ck_pr_store_uint(&lock->value, 1); |
| return; |
| } |
| |
| CK_ELIDE_PROTOTYPE(ck_spinlock_dec, ck_spinlock_dec_t, |
| ck_spinlock_dec_locked, ck_spinlock_dec_lock, |
| ck_spinlock_dec_locked, ck_spinlock_dec_unlock) |
| |
| CK_ELIDE_TRYLOCK_PROTOTYPE(ck_spinlock_dec, ck_spinlock_dec_t, |
| ck_spinlock_dec_locked, ck_spinlock_dec_trylock) |
| |
| #endif /* CK_F_SPINLOCK_DEC */ |
| #endif /* CK_SPINLOCK_DEC_H */ |