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Diffstat (limited to 'include/spinlock/dec.h')
| -rw-r--r-- | include/spinlock/dec.h | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/include/spinlock/dec.h b/include/spinlock/dec.h new file mode 100644 index 0000000..11d36dd --- /dev/null +++ b/include/spinlock/dec.h @@ -0,0 +1,143 @@ +/* + * 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; + + 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 */ |