/* * 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 #include #include #include #include #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); if (value == 1) { ck_pr_fence_acquire(); return true; } return false; } CK_CC_INLINE static bool ck_spinlock_dec_locked(struct ck_spinlock_dec *lock) { ck_pr_fence_load(); return ck_pr_load_uint(&lock->value) != 1; } 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_acquire(); 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_acquire(); return; } CK_CC_INLINE static void ck_spinlock_dec_unlock(struct ck_spinlock_dec *lock) { ck_pr_fence_release(); /* 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 */