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Diffstat (limited to 'include/spinlock/anderson.h')
| -rw-r--r-- | include/spinlock/anderson.h | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/include/spinlock/anderson.h b/include/spinlock/anderson.h new file mode 100644 index 0000000..bebc5d8 --- /dev/null +++ b/include/spinlock/anderson.h @@ -0,0 +1,167 @@ +/* + * 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_ANDERSON_H +#define CK_SPINLOCK_ANDERSON_H + +#include <ck_cc.h> +#include <ck_limits.h> +#include <ck_md.h> +#include <ck_pr.h> +#include <ck_stdbool.h> + +#ifndef CK_F_SPINLOCK_ANDERSON +#define CK_F_SPINLOCK_ANDERSON +/* + * This is an implementation of Anderson's array-based queuing lock. + */ +struct ck_spinlock_anderson_thread { + unsigned int locked; + unsigned int position; +}; +typedef struct ck_spinlock_anderson_thread ck_spinlock_anderson_thread_t; + +struct ck_spinlock_anderson { + struct ck_spinlock_anderson_thread *slots; + unsigned int count; + unsigned int wrap; + unsigned int mask; + char pad[CK_MD_CACHELINE - sizeof(unsigned int) * 3 - sizeof(void *)]; + unsigned int next; +}; +typedef struct ck_spinlock_anderson ck_spinlock_anderson_t; + +CK_CC_INLINE static void +ck_spinlock_anderson_init(struct ck_spinlock_anderson *lock, + struct ck_spinlock_anderson_thread *slots, + unsigned int count) +{ + unsigned int i; + + slots[0].locked = false; + slots[0].position = 0; + for (i = 1; i < count; i++) { + slots[i].locked = true; + slots[i].position = i; + } + + lock->slots = slots; + lock->count = count; + lock->mask = count - 1; + lock->next = 0; + + /* + * If the number of threads is not a power of two then compute + * appropriate wrap-around value in the case of next slot counter + * overflow. + */ + if (count & (count - 1)) + lock->wrap = (UINT_MAX % count) + 1; + else + lock->wrap = 0; + + ck_pr_barrier(); + return; +} + +CK_CC_INLINE static bool +ck_spinlock_anderson_locked(struct ck_spinlock_anderson *lock) +{ + unsigned int position; + bool r; + + position = ck_pr_load_uint(&lock->next) & lock->mask; + r = ck_pr_load_uint(&lock->slots[position].locked); + ck_pr_fence_acquire(); + return r; +} + +CK_CC_INLINE static void +ck_spinlock_anderson_lock(struct ck_spinlock_anderson *lock, + struct ck_spinlock_anderson_thread **slot) +{ + unsigned int position, next; + unsigned int count = lock->count; + + /* + * If count is not a power of 2, then it is possible for an overflow + * to reallocate beginning slots to more than one thread. To avoid this + * use a compare-and-swap. + */ + if (lock->wrap != 0) { + position = ck_pr_load_uint(&lock->next); + + do { + if (position == UINT_MAX) + next = lock->wrap; + else + next = position + 1; + } while (ck_pr_cas_uint_value(&lock->next, position, + next, &position) == false); + + position %= count; + } else { + position = ck_pr_faa_uint(&lock->next, 1); + position &= lock->mask; + } + + /* Serialize with respect to previous thread's store. */ + ck_pr_fence_load(); + + /* + * Spin until slot is marked as unlocked. First slot is initialized to + * false. + */ + while (ck_pr_load_uint(&lock->slots[position].locked) == true) + ck_pr_stall(); + + /* Prepare slot for potential re-use by another thread. */ + ck_pr_store_uint(&lock->slots[position].locked, true); + ck_pr_fence_lock(); + + *slot = lock->slots + position; + return; +} + +CK_CC_INLINE static void +ck_spinlock_anderson_unlock(struct ck_spinlock_anderson *lock, + struct ck_spinlock_anderson_thread *slot) +{ + unsigned int position; + + ck_pr_fence_unlock(); + + /* Mark next slot as available. */ + if (lock->wrap == 0) + position = (slot->position + 1) & lock->mask; + else + position = (slot->position + 1) % lock->count; + + ck_pr_store_uint(&lock->slots[position].locked, false); + return; +} +#endif /* CK_F_SPINLOCK_ANDERSON */ +#endif /* CK_SPINLOCK_ANDERSON_H */ |