| /* |
| * 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 */ |