text: /*
   * Copyright 2010-2014 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 <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;
  
  	ck_pr_fence_load();
  	position = ck_pr_load_uint(&lock->next) & lock->mask;
  	ck_pr_fence_load();
  
  	return ck_pr_load_uint(&lock->slots[position].locked);
  }
  
  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_acquire();
  
  	*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_release();
  
  	/* 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 */
  
  