FreeBSD/Linux Kernel Cross Reference
sys/contrib/ck/include/spinlock/clh.h

     /*
      * 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_CLH_H
    #define CK_SPINLOCK_CLH_H
    
    #include <ck_cc.h>
    #include <ck_limits.h>
    #include <ck_pr.h>
    #include <ck_stdbool.h>
    #include <ck_stddef.h>
    
    #ifndef CK_F_SPINLOCK_CLH
    #define CK_F_SPINLOCK_CLH
    
    struct ck_spinlock_clh {
            unsigned int wait;
            struct ck_spinlock_clh *previous;
    };
    typedef struct ck_spinlock_clh ck_spinlock_clh_t;
    
    CK_CC_INLINE static void
    ck_spinlock_clh_init(struct ck_spinlock_clh **lock, struct ck_spinlock_clh *unowned)
    {
    
            unowned->previous = NULL;
            unowned->wait = false;
            *lock = unowned;
            ck_pr_barrier();
            return;
    }
    
    CK_CC_INLINE static bool
    ck_spinlock_clh_locked(struct ck_spinlock_clh **queue)
    {
            struct ck_spinlock_clh *head;
            bool r;
    
            head = ck_pr_load_ptr(queue);
            r = ck_pr_load_uint(&head->wait);
            ck_pr_fence_acquire();
            return r;
    }
    
    CK_CC_INLINE static void
    ck_spinlock_clh_lock(struct ck_spinlock_clh **queue, struct ck_spinlock_clh *thread)
    {
            struct ck_spinlock_clh *previous;
    
            /* Indicate to the next thread on queue that they will have to block. */
            thread->wait = true;
            ck_pr_fence_store_atomic();
    
            /*
             * Mark current request as last request. Save reference to previous
             * request.
             */
            previous = ck_pr_fas_ptr(queue, thread);
            thread->previous = previous;
    
            /* Wait until previous thread is done with lock. */
            ck_pr_fence_load();
            while (ck_pr_load_uint(&previous->wait) == true)
                    ck_pr_stall();
    
            ck_pr_fence_lock();
            return;
    }
    
    CK_CC_INLINE static void
    ck_spinlock_clh_unlock(struct ck_spinlock_clh **thread)
    {
            struct ck_spinlock_clh *previous;
    
            /*
             * If there are waiters, they are spinning on the current node wait
            * flag. The flag is cleared so that the successor may complete an
            * acquisition. If the caller is pre-empted then the predecessor field
            * may be updated by a successor's lock operation. In order to avoid
            * this, save a copy of the predecessor before setting the flag.
            */
           previous = thread[0]->previous;
   
           /*
            * We have to pay this cost anyways, use it as a compiler barrier too.
            */
           ck_pr_fence_unlock();
           ck_pr_store_uint(&(*thread)->wait, false);
   
           /*
            * Predecessor is guaranteed not to be spinning on previous request,
            * so update caller to use previous structure. This allows successor
            * all the time in the world to successfully read updated wait flag.
            */
           *thread = previous;
           return;
   }
   #endif /* CK_F_SPINLOCK_CLH */
   #endif /* CK_SPINLOCK_CLH_H */

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