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

     /*
      * Copyright 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_TFLOCK_TICKET_H
    #define CK_TFLOCK_TICKET_H
    
    /*
     * This is an implementation of task-fair locks derived from the work
     * described in:
     *      John M. Mellor-Crummey and Michael L. Scott. 1991.
     *      Scalable reader-writer synchronization for shared-memory
     *      multiprocessors. SIGPLAN Not. 26, 7 (April 1991), 106-113.
     */
    
    #include <ck_cc.h>
    #include <ck_pr.h>
    
    struct ck_tflock_ticket {
            uint32_t request;
            uint32_t completion;
    };
    typedef struct ck_tflock_ticket ck_tflock_ticket_t;
    
    #define CK_TFLOCK_TICKET_INITIALIZER { 0, 0 }
    
    #define CK_TFLOCK_TICKET_RC_INCR        0x10000U        /* Read-side increment. */
    #define CK_TFLOCK_TICKET_WC_INCR        0x1U            /* Write-side increment. */
    #define CK_TFLOCK_TICKET_W_MASK         0xffffU         /* Write-side mask. */
    #define CK_TFLOCK_TICKET_WC_TOPMSK      0x8000U         /* Write clear mask for overflow. */
    #define CK_TFLOCK_TICKET_RC_TOPMSK      0x80000000U     /* Read clear mask for overflow. */
    
    CK_CC_INLINE static uint32_t
    ck_tflock_ticket_fca_32(uint32_t *target, uint32_t mask, uint32_t delta)
    {
            uint32_t snapshot = ck_pr_load_32(target);
            uint32_t goal;
    
            for (;;) {
                    goal = (snapshot & ~mask) + delta;
                    if (ck_pr_cas_32_value(target, snapshot, goal, &snapshot) == true)
                            break;
    
                    ck_pr_stall();
            }
    
            return snapshot;
    }
    
    CK_CC_INLINE static void
    ck_tflock_ticket_init(struct ck_tflock_ticket *pf)
    {
    
            pf->request = pf->completion = 0;
            ck_pr_barrier();
            return;
    }
    
    CK_CC_INLINE static void
    ck_tflock_ticket_write_lock(struct ck_tflock_ticket *lock)
    {
            uint32_t previous;
    
            previous = ck_tflock_ticket_fca_32(&lock->request, CK_TFLOCK_TICKET_WC_TOPMSK,
                CK_TFLOCK_TICKET_WC_INCR);
            ck_pr_fence_atomic_load();
            while (ck_pr_load_32(&lock->completion) != previous)
                    ck_pr_stall();
    
            ck_pr_fence_lock();
            return;
    }
    
    CK_CC_INLINE static void
    ck_tflock_ticket_write_unlock(struct ck_tflock_ticket *lock)
    {
    
           ck_pr_fence_unlock();
           ck_tflock_ticket_fca_32(&lock->completion, CK_TFLOCK_TICKET_WC_TOPMSK,
               CK_TFLOCK_TICKET_WC_INCR);
           return;
   }
   
   CK_CC_INLINE static void
   ck_tflock_ticket_read_lock(struct ck_tflock_ticket *lock)
   {
           uint32_t previous;
   
           previous = ck_tflock_ticket_fca_32(&lock->request,
               CK_TFLOCK_TICKET_RC_TOPMSK, CK_TFLOCK_TICKET_RC_INCR) &
               CK_TFLOCK_TICKET_W_MASK;
   
           ck_pr_fence_atomic_load();
   
           while ((ck_pr_load_32(&lock->completion) &
               CK_TFLOCK_TICKET_W_MASK) != previous) {
                   ck_pr_stall();
           }
   
           ck_pr_fence_lock();
           return;
   }
   
   CK_CC_INLINE static void
   ck_tflock_ticket_read_unlock(struct ck_tflock_ticket *lock)
   {
   
           ck_pr_fence_unlock();
           ck_tflock_ticket_fca_32(&lock->completion, CK_TFLOCK_TICKET_RC_TOPMSK,
               CK_TFLOCK_TICKET_RC_INCR);
           return;
   }
   
   #endif /* CK_TFLOCK_TICKET_H */

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