FreeBSD/Linux Kernel Cross Reference
sys/contrib/ck/src/ck_barrier_dissemination.c

     /*
      * Copyright 2011-2015 Samy Al Bahra.
      * Copyright 2011 David Joseph.
      * 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.
     */
    
    #include <ck_barrier.h>
    #include <ck_cc.h>
    #include <ck_pr.h>
    #include <ck_spinlock.h>
    
    #include "ck_internal.h"
    
    void
    ck_barrier_dissemination_init(struct ck_barrier_dissemination *barrier,
        struct ck_barrier_dissemination_flag **barrier_internal,
        unsigned int nthr)
    {
            unsigned int i, j, k, size, offset;
            bool p = nthr & (nthr - 1);
    
            barrier->nthr = nthr;
            barrier->size = size = ck_internal_log(ck_internal_power_2(nthr));
            ck_pr_store_uint(&barrier->tid, 0);
    
            for (i = 0; i < nthr; ++i) {
                    barrier[i].flags[0] = barrier_internal[i];
                    barrier[i].flags[1] = barrier_internal[i] + size;
            }
    
            for (i = 0; i < nthr; ++i) {
                    for (k = 0, offset = 1; k < size; ++k, offset <<= 1) {
                            /*
                             * Determine the thread's partner, j, for the current round, k.
                             * Partners are chosen such that by the completion of the barrier,
                             * every thread has been directly (having one of its flag set) or
                             * indirectly (having one of its partners's flags set) signaled
                             * by every other thread in the barrier.
                             */
                            if (p == false)
                                    j = (i + offset) & (nthr - 1);
                            else
                                    j = (i + offset) % nthr;
    
                            /* Set the thread's partner for round k. */
                            barrier[i].flags[0][k].pflag = &barrier[j].flags[0][k].tflag;
                            barrier[i].flags[1][k].pflag = &barrier[j].flags[1][k].tflag;
    
                            /* Set the thread's flags to false. */
                            barrier[i].flags[0][k].tflag = barrier[i].flags[1][k].tflag = 0;
                    }
            }
    
            return;
    }
    
    void
    ck_barrier_dissemination_subscribe(struct ck_barrier_dissemination *barrier,
        struct ck_barrier_dissemination_state *state)
    {
    
            state->parity = 0;
            state->sense = ~0;
            state->tid = ck_pr_faa_uint(&barrier->tid, 1);
            return;
    }
    
    unsigned int
    ck_barrier_dissemination_size(unsigned int nthr)
    {
    
            return (ck_internal_log(ck_internal_power_2(nthr)) << 1);
    }
    
    void
    ck_barrier_dissemination(struct ck_barrier_dissemination *barrier,
        struct ck_barrier_dissemination_state *state)
    {
           unsigned int i;
           unsigned int size = barrier->size;
   
           for (i = 0; i < size; ++i) {
                   unsigned int *pflag, *tflag;
   
                   pflag = barrier[state->tid].flags[state->parity][i].pflag;
                   tflag = &barrier[state->tid].flags[state->parity][i].tflag;
   
                   /* Unblock current partner. */
                   ck_pr_store_uint(pflag, state->sense);
   
                   /* Wait until some other thread unblocks this one. */
                   while (ck_pr_load_uint(tflag) != state->sense)
                           ck_pr_stall();
           }
   
           /*
            * Dissemination barriers use two sets of flags to prevent race conditions
            * between successive calls to the barrier. Parity indicates which set will
            * be used for the next barrier. They also use a sense reversal technique
            * to avoid re-initialization of the flags for every two calls to the barrier.
            */
           if (state->parity == 1)
                   state->sense = ~state->sense;
   
           state->parity = 1 - state->parity;
   
           ck_pr_fence_acquire();
           return;
   }

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