libcilkrts/runtime/worker_mutex.c

/* worker_mutex.c                  -*-C-*-
 *
 *************************************************************************
 *
 *  Copyright (C) 2009-2016, Intel Corporation
 *  All rights reserved.
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 *      from this software without specific prior written permission.
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 *  PLEASE NOTE: This file is a downstream copy of a file mainitained in
 *  a repository at cilkplus.org. Changes made to this file that are not
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 **************************************************************************/

#include "worker_mutex.h"
#include "bug.h"
#include "os.h"
#include "stats.h"

/* m->lock == 1 means that mutex M is locked */
#define TRY_ACQUIRE(m) (__cilkrts_xchg(&(m)->lock, 1) == 0)

/* ICC 11.1+ understands release semantics and generates an
   ordinary store with a software memory barrier. */
#if __ICC >= 1110
#define RELEASE(m) __sync_lock_release(&(m)->lock)
#else
#define RELEASE(m) __cilkrts_xchg(&(m)->lock, 0)
#endif

void __cilkrts_mutex_init(struct mutex *m)
{
    m->owner = 0;

    // Use a simple assignment so Inspector doesn't bug us about the
    // interlocked exchange doing a read of an uninitialized variable.
    // By definition there can't be a race when we're initializing the
    // lock...
    m->lock = 0;
}

void __cilkrts_mutex_lock(__cilkrts_worker *w, struct mutex *m)
{
    int count;
    const int maxspin = 1000; /* SWAG */

    NOTE_INTERVAL(w, INTERVAL_MUTEX_LOCK);
    if (!TRY_ACQUIRE(m)) {
        START_INTERVAL(w, INTERVAL_MUTEX_LOCK_SPINNING);
        count = 0;
        do {
            do {
                __cilkrts_short_pause();
                if (++count >= maxspin) {
                    STOP_INTERVAL(w, INTERVAL_MUTEX_LOCK_SPINNING);
                    START_INTERVAL(w, INTERVAL_MUTEX_LOCK_YIELDING);
                    /* let the OS reschedule every once in a while */
                    __cilkrts_yield();
                    STOP_INTERVAL(w, INTERVAL_MUTEX_LOCK_YIELDING);
                    START_INTERVAL(w, INTERVAL_MUTEX_LOCK_SPINNING);
                    count = 0;
                }
            } while (m->lock != 0);
        } while (!TRY_ACQUIRE(m));
        STOP_INTERVAL(w, INTERVAL_MUTEX_LOCK_SPINNING);
    }

    CILK_ASSERT(m->owner == 0);
    m->owner = w;
}

int __cilkrts_mutex_trylock(__cilkrts_worker *w, struct mutex *m)
{
    NOTE_INTERVAL(w, INTERVAL_MUTEX_TRYLOCK);
    if (TRY_ACQUIRE(m)) {
        CILK_ASSERT(m->owner == 0);
        m->owner = w;
        return 1;
    } else {
        return 0;
    }
}

void __cilkrts_mutex_unlock(__cilkrts_worker *w, struct mutex *m)
{
    CILK_ASSERT(m->owner == w);
    m->owner = 0;
    RELEASE(m);
}

void __cilkrts_mutex_destroy(__cilkrts_worker *w, struct mutex *m)
{
    (void)w; /* unused */
    (void)m; /* unused */
}

/* End worker_mutex.c */