gcc/libcilkrts/runtime/spin_mutex.c

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/* spin_mutex.c -*-C-*-
*
*************************************************************************
*
* @copyright
* Copyright (C) 2009-2013, Intel Corporation
* All rights reserved.
*
* @copyright
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * 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.
* * Neither the name of Intel Corporation nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* @copyright
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT
* HOLDER 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 "spin_mutex.h"
#include "bug.h"
#include "os.h"
#include "stats.h"
// TBD (11/30/12): We should be doing a conditional test-xchg instead
// of an unconditional xchg operation for the spin mutex.
/* 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
spin_mutex* spin_mutex_create()
{
spin_mutex* mutex = (spin_mutex*)__cilkrts_malloc(sizeof(spin_mutex));
spin_mutex_init(mutex);
return mutex;
}
void spin_mutex_init(struct spin_mutex *m)
{
// 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 spin_mutex_lock(struct spin_mutex *m)
{
int count;
const int maxspin = 1000; /* SWAG */
if (!TRY_ACQUIRE(m)) {
count = 0;
do {
do {
__cilkrts_short_pause();
if (++count >= maxspin) {
/* let the OS reschedule every once in a while */
__cilkrts_yield();
count = 0;
}
} while (m->lock != 0);
} while (!TRY_ACQUIRE(m));
}
}
int spin_mutex_trylock(struct spin_mutex *m)
{
return TRY_ACQUIRE(m);
}
void spin_mutex_unlock(struct spin_mutex *m)
{
RELEASE(m);
}
void spin_mutex_destroy(struct spin_mutex *m)
{
__cilkrts_free(m);
}
/* End spin_mutex.c */