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SpinLock.h
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SpinLock.h
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/*
Pharmer: Efficient and Exact 3D Pharmacophore Search
Copyright (C) 2011 David Ryan Koes and the University of Pittsburgh
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
/*
* SpinLock.h
*
* Created on: Feb 10, 2010
* Author: dkoes
*
* A very simple spinlock. Separtes lock var (mutex) from locker so destructor can release lock.
*/
#ifndef SPINLOCK_H_
#define SPINLOCK_H_
#include <cassert>
enum SpinMutexEnum {SpinMutexUnlocked, SpinMutexLocked};
//make class for automatic initialization
struct SpinMutex
{
struct {
long prevent_false_sharing[7];
volatile SpinMutexEnum val;
long prevent_false_sharing_after[8];
};
SpinMutex(): val(SpinMutexUnlocked) {}
SpinMutex(SpinMutexEnum v): val(v) {}
};
class SpinLock
{
SpinMutex& mutex;
bool holdsLock; //true if this lock has the mutex
public:
static void acquire(SpinMutex& m)
{
while(!__sync_bool_compare_and_swap (&m.val, SpinMutexUnlocked, SpinMutexLocked))
; //spin if was already locked
assert(m.val == SpinMutexLocked);
}
static void release(SpinMutex& m)
{
assert(m.val == SpinMutexLocked);
m.val = SpinMutexUnlocked;
}
void acquire() { acquire(mutex); holdsLock = true; }
void release() { if(holdsLock) release(mutex); holdsLock = false;}
//acquire mutex
SpinLock(SpinMutex& m, bool lock=true): mutex(m)
{
if(lock)
acquire();
holdsLock = lock;
}
virtual ~SpinLock()
{
//always release if we're holding the lock
if(holdsLock)
release();
}
};
#endif /* SPINLOCK_H_ */