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// spin_lock.h
/**
* Copyright (C) 2008 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#pragma once
#include "mutex.h"
namespace mongo {
/**
* The spinlock currently requires late GCC support routines to be efficient.
* Other platforms default to a mutex implemenation.
*/
class SpinLock : boost::noncopyable {
public:
SpinLock();
~SpinLock();
static bool isfast(); // true if a real spinlock on this platform
private:
#if defined(_WIN32)
CRITICAL_SECTION _cs;
public:
void lock() {EnterCriticalSection(&_cs); }
void unlock() { LeaveCriticalSection(&_cs); }
#elif defined(__USE_XOPEN2K)
pthread_spinlock_t _lock;
void _lk();
public:
void unlock() { pthread_spin_unlock(&_lock); }
void lock() {
if ( pthread_spin_trylock( &_lock ) == 0 )
return;
_lk();
}
#elif defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
volatile bool _locked;
public:
void unlock() {__sync_lock_release(&_locked); }
void lock();
#else
// default to a mutex if not implemented
SimpleMutex _mutex;
public:
void unlock() { _mutex.unlock(); }
void lock() { _mutex.lock(); }
#endif
};
class scoped_spinlock : boost::noncopyable {
public:
scoped_spinlock( SpinLock& l ) : _l(l) {
_l.lock();
}
~scoped_spinlock() {
_l.unlock();}
private:
SpinLock& _l;
};
} // namespace mongo
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