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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/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#pragma once
#ifdef _WIN32
#include "mongo/platform/windows_basic.h"
#endif
#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 ( MONGO_likely( 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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