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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"
#else
#include <atomic>
#endif
#include "mongo/base/disallow_copying.h"
#include "mongo/platform/compiler.h"
#include "mongo/stdx/mutex.h"
namespace mongo {
#if defined(_WIN32)
class SpinLock {
MONGO_DISALLOW_COPYING(SpinLock);
public:
SpinLock() {
InitializeCriticalSectionAndSpinCount(&_cs, 4000);
}
~SpinLock() {
DeleteCriticalSection(&_cs);
}
void lock() {
EnterCriticalSection(&_cs);
}
void unlock() {
LeaveCriticalSection(&_cs);
}
private:
CRITICAL_SECTION _cs;
};
#else
class SpinLock {
MONGO_DISALLOW_COPYING(SpinLock);
public:
SpinLock() = default;
void unlock() {
_locked.clear(std::memory_order_release);
}
void lock() {
if (MONGO_likely(_tryLock()))
return;
_lockSlowPath();
}
private:
bool _tryLock() {
bool wasLocked = _locked.test_and_set(std::memory_order_acquire);
return !wasLocked;
}
void _lockSlowPath();
// Initializes to the cleared state.
std::atomic_flag _locked = ATOMIC_FLAG_INIT; // NOLINT
};
#endif
using scoped_spinlock = stdx::lock_guard<SpinLock>;
} // namespace mongo
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