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// spin_lock.cpp
/**
* Copyright (C) 2010 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/>.
*/
#include "pch.h"
#include <time.h>
#include "spin_lock.h"
namespace mongo {
SpinLock::~SpinLock() {
#if defined(_WIN32)
DeleteCriticalSection(&_cs);
#endif
}
SpinLock::SpinLock()
#if defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
: _locked( false ) { }
#elif defined(_WIN32)
{ InitializeCriticalSectionAndSpinCount(&_cs, 4000); }
#else
: _mutex( "SpinLock" ) { }
#endif
void SpinLock::lock() {
#if defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
// fast path
if (!_locked && !__sync_lock_test_and_set(&_locked, true)) {
return;
}
// wait for lock
int wait = 1000;
while ((wait-- > 0) && (_locked)) {}
// if failed to grab lock, sleep
struct timespec t;
t.tv_sec = 0;
t.tv_nsec = 5000000;
while (__sync_lock_test_and_set(&_locked, true)) {
nanosleep(&t, NULL);
}
#elif defined(_WIN32)
EnterCriticalSection(&_cs);
#else
// WARNING Missing spin lock in this platform. This can potentially
// be slow.
_mutex.lock();
#endif
}
void SpinLock::unlock() {
#if defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
__sync_lock_release(&_locked);
#elif defined(WIN32)
LeaveCriticalSection(&_cs);
#else
_mutex.unlock();
#endif
}
} // namespace mongo
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