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85 lines
2.0 KiB
C++
85 lines
2.0 KiB
C++
// spin_lock.cpp
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/**
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* Copyright (C) 2010 10gen Inc.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License, version 3,
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "pch.h"
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#include <time.h>
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#include "spin_lock.h"
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namespace mongo {
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SpinLock::~SpinLock() {
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#if defined(_WIN32)
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DeleteCriticalSection(&_cs);
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#endif
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}
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SpinLock::SpinLock()
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#if defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
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: _locked( false ) { }
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#elif defined(_WIN32)
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{ InitializeCriticalSectionAndSpinCount(&_cs, 4000); }
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#else
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: _mutex( "SpinLock" ) { }
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#endif
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void SpinLock::lock(){
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#if defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
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// fast path
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if (!_locked && !__sync_lock_test_and_set(&_locked, true)) {
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return;
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}
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// wait for lock
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int wait = 1000;
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while ((wait-- > 0) && (_locked)) {}
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// if failed to grab lock, sleep
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struct timespec t;
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t.tv_sec = 0;
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t.tv_nsec = 5000000;
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while (__sync_lock_test_and_set(&_locked, true)) {
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nanosleep(&t, NULL);
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}
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#elif defined(_WIN32)
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EnterCriticalSection(&_cs);
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#else
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// WARNING Missing spin lock in this platform. This can potentially
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// be slow.
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_mutex.lock();
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#endif
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}
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void SpinLock::unlock(){
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#if defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
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__sync_lock_release(&_locked);
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#elif defined(WIN32)
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LeaveCriticalSection(&_cs);
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#else
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_mutex.unlock();
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#endif
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}
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} // namespace mongo
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