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https://github.com/Tencent/MMKV.git
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guoling
109 lines
3.5 KiB
C++
Executable File
109 lines
3.5 KiB
C++
Executable File
/*
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* Tencent is pleased to support the open source community by making
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* MMKV available.
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*
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* Copyright (C) 2019 THL A29 Limited, a Tencent company.
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* All rights reserved.
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*
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* Licensed under the BSD 3-Clause License (the "License"); you may not use
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* this file except in compliance with the License. You may obtain a copy of
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* the License at
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*
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* https://opensource.org/licenses/BSD-3-Clause
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "InterProcessLock.h"
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#ifdef MMKV_WIN32
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# include "MMKVLog.h"
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namespace mmkv {
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static DWORD LockType2Flag(LockType lockType) {
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DWORD flag = 0;
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switch (lockType) {
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case SharedLockType:
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flag = 0;
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break;
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case ExclusiveLockType:
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flag = LOCKFILE_EXCLUSIVE_LOCK;
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break;
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}
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return flag;
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}
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bool FileLock::platformLock(LockType lockType, bool wait, bool unLockFirstIfNeeded, bool *tryAgain) {
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auto realLockType = LockType2Flag(lockType);
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auto flag = wait ? realLockType : (realLockType | LOCKFILE_FAIL_IMMEDIATELY);
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if (unLockFirstIfNeeded) {
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/* try exclusive-lock above shared-lock will always fail in Win32
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auto ret = LockFileEx(m_fd, realLockType | LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, &m_overLapped);
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if (ret) {
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return true;
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}*/
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// let's be gentleman: unlock my shared-lock to prevent deadlock
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auto ret = UnlockFileEx(m_fd, 0, 1, 0, &m_overLapped);
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if (!ret) {
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auto lastError = GetLastError();
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if (lastError != ERROR_NOT_LOCKED) {
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MMKVError("fail to try unlock first fd=%p, error:%d", m_fd, lastError);
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}
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}
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}
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auto ret = LockFileEx(m_fd, flag, 0, 1, 0, &m_overLapped);
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if (!ret) {
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if (tryAgain) {
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*tryAgain = (GetLastError() == ERROR_LOCK_VIOLATION);
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}
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if (wait) {
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MMKVError("fail to lock fd=%p, error:%d", m_fd, GetLastError());
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}
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// try recover my shared-lock
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if (unLockFirstIfNeeded) {
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ret = LockFileEx(m_fd, LockType2Flag(SharedLockType), 0, 1, 0, &m_overLapped);
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if (!ret) {
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// let's hope this never happen
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MMKVError("fail to recover shared-lock fd=%p, error:%d", m_fd, GetLastError());
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}
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}
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return false;
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} else {
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return true;
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}
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}
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bool FileLock::platformUnLock(bool unlockToSharedLock) {
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/* quote from MSDN:
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* If the same range is locked with an exclusive and a shared lock,
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* two unlock operations are necessary to unlock the region;
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* the first unlock operation unlocks the exclusive lock,
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* the second unlock operation unlocks the shared lock.
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*/
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if (unlockToSharedLock) {
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auto flag = LockType2Flag(SharedLockType);
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if (!LockFileEx(m_fd, flag, 0, 1, 0, &m_overLapped)) {
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MMKVError("fail to roll back to shared-lock, error:%d", GetLastError());
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}
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}
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auto ret = UnlockFileEx(m_fd, 0, 1, 0, &m_overLapped);
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if (!ret) {
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auto lastError = GetLastError();
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if (lastError != ERROR_NOT_LOCKED) {
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MMKVError("fail to unlock fd=%p, error:%d", m_fd, lastError);
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return false;
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}
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}
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return true;
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}
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} // namespace mmkv
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#endif // MMKV_WIN32
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