mirror of
https://github.com/Tencent/MMKV.git
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guoling
104 lines
3.2 KiB
C++
104 lines
3.2 KiB
C++
/*
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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_ANDROID
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# include "MMKVLog.h"
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# include <sys/file.h>
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# include <unistd.h>
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namespace mmkv {
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FileLock::FileLock(MMKVFileHandle_t fd, bool isAshmem)
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: m_fd(fd), m_sharedLockCount(0), m_exclusiveLockCount(0), m_isAshmem(isAshmem) {
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m_lockInfo.l_type = F_WRLCK;
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m_lockInfo.l_start = 0;
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m_lockInfo.l_whence = SEEK_SET;
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m_lockInfo.l_len = 0;
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m_lockInfo.l_pid = 0;
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}
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static short LockType2FlockType(LockType lockType) {
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switch (lockType) {
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case SharedLockType:
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return F_RDLCK;
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case ExclusiveLockType:
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return F_WRLCK;
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}
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}
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bool FileLock::ashmemLock(LockType lockType, bool wait, bool unLockFirstIfNeeded, bool *tryAgain) {
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m_lockInfo.l_type = LockType2FlockType(lockType);
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if (unLockFirstIfNeeded) {
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// try lock
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auto ret = fcntl(m_fd, F_SETLK, &m_lockInfo);
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if (ret == 0) {
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return true;
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}
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// lets be gentleman: unlock my shared-lock to prevent deadlock
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auto type = m_lockInfo.l_type;
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m_lockInfo.l_type = F_UNLCK;
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ret = fcntl(m_fd, F_SETLK, &m_lockInfo);
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if (ret != 0) {
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MMKVError("fail to try unlock first fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
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}
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m_lockInfo.l_type = type;
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}
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int cmd = wait ? F_SETLKW : F_SETLK;
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auto ret = fcntl(m_fd, cmd, &m_lockInfo);
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if (ret != 0) {
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if (tryAgain) {
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*tryAgain = (errno == EAGAIN);
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}
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if (wait) {
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MMKVError("fail to lock fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
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}
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// try recover my shared-lock
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if (unLockFirstIfNeeded) {
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m_lockInfo.l_type = LockType2FlockType(SharedLockType);
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ret = fcntl(m_fd, cmd, &m_lockInfo);
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if (ret != 0) {
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// let's hope this never happen
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MMKVError("fail to recover shared-lock fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
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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::ashmemUnLock(bool unlockToSharedLock) {
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m_lockInfo.l_type = static_cast<short>(unlockToSharedLock ? F_RDLCK : F_UNLCK);
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auto ret = fcntl(m_fd, F_SETLK, &m_lockInfo);
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if (ret != 0) {
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MMKVError("fail to unlock fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
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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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} // namespace mmkv
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#endif // MMKV_ANDROID
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