Method fcntlLock

Core/InterProcessLock_Android.cpp:50–92

}

bool FileLock::fcntlLock(LockType lockType, bool wait, bool unLockFirstIfNeeded, bool *tryAgain) {
    m_lockInfo.l_type = LockType2FlockType(lockType);
    auto FcntlLockOp = m_isAshmem ? F_SETLK : F_OFD_SETLK;
    auto FcntlLockOpW = m_isAshmem ? F_SETLKW : F_OFD_SETLKW;
    if (unLockFirstIfNeeded) {
        // try lock
        auto ret = fcntl(m_fd, FcntlLockOp, &m_lockInfo);
        if (ret == 0) {
            return true;
        }
        // lets be gentleman: unlock my shared-lock to prevent deadlock
        auto type = m_lockInfo.l_type;
        m_lockInfo.l_type = F_UNLCK;
        ret = fcntl(m_fd, FcntlLockOp, &m_lockInfo);
        if (ret != 0) {
            MMKVError("fail to try unlock first fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
        }
        m_lockInfo.l_type = type;
    }

    int cmd = wait ? FcntlLockOpW : FcntlLockOp;
    auto ret = fcntl(m_fd, cmd, &m_lockInfo);
    if (ret != 0) {
        if (tryAgain) {
            *tryAgain = (errno == EAGAIN);
        }
        if (wait) {
            MMKVError("fail to lock fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
        }
        // try recover my shared-lock
        if (unLockFirstIfNeeded) {
            m_lockInfo.l_type = LockType2FlockType(SharedLockType);
            ret = fcntl(m_fd, cmd, &m_lockInfo);
            if (ret != 0) {
                // let's hope this never happen
                MMKVError("fail to recover shared-lock fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
            }
        }
        return false;
    } else {
        return true;
    }
}

bool FileLock::fcntlUnLock(bool unlockToSharedLock) {
    m_lockInfo.l_type = static_cast<short>(unlockToSharedLock ? F_RDLCK : F_UNLCK);