/**
     * Locks this item.
     * @param level Whether lock is share or exclusive.
     * @param isDeep Whether lock is deep.
     * @param requestedTimeOut Lock timeout which was requested by client.
     * Server may ignore this parameter and set any timeout.
     * @param owner Owner of the lock as specified by client.
     * @returns
     * Instance of @see LockResult  with information about the lock.
     */
    public async lock(
        level: LockLevel | null,
        isDeep: boolean | null,
        requestedTimeOut: number | null,
        owner: string | null
    ): Promise<LockResult> {
        await this.requireUnlocked(level === LockLevel.shared);
        const token = randomBytes(16).toString('hex');
        //  If timeout is absent or infinit timeout requested,
        //  grant 5 minute lock.
        let timeOut = 5 * 60 * 1000;
        if (requestedTimeOut && (requestedTimeOut < 8640000000000000)) {
            timeOut = requestedTimeOut;
        }

        const lockInfo = new DateLockInfo();
        lockInfo.expiration = Date.now() + timeOut;
        lockInfo.isDeep = false;
        lockInfo.level = level !== null ? level : LockLevel.shared;
        lockInfo.lockRoot = this.path;
        lockInfo.lockToken = token;
        lockInfo.clientOwner = owner || '';
        lockInfo.timeOut = timeOut;

        this.saveLock(lockInfo);

        return new LockResult(lockInfo.lockToken, lockInfo.timeOut);
    }