Method try_lock

src/bvar/utils/lock_timer.h:255–263

    }

    bool try_lock() { 
        _timer.start();
        const bool rc = _lock.try_lock(); 
        _timer.stop();
        if (!rc) {
            _mutex->recorder() << _timer.u_elapsed();
        }
        return rc;
    }

    void unlock() { 
        _lock.unlock();