Method try_acquire_for

tests/BS_thread_pool_test.cpp:204–215

     */
    template <class Rep, class Period>
    bool try_acquire_for(const std::chrono::duration<Rep, Period>& rel_time)
    {
        std::unique_lock lock(mutex);
        if (!cv.wait_for(lock, rel_time,
                [this]
                {
                    return counter > 0;
                }))
            return false;
        --counter;
        return true;
    }

    /**
     * @brief Tries to atomically decrement the internal counter by 1 if it is greater than 0; otherwise blocks until it is greater than 0 and can successfully decrement the internal counter, or the `abs_time` time point has been passed.