asio::read 超时 [英] asio::read with timeout

问题描述

我需要知道如何超时读取(同步或异步无关紧要).我想检查设备是否连接了串口.

I need to know how to read (sync or async doesn't matters) with a timeout. I want to check if a device is connected with a serial port or not.

为此，我使用 asio::write 然后等待设备的响应.

For that I use asio::write and then I wait for the response of the device.

如果连接了设备 asio::read(serial, boost::asio::buffer(&r,1)) 工作正常，但如果没有设备，程序会停止，这这就是为什么我需要超时

If a device is connected asio::read(serial, boost::asio::buffer(&r,1)) works fine but if there is no device the program stops, which is is why I need the timeout

我知道我需要一个 deadline_timer 但我不知道如何在 async_read 函数中使用它.

I know that I need a deadline_timer but I have no idea how to use it in the async_read function.

它是如何工作的一个例子会非常有帮助.

An example of how it works would be really helpful.

我知道有很多类似的主题，我阅读了很多，但我找不到可以帮助我解决问题的解决方案！

I know that there are many similar threads and I read lot of them but I can't find a solution that helps me solving my problem!

推荐答案

Igor R 发布的代码没有为我编译.这是我对他的代码的改进版本，效果很好.它使用 lambdas 来摆脱 set_result 辅助函数.

The code posted by Igor R. did not compile for me. Here is my improved version of his code, which works perfectly. It uses lambdas to get rid of the set_result helper function.

template <typename SyncReadStream, typename MutableBufferSequence>
void readWithTimeout(SyncReadStream& s, const MutableBufferSequence& buffers, const boost::asio::deadline_timer::duration_type& expiry_time)
{
    boost::optional<boost::system::error_code> timer_result;
    boost::asio::deadline_timer timer(s.get_io_service());
    timer.expires_from_now(expiry_time);
    timer.async_wait([&timer_result] (const boost::system::error_code& error) { timer_result.reset(error); });

    boost::optional<boost::system::error_code> read_result;
    boost::asio::async_read(s, buffers, [&read_result] (const boost::system::error_code& error, size_t) { read_result.reset(error); });

    s.get_io_service().reset();
    while (s.get_io_service().run_one())
    { 
        if (read_result)
            timer.cancel();
        else if (timer_result)
            s.cancel();
    }

    if (*read_result)
        throw boost::system::system_error(*read_result);
}

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