Boost :: asio：端口在取消后第二次读取时自行取消

Question

我之前发布了一个非常相似的问题，但尚未完全回答。

（我试图反复读取一个串行端口，但我必须测试当电线断开时会发生什么。显然第一次它会按预期超时，但第二次端口似乎立即取消它自己的操作并将只是挂线。这是一个问题。

我在下面发布了代码。 有些行是来自我们日志系统的 LOG 行，请忽略它们，但这些行下的注释会说明日志是否触发。

我不知道为什么它会这样。 首先它只是触发计时器并取消端口，然后我再试一次，它立即用boost::error_code = 125取消端口

boost::asio::io_context io;
boost::asio::serial_port port;

std::size_t RS485CommunicationLayer::readUntil(std::vector<char>& buffer, char delim, std::chrono::microseconds timeout) {
    using boost::system::error_code;
    boost::optional<error_code> read_result;
    boost::optional<error_code> timer_result;
    size_t msglen = 0;
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: start"); 
// runs 1st and 2nd
    io.reset();

    boost::asio::system_timer timer(io, timeout);
    boost::asio::async_read_until(port, boost::asio::dynamic_buffer(buffer), delim, [&](error_code ec, size_t n) {
            if(!timer_result) {
                read_result = ec;
                timer.cancel();
                msglen = n;
                if(ec)
                    LOG_ERROR_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil() :: Error %s", ec.message().c_str());
// runs 2nd time only
            } // else canceled, do nothing
        }
    );
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: read action set");
    timer.async_wait([&](error_code ec) { 
        if (!read_result) {
            timer_result = ec;
            port.cancel();
            if(ec) {
                LOG_ERROR_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil() :: Timed out with error %s", ec.message().c_str());    
            } else {
                LOG_ERROR_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil() :: Timed out");
// runs 1st time only " RS485CommunicationLayer::readUntil() :: Error Operation canceled "
            }
            throw exception::read_exception(exception::read_exception::Code::TIME_OUT);
        } // else canceled, do nothing
    });
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: timer set : %d", static_cast<int>(timeout.count()));
    io.run();
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: ran");
// runs 1st time only
    if (read_result.get()) {
        std::stringstream sstream;
        sstream << read_result.get();
        LOG_ERROR_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: Port threw an error <message: %s>", sstream.str().c_str());
        throw exception::read_exception(exception::read_exception::Code::PORT, sstream.str());
    } 
    return msglen;
}

int main() {
//set up port options (baudrate etc)
for(size_t i = 0; i<10; i++) {
std::vector<char> buffer;
readUntil(buffer, '\', std::chrono::microseconds(1000));
}

}

Answer 1

我不应该从回调中抛出错误。 这将起作用：

std::size_t RS485CommunicationLayer::readUntil(std::vector<char>& buffer, char delim, std::chrono::microseconds timeout) {
    using boost::system::error_code;
    boost::optional<error_code> read_result {};
    boost::optional<error_code> timer_result {};
    size_t msglen = 0;
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: start");
    io.reset();

    boost::asio::system_timer timer(io, timeout);
    boost::asio::async_read_until(port, boost::asio::dynamic_buffer(buffer), delim, [&](error_code ec, size_t n) {
            if(!timer_result) {
                read_result = ec;
                timer.cancel();
                msglen = n;
            } // else canceled, do nothing
        }
    );
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: read action set");
    timer.async_wait([&](error_code ec) { 
        if (!read_result) {
            timer_result = ec;
            port.cancel();
        } // else canceled, do nothing
    });
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: timer set : %d", static_cast<int>(timeout.count()));

    io.run();
    LOG_INFO_FORMAT_IF(rS485CommunicationLayerLogger, "RS485CommunicationLayer::readUntil :: end");

    if(timer_result) {
        if(timer_result.get()) {
            LOG_ERROR_FORMAT_IF(rS485CommunicationLayerLogger, 
                "RS485CommunicationLayer::readUntil() :: Timed out with error %s", 
                timer_result.get().message().c_str()
            );
        } else {
            LOG_ERROR_FORMAT_IF(rS485CommunicationLayerLogger, 
                "RS485CommunicationLayer::readUntil() :: Timed out"
            );
        }
        throw exception::read_exception(exception::read_exception::Code::TIME_OUT);
    } else if(read_result && read_result.get()) {
        std::stringstream sstream;
        sstream << read_result.get();
        LOG_ERROR_FORMAT_IF(rS485CommunicationLayerLogger, 
            "RS485CommunicationLayer::readUntil :: Port threw an error <message: %s>", 
            sstream.str().c_str());
        throw exception::read_exception(exception::read_exception::Code::PORT, sstream.str());
    }
    return msglen;
   // TODO Maybe throw error in the completely unexpected case if no optional is populated
}