c++ - boost::asio不会触发读取处理程序，而wireshark看到数据进入

Question

我正在尝试发送一些数据并根据回复采取行动。我看到(使用wireshark)数据是由系统发送和接收的，但是boost::asio不会触发我的回调。有人知道我在做什么错吗？

#include <asio.hpp>
#include <bits/stdint-uintn.h>
#include <chrono>
#include <condition_variable>
#include <cstddef>
#include <iostream>
#include <memory>
#include <mutex>
#include <string>
#include <system_error>
#include <thread>

static const int polynomial = 0x1021; // represents x^16+x^12+x^5+1
uint16_t calc(uint8_t* bytes, std::size_t length)
{
  uint16_t new_crc = 0x0000;

  // bytes part
  for (std::size_t j = 0; j < length; ++j)
  {
    for (int i = 0; i < 8; ++i)
    {
      bool bit = ((bytes[j] >> (7 - i) & 1) == 1);
      bool c15 = ((new_crc >> 15 & 1) == 1);
      new_crc <<= 1;
      // If coefficient of bit and remainder polynomial = 1 xor crc with polynomial
      if (c15 ^ bit) new_crc ^= polynomial;
    }
  }

  return new_crc;
}

int main(int argc, const char* argv[])
{

  asio::io_service main_io_service;

  std::string ip = "192.168.100.155";
  int portP = 4001, portS = 4002;

  auto sPrimary = std::shared_ptr<asio::ip::tcp::socket>(new asio::ip::tcp::socket(main_io_service));
  auto sSecondary = std::shared_ptr<asio::ip::tcp::socket>(new asio::ip::tcp::socket(main_io_service));
  auto epPrimary = asio::ip::tcp::endpoint(asio::ip::address::from_string(ip), portP);
  auto epSecondary = asio::ip::tcp::endpoint(asio::ip::address::from_string(ip), portS);

  std::error_code ec;
  sPrimary->connect(epPrimary, ec);
  if (ec || !sPrimary->is_open())
  {
    std::cerr << "primary failed to connect" << std::endl;
  }

  ec.clear();
  sSecondary->connect(epSecondary, ec);
  if (ec || !sSecondary->is_open())
  {
    std::cerr << "secondary failed to connect" << std::endl;
  }

  std::mutex mutex;
  std::unique_lock<std::mutex> lock(mutex);
  std::condition_variable cv;

  const std::size_t msgSize = 9;
  uint8_t msg[msgSize];
  int i = 0;
  msg[i++] = 0x02;
  msg[i++] = 0xFF;
  msg[i++] = 0x00;
  msg[i++] = 0x00;
  msg[i++] = 0x00;
  msg[i++] = 0x00;

  uint16_t crc = calc(msg, i);

  msg[i++] = (uint8_t) (crc & 0xFF);
  msg[i++] = (uint8_t) (crc >> 8);
  msg[i++] = 0x03;

  const std::size_t buffSize = 1024;
  uint8_t buff[buffSize];
  std::size_t bytesRead = 0;

  asio::async_write((*sPrimary.get()), asio::buffer(msg, msgSize), [&sPrimary, &cv, &buff, &buffSize, &bytesRead](const std::error_code &ec, std::size_t bytesWritten)
  {
    asio::async_read((*sPrimary.get()), asio::buffer(buff, buffSize), [&cv, &bytesRead](const std::error_code &ec, std::size_t currentBytesRead)
    {
      bytesRead += currentBytesRead;
      cv.notify_one();
    });
  });

  main_io_service.run();

  cv.wait(lock);

  for (std::size_t i = 0; i < bytesRead; ++i)
    std::cout << std::hex << buff[i];

  main_io_service.stop();

  return 0;
}

刚刚添加了将要编译的整个测试代码。尽管您需要一个可以应答的设备。此代码与具有硬件的串行服务器进行通信，该硬件可对发送的数据包进行回复。

谢谢!

Answer 1

@ rafix07发出的问题是您的问题。

即使您通过在另一个线程上运行io_service::run()来“伪造”它，从技术上讲，您仍然具有相同竞争条件的时间窗口。

通常，锁定同步原语不会与基于任务的并行性混合使用。在这种情况下，您似乎只是想

读取完成后，

将另一个任务发布到服务

使您可以响应

的计时器到期

在代码非常简单的情况下，您甚至可以使用其他更简单的选项:

利用了run()阻塞直到所有处理程序完成的事实。也就是说，您可以将run()返回作为指示已完成读取的纯粹事实:

不使用异步处理程序，因为它没有作用(这可能归因于此处过于简单的示例代码)

4.使用同步IO

到目前为止，这是最简单的。整个程序进行了许多其他简化

Live On Coliru

#include <cstdint>
#include <iostream>
#include <string>

#ifndef NOBOOST
    #include <boost/asio.hpp>
    namespace asio = boost::asio;
    using boost::system::error_code;
#else
    #include <asio.hpp>
    namespace asio = boost::asio;
    using std::error_code;
#endif

static const int polynomial = 0x1021; // represents x^16+x^12+x^5+1
uint16_t calc_crc(uint8_t* bytes, std::size_t length) {
    uint16_t new_crc = 0x0000;

    // bytes part
    for (std::size_t j = 0; j < length; ++j) {
        for (int i = 0; i < 8; ++i) {
            bool bit = ((bytes[j] >> (7 - i) & 1) == 1);
            bool c15 = ((new_crc >> 15 & 1) == 1);
            new_crc <<= 1;
            // If coefficient of bit and remainder polynomial = 1 xor crc with polynomial
            if (c15 ^ bit)
                new_crc ^= polynomial;
        }
    }

    return new_crc;
}

int main() {
    static const std::string ip = "127.0.0.1";
    static const unsigned short portP = 4001, portS = 4002;

    using asio::ip::address;

    asio::io_service io;
    asio::ip::tcp::socket sPrimary(io), sSecondary(io);

    sPrimary.connect({ address::from_string(ip), portP });
    sSecondary.connect({ address::from_string(ip), portS });

    uint8_t msg[] {
        0x02, 0xFF, 0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, //crc
        0x03
    };

    {   // set crc
        uint16_t const crc = calc_crc(msg, sizeof(msg)-3);
        msg[sizeof(msg)-3] = (uint8_t)(crc & 0xFF);
        msg[sizeof(msg)-2] = (uint8_t)(crc >> 8);
    }

    std::string buff;

    auto bytesWritten = asio::write(sPrimary, asio::buffer(msg));
    std::cout << bytesWritten << " sent" << std::endl;
    auto bytesRead    = asio::read(sPrimary, asio::dynamic_buffer(buff), asio::transfer_exactly(32));
    std::cout << bytesRead << " received" << std::endl;

    for (uint8_t ch : buff)
        std::cout << std::hex << static_cast<int>(ch);
    std::cout << std::endl;
}

版画

9 sent
32 received
23696e636c756465203c63737464696e743ea23696e636c756465203c696f73

实际上，这就是 main.cpp的前32个字节的十六进制编码

3.使用隐式补全

如果 run()返回，请相信处理程序已运行(需要进行错误处理)。代码本质上是相同的，但是对lambda捕获和对象生存期有更详尽的考虑。

Note: all other simplifications still apply

Live On Coliru

asio::async_write(sPrimary, asio::buffer(msg), [&sPrimary, &buff](error_code ec, size_t bytesWritten) {
    std::cout << "async_write: " << ec.message() << ", " << bytesWritten << " sent" << std::endl;
    asio::async_read(sPrimary, asio::dynamic_buffer(buff), asio::transfer_exactly(32), [](error_code ec, size_t bytesRead) {
        std::cout << "async_read: " << ec.message() << ", " << bytesRead << " received" << std::endl;
    });
});

io.run();

for (uint8_t ch : buff)
    std::cout << std::hex << static_cast<int>(ch);
std::cout << std::endl;

打印品:

async_write: Success, 9 sent
async_read: Success, 32 received
23696e636c756465203c63737464696e743ea23696e636c756465203c696f73

2.使用计时器信号

通过使用计时器对象表示条件，这与您的CV方法最“相似”。

尤其是，它的错误处理比上面的“3”更好。代码

还请注意

，它保证调用signal_complete的完成处理程序(除非程序过早终止)

这样，信息在计时器的expiry()中，而不在错误代码中(时间将始终显示为已取消)

Live On Coliru

std::string buff;
asio::high_resolution_timer signal_complete(io, std::chrono::high_resolution_clock::time_point::max());
signal_complete.async_wait([&signal_complete, &buff](error_code ec) {
     std::cout << "signal_complete: " << ec.message() << std::endl;

     if (signal_complete.expiry() < std::chrono::high_resolution_clock::now()) {
        for (uint8_t ch : buff)
            std::cout << std::hex << static_cast<int>(ch);
        std::cout << std::endl;
     }
});

asio::async_write(sPrimary, asio::buffer(msg), [&sPrimary, &buff, &signal_complete](error_code ec, size_t bytesWritten) {
    std::cout << "async_write: " << ec.message() << ", " << bytesWritten << " sent" << std::endl;
    asio::async_read(sPrimary, asio::dynamic_buffer(buff), asio::transfer_exactly(32), [&signal_complete](error_code ec, size_t bytesRead) {
        std::cout << "async_read: " << ec.message() << ", " << bytesRead << " received" << std::endl;

        if (!ec) {
            signal_complete.expires_at(std::chrono::high_resolution_clock::time_point::min());
        } else {
            signal_complete.cancel();
        }
    });
});

io.run();

打印品:

async_write: Success, 9 sent
async_read: Success, 32 received
signal_complete: Operation canceled
23696e636c756465203c63737464696e743ea23696e636c756465203c696f73

1.阅读完成后发布另一个任务

这最适合大多数异步IO场景，因为它将所有任务放在同一队列中。

唯一更复杂的部分是正确设置(共享)对象的生存时间。

Live On Coliru

std::string buff;

asio::async_write(sPrimary, asio::buffer(msg), [&io, &sPrimary, &buff](error_code ec, size_t bytesWritten) {
    std::cout << "async_write: " << ec.message() << ", " << bytesWritten << " sent" << std::endl;
    asio::async_read(sPrimary, asio::dynamic_buffer(buff), asio::transfer_exactly(32), [&io, &buff](error_code ec, size_t bytesRead) {
        std::cout << "async_read: " << ec.message() << ", " << bytesRead << " received" << std::endl;

        if (!ec) {
            post(io, [&buff] {
                for (uint8_t ch : buff)
                    std::cout << std::hex << static_cast<int>(ch);
                std::cout << std::endl;
            });
        }
    });
});

io.run();

再次打印:

async_write: Success, 9 sent
async_read: Success, 32 received
23696e636c756465203c63737464696e743ea23696e636c756465203c696f73