问题描述

我正在编写一个简单的 tcp 客户端来发送和接收单行文本.异步操作由 std::future 处理，以促进具有超时的阻塞查询.不幸的是，我的测试应用程序在破坏服务器对象时因访问冲突而崩溃.这是我的代码:

I am writing a simple tcp client to send and receive single lines of text. The asynchronous operations are handled by std::future in order to faciliate blocking queries with timeouts. Unfortunately, my test application crashes with an access violation when destructing the server object. Here is my code:

TCPClient.hpp

TCPClient.hpp

#ifndef __TCPCLIENT_H__
#define __TCPCLIENT_H__

#include <boost/asio.hpp>
#include <boost/asio/use_future.hpp>
#include <memory>
#include <vector>
#include <future>
#include <thread>
#include <chrono>
#include <iostream>
#include <iterator>

using namespace boost::asio;

class TCPClient {
public:
    TCPClient();
    ~TCPClient();

    void connect(const std::string& address, const std::string& port);
    void disconnect();

    std::string sendMessage(const std::string& msg);
private:
    boost::asio::io_service ioservice;
    boost::asio::io_service::work work;
    std::thread t;

    std::unique_ptr<boost::asio::ip::tcp::socket> socket;
};

inline TCPClient::TCPClient() : ioservice(), work(ioservice) {
    t = std::thread([&]() {
        try {
            ioservice.run();
        }
        catch (const boost::system::system_error& e) {
            std::cerr << e.what() << std::endl;
        }
    });
}

inline TCPClient::~TCPClient() {
    disconnect();
    ioservice.stop();
    if (t.joinable()) t.join();
}

inline void TCPClient::connect(const std::string& address, const std::string& port) {
    socket.reset(new ip::tcp::socket(ioservice));

    ip::tcp::resolver::query query(address, port);
    std::future<ip::tcp::resolver::iterator> conn_result = async_connect(*socket, ip::tcp::resolver(ioservice).resolve(query), use_future);

    if (conn_result.wait_for(std::chrono::seconds(6)) != std::future_status::timeout) {
        conn_result.get(); // throws boost::system::system_error if the operation fails
    }
    else {
        //socket->close();
        // throw timeout_error("Timeout");
        throw std::exception("timeout");
    }
}

inline void TCPClient::disconnect() {
    if (socket) {
        try {
            socket->shutdown(ip::tcp::socket::shutdown_both);
            std::cout << "socket points to " << std::addressof(*socket) << std::endl;
            socket->close();
        }
        catch (const boost::system::system_error& e) {
            // ignore
            std::cerr << "ignored error " << e.what() << std::endl;
        }
    }
}

inline std::string TCPClient::sendMessage(const std::string& msg) {
    auto time_over = std::chrono::system_clock::now() + std::chrono::seconds(4);

    /*
    // Doesn't affect the error
    std::future<size_t> write_fut = boost::asio::async_write(*socket, boost::asio::buffer(msg), boost::asio::use_future);

    try {
        write_fut.get();
    }
    catch (const boost::system::system_error& e) {
        std::cerr << e.what() << std::endl;
    }
    */
    boost::asio::streambuf response;

    std::future<std::size_t> read_fut = boost::asio::async_read_until(*socket, response, '
', boost::asio::use_future);
    if (read_fut.wait_until(time_over) != std::future_status::timeout) {
        std::cout << "read " << read_fut.get() << " bytes" << std::endl;
        return std::string(std::istreambuf_iterator<char>(&response), std::istreambuf_iterator<char>());
    }
    else {
        std::cout << "socket points to " << std::addressof(*socket) << std::endl;
        throw std::exception("timeout");
    }
}
#endif

main.cpp

#include <iostream>

#include "TCPClient.hpp"

int main(int argc, char* argv[]) {
    TCPClient client;
    try {
        client.connect("localhost", "27015");
        std::cout << "Response: " << client.sendMessage("Hello!") << std::endl;
    }
    catch (const boost::system::system_error& e) {
        std::cerr << e.what() << std::endl;
    }
    catch (const std::exception& e) {
        std::cerr << e.what() << std::endl;
    }
    system("pause");
    return 0;
}

输出是预期的超时"(测试服务器故意不发送数据)，但是ioservice.run()在TCPClient中关闭套接字后立即崩溃(访问冲突)::disconnect().我是不是在这里做一些内存管理不当?

The output is "timeout" as expected (test server sends no data on purpose), but ioservice.run() crashes immediately (access violation) after closing the socket in TCPClient::disconnect(). Am I doing some memory mismanagment here?

编译器是 MSVC 12.0.31101.00 Update 4 (Visual Studio 2013)

Compiler is MSVC 12.0.31101.00 Update 4 (Visual Studio 2013)

推荐答案

recvmsg 正在接收到一个缓冲区 (streambuf)，该缓冲区在 TCPClient::sendMessage(第 105 行，范围结束).

recvmsg is receiving into a buffer (streambuf) that was freed after throwing the exception in TCPClient::sendMessage (line 105, end of scope).

您忘记取消在第 97 行开始的异步操作 (async_read_until).修复它:

You forgot to cancel the asynchronous operation (async_read_until) started in line 97. Fix it:

else {
    socket->cancel(); // ADDED
    std::cout << "socket points to " << std::addressof(*socket) << std::endl;
    throw std::runtime_error("timeout");
}

甚至只是

    socket.reset(); // ADDED

其他超时路径也是如此.

Same goes for other timeout paths.

这篇关于boost::asio + std::future - 关闭套接字后访问冲突的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持跟版网！