调用std :: bind乘积后意外调用析构函数

Question

有一个使用boost::asio::io_context的简单示例

https://github.com/unegare/boost-ex/blob/500e46f4d3b41e2abe48e2deccfab39d44ae94e0/main.cpp

    #include <boost/asio.hpp>
    #include <boost/beast/core.hpp>
    #include <boost/beast/http.hpp>
    #include <boost/beast/version.hpp>
    #include <thread>
    #include <vector>
    #include <memory>
    #include <mutex>
    #include <chrono>
    #include <iostream>
    #include <exception>

    std::mutex m_stdout;

    class MyWorker {
      std::shared_ptr<boost::asio::io_context> io_context;
      std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> work_guard;
    public:
      MyWorker(std::shared_ptr<boost::asio::io_context> &_io_context, std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> &_work_guard):
        io_context(_io_context), work_guard(_work_guard) {}
      MyWorker(const MyWorker &mw): io_context(mw.io_context), work_guard(mw.work_guard) {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] MyWorker copy constructor" << std::endl;
        m_stdout.unlock();
      }
      MyWorker(MyWorker &&mw): io_context(std::move(mw.io_context)), work_guard(std::move(mw.work_guard)) {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] MyWorker move constructor" << std::endl;
        m_stdout.unlock();
      }
      ~MyWorker() {}

      void operator() () {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] Thread Start" << std::endl;
        m_stdout.unlock();

        while(true) {
          try {
            boost::system::error_code ec;
            io_context->run(ec);
            if (ec) {
              m_stdout.lock();
              std::cout << "[" << std::this_thread::get_id() << "] MyWorker: received an error: " << ec << std::endl;
              m_stdout.unlock();
              continue;
            }
            break;
          } catch (std::exception &ex) {
            m_stdout.lock();
            std::cout << "[" << std::this_thread::get_id() << "] MyWorker: caught an exception: " << ex.what() << std::endl;
            m_stdout.unlock();
          }
        }

        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] Thread Finish" << std::endl;
        m_stdout.unlock();
      }
    };

    class Client: public std::enable_shared_from_this<Client> {
      std::shared_ptr<boost::asio::io_context> io_context;
      std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> work_guard;
      std::shared_ptr<boost::asio::ip::tcp::socket> sock;
      std::shared_ptr<std::array<char, 512>> buff;
    public:
      Client(std::shared_ptr<boost::asio::io_context> &_io_context, std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> &_work_guard, std::shared_ptr<boost::asio::ip::tcp::socket> &_sock):
        io_context(_io_context), work_guard(_work_guard), sock(_sock) {
        buff = std::make_shared<std::array<char,512>>();
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " with args" << std::endl;
        m_stdout.unlock();
      }
      Client(const Client &cl): io_context(cl.io_context), work_guard(cl.work_guard), sock(cl.sock), buff(cl.buff) {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " copy" << std::endl;
        m_stdout.unlock();
      }
      Client(Client &&cl): io_context(std::move(cl.io_context)), work_guard(std::move(cl.work_guard)), sock(std::move(cl.sock)), buff(std::move(cl.buff)) {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " move" << std::endl;
        m_stdout.unlock();
      }
      ~Client() {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << " buff.use_count: " << buff.use_count() << " | sock.use_count: " << sock.use_count() << " | io_context.use_count: " << io_context.use_count() << std::endl;
        m_stdout.unlock();
      }

      void OnConnect(const boost::system::error_code &ec) {
        std::cout << __FUNCTION__ << std::endl;
        if (ec) {
          m_stdout.lock();
          std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << ": " << ec << std::endl;
          m_stdout.unlock();
        } else {
    //      buff = std::make_shared<std::array<char, 512>>();
          char req[] = "GET / HTTP/1.1\r\nHost: unegare.info\r\n\r\n";
          memcpy(buff->data(), req, strlen(req));
          m_stdout.lock();
          std::cout << req << std::endl;
          m_stdout.unlock();
          sock->async_write_some(boost::asio::buffer(buff->data(), strlen(buff->data())), std::bind(std::mem_fn(&Client::OnSend), this, std::placeholders::_1, std::placeholders::_2));
        }
        std::cout << __FUNCTION__ << " use_count: " << buff.use_count() << std::endl;
      }

      void OnSend(const boost::system::error_code &ec, std::size_t bytes_transferred) {
        std::cout << __FUNCTION__ << " use_count: " << io_context.use_count() << std::endl;
        if (ec) {
          m_stdout.lock();
          std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << ": " << ec << std::endl;
          m_stdout.unlock();
        } else {
        std::cout << __FUNCTION__ << " use_count: " << buff.use_count() << std::endl;
          buff->fill(0);
        std::cout << __FUNCTION__ << std::endl;
          sock->async_read_some(boost::asio::buffer(buff->data(), buff->size()), std::bind(std::mem_fn(&Client::OnRecv), this, std::placeholders::_1, std::placeholders::_2));
        }
      }

      void OnRecv(const boost::system::error_code &ec, std::size_t bytes_transferred) {
        std::cout << __FUNCTION__ << std::endl;
        if (ec) {
          m_stdout.lock();
          std::cout << "[" << std::this_thread::get_id() << "] " << __FUNCTION__ << ": " << ec << std::endl;
          m_stdout.unlock();
        } else {
          m_stdout.lock();
          std::cout << buff->data() << std::endl;
          m_stdout.unlock();
        }
      }
    };

    int main () {
      std::shared_ptr<boost::asio::io_context> io_context(std::make_shared<boost::asio::io_context>());
      std::shared_ptr<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> work_guard(
        std::make_shared<boost::asio::executor_work_guard<boost::asio::io_context::executor_type>> (boost::asio::make_work_guard(*io_context))
      );
      MyWorker mw(io_context, work_guard);
      std::vector<std::thread> vth;
      vth.reserve(1);
      for (int i = 1; i > 0; --i) {
        vth.emplace_back(mw);
      }
      std::shared_ptr<Client> cl = 0;
      try {
        boost::asio::ip::tcp::resolver resolver(*io_context);
        boost::asio::ip::tcp::resolver::query query("unegare.info", "80");
        boost::asio::ip::tcp::endpoint ep = *resolver.resolve(query);
        m_stdout.lock();
        std::cout << "ep: " << ep << std::endl;
        m_stdout.unlock();

        std::shared_ptr<boost::asio::ip::tcp::socket> sock(std::make_shared<boost::asio::ip::tcp::socket>(*io_context));
        std::shared_ptr<Client> cl2(std::make_shared<Client>(io_context, work_guard, sock));
        cl = cl2->shared_from_this();
        m_stdout.lock();
        std::cout << "HERE: use_count = " << cl.use_count() << std::endl;
        m_stdout.unlock();
        sock->async_connect(ep, std::bind(std::mem_fn(&Client::OnConnect), *cl2->shared_from_this(), std::placeholders::_1));
        std::this_thread::sleep_for(std::chrono::duration<double>(1));
        m_stdout.lock();
        std::cout << "AFTER CALL" << std::endl;
        m_stdout.unlock();
    //    asm volatile ("");
      } catch (std::exception &ex) {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] Main Thread: caught an exception: " << ex.what() << std::endl;
        m_stdout.unlock();
      }
      try {
        char t;
        std::cin >> t;
        work_guard->reset();
    //    std::this_thread::sleep_for(std::chrono::duration<double>(1));
    //    std::cout << "Running" << std::endl;
    //    io_context->run();
      } catch (std::exception &ex) {
        m_stdout.lock();
        std::cout << "[" << std::this_thread::get_id() << "] Main Thread: caught an exception: " << ex.what() << std::endl;
        m_stdout.unlock();
      }
      std::for_each(vth.begin(), vth.end(), std::mem_fn(&std::thread::join));
      return 0;
    }

stdout：

[140487203505984] MyWorker copy constructor
[140487203505984] MyWorker move constructor
[140487185372928] Thread Start
ep: 95.165.130.37:80
[140487203505984] Client with args
HERE: use_count = 2
[140487203505984] Client copy
[140487203505984] Client move
[140487203505984] ~Client buff.use_count: 0 | sock.use_count: 0 | io_context.use_count: 0
[140487185372928] Client move
[140487185372928] ~Client buff.use_count: 0 | sock.use_count: 0 | io_context.use_count: 0
OnConnect
GET / HTTP/1.1
Host: unegare.info


OnConnect use_count: 2
[140487185372928] ~Client buff.use_count: 2 | sock.use_count: 3 | io_context.use_count: 5
Segmentation Fault (core dumped)

但是由于对Client对象的错误引用而导致的段错误理解有些问题。

但是我不明白为什么cl2在调用之后会被破坏>

sock->async_connect(ep, std::bind(std::mem_fn(&Client::OnConnect), *cl2->shared_from_this(), std::placeholders::_1));
在162行。

以及...为什么要调用复制构造函数？正如从上面的stdout中可能注意到的。

[有一个使用boost :: asio :: io_context https://github.com/unegare/boost-ex/blob/500e46f4d3b41e2abe48e2deccfab39d44ae94e0/main.cpp #include ...

Answer 1

您不会随输出跟踪cl2的销毁：cl2为std::shared_ptr<Client>。您似乎在跟踪Client对象的构造。

Answer 2

您尝试理解的好处。但是，从简单开始！