将回调函数中的对象引用传递给 std::thread

Question

我正在尝试做这样的事情：

void commands_conn_handler(int socket, RPiServer& server) {
  // Not important code about handling connection
}

class RPiServer {
public:
  void Accept(void Accept(void (*acceped_conn_handler)(int, RPiServer&)) {
    // (...)
    int remote_socket = 0; // Doesn't matter - example.
    std::thread conn_handler_thread(acceped_conn_handler, remote_socket, *this);
    conn_handler_thread.join();
  }
};

int main() {
  RPiServer commands_server();
  commands_server.Accept(commands_conn_handler);
}

当我尝试构建它时，出现了一些错误：

In file included from /usr/include/c++/6/thread:39:0, from src/rpi_server/rpiserver.cpp:11: /usr/include/c++/6/functional: In instantiation of ‘struct std::_Bind_simple’: /usr/include/c++/6/thread:138:26: required from ‘std::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (*&)(int, RPiServer&); _Args = {int&, RPiServer&}]’ src/rpi_server/rpiserver.cpp:89:79: required from here /usr/include/c++/6/functional:1365:61: error: no type named ‘type’ in ‘class std::result_of’ typedef typename result_of<_Callable(_Args...)>::type result_type; ^~~~~~~~~~~ /usr/include/c++/6/functional:1386:9: error: no type named ‘type’ in ‘class std::result_of’ _M_invoke(_Index_tuple<_Indices...>) ^~~~~~~~~ Makefile:29: recipe for target 'build/rpi_server/rpiserver.o' failed

当我按以下方式更改线程函数时（删除对对象的引用）：

void commands_conn_handler(int socket) {
  // Not important code about handling connection
}

class RPiServer {
public:
  void Accept(void (*acceped_conn_handler)(int)) {
    // (...)
    int remote_socket = 0; // Doesn't matter - example.
    std::thread conn_handler_thread(acceped_conn_handler, remote_socket);
    conn_handler_thread.join();
  }
};

int main() {
  RPiServer commands_server();
  commands_server.Accept(commands_conn_handler);
}

一切都构建得很好。当我将引用作为参数传递给线程函数时我做错了什么？

Answer 1

所以这里有一个工作示例：

#include <thread>
#include <functional>
class RPiServer;

void commands_conn_handler(int socket, RPiServer &server) {
    // Not important code about handling connection
}

class RPiServer {
public:
    void Accept(void (*acceped_conn_handler)(int, RPiServer&)) {
        // (...)
        int remote_socket = 0; // Doesn't matter - example.
        std::thread conn_handler_thread(acceped_conn_handler, remote_socket, std::ref(*this));
        conn_handler_thread.join();
    }
};

int main() {
    RPiServer commands_server;
    commands_server.Accept(commands_conn_handler);
}

您遇到的错误是因为您没有为 conn_handler_thread 的构造函数提供正确的类型。要显式获取对对象的引用（您需要在此处执行此操作），请使用 std::ref() 函数。

P.S.: 此外，您复制粘贴了错误的代码示例，复制了 void Accept 部分。您在 main() 中也有 most vexing parse 错误。

将回调函数中的对象引用传递给 std::thread

Passing reference to object in callback function to std::thread

c++

multithreading

pthreads

c++11

stdthread