ASIO 处理程序参数和 boost::bind，编译时错误

Question

我正在为编译时错误而苦苦挣扎，尽我所能尝试，我看不出我做错了什么或与 documentation/examples 中所述的处理程序函数签名不同。（我在 Linux 上使用 Boost 1.41）

请帮我理解错误！（包含在下面作为片段）

我的应用程序有对象，其方法是 async_* 函数的处理程序。下面是代码片段。错误报告在标记为 "line 58" 的行中，我在其中使用 boost::bind

class RPC {

public:
    char recv_buffer[56];

    void data_recv (void) {
        socket.async_read_some (
                boost::asio::buffer(recv_buffer),
                boost::bind ( &RPC::on_data_recv, this, _1, _2 )
        );   // **<<==== this is line 58, that shows up in error listing**

        global_stream_lock.lock();
        std::cout << "[" << boost::this_thread::get_id()
            << "] data recvd" << std::endl;
        global_stream_lock.unlock();

    } // RPC::data_recv

    void on_data_recv (boost::system::error_code& ec, std::size_t bytesRx) {
        global_stream_lock.lock();
        std::cout << "[" << boost::this_thread::get_id()
            << "] bytes rcvd: " << std::endl;
        global_stream_lock.unlock();

        data_recv();  // call function that waits for more data

    } // RPC::on_data_recv

};  // RPC class def

有一个巨大的错误输出，但相关行似乎是：

../src/besw.cpp:58:   instantiated from here
/usr/include/boost/bind/bind.hpp:385: error: no match for call to ‘(boost::_m    fi::mf2<void, RPC, boost::system::error_code&, long unsigned int>) (RPC*&, boost::asio::error::basic_errors&, int&)’
/usr/include/boost/bind/mem_fn_template.hpp:272: note: candidates are: R boost::_mfi::mf2<R, T, A1, A2>::operator()(T*, A1, A2) const [with R = void, T = RPC, A1 = boost::system::error_code&, A2 = long unsigned int]
/usr/include/boost/bind/mem_fn_template.hpp:291: note:                R boost::_mfi::mf2<R, T, A1, A2>::operator()(T&, A1, A2) const [with R = void, T = RPC, A1 = boost::system::error_code&, A2 = long unsigned int]
make: *** [src/besw.o] Error 1

当我删除占位符（_1 和 _2）并且有一个没有参数的处理程序时，它会编译和执行而不会出错。这是修改后的代码片段。

    void data_recv (void) {
    socket.async_read_some (
            boost::asio::buffer(recv_buffer),
            boost::bind ( &RPC::on_data_recv, this )
    );

    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] data recvd" << std::endl;
    global_stream_lock.unlock();

} // RPC::data_recv

void on_data_recv (void) {
...
}

Answer 1

错误代码无法引用。按值或按 const&:

void on_data_recv(boost::system::error_code/* ec */, size_t /*bytes_transferred*/) {

另外，考虑使用 Asio 特定的占位符：

    socket.async_read_some(boost::asio::buffer(recv_buffer),
                           boost::bind(&RPC::on_data_recv, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));

还要使用适当的锁防护装置。我们在 C++ 中！使事情异常安全很容易，为什么不呢？

Live On Coliru

#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <iostream>

#include <boost/thread.hpp>

static boost::mutex global_stream_lock;

class RPC {
    char recv_buffer[56];
  public:

    void data_recv() {
        socket.async_read_some(boost::asio::buffer(recv_buffer),
                               boost::bind(&RPC::on_data_recv, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));

        boost::lock_guard<boost::mutex> lk(global_stream_lock);
        std::cout << "[" << boost::this_thread::get_id() << "] data recvd" << std::endl;
        global_stream_lock.unlock();
    }

    void on_data_recv(boost::system::error_code/* ec */, size_t /*bytes_transferred*/) {
        {
            boost::lock_guard<boost::mutex> lk(global_stream_lock);
            std::cout << "[" << boost::this_thread::get_id() << "] bytes rcvd: " << std::endl;
        }

        data_recv(); // call function that waits for more data
    }

    boost::asio::io_service service;
    boost::asio::ip::tcp::socket socket{service};
}; // RPC class def

int main() {}

ASIO 处理程序参数和 boost::bind，编译时错误

ASIO handler arguments and boost::bind, compile time error

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handler

boost-asio