C++在地图中使用emplace()时阻止析构函数调用

Question

我有一个管理资源的类(网络套接字).

我编写了一个类ConnectionHandler来处理通过调用创建的网络套接字accept().

这个类在设计时考虑了RAII,当accept()调用时,返回的套接字放入a ConnectionHandler,当这超出范围时,析构函数关闭套接字.

我也ConnectionHandler通过将它们保存在地图中来跟踪我所有的打开(将套接字地址(IP:端口)映射到ConnectionHandler与该地址对应的地址).

我有一个问题,"将这些ConnectionHandler"放入地图".

我已经做到了这样一个ConnectionHandler无法复制(至少我相信我已经这样做了),但是在调用时,调用std::map::emplace了ConnectionHandler析构函数(可能是为了删除在该行某处创建的临时对象)和套接字已关闭.

如您所见,这会产生问题,因为现在套接字无法在程序中进一步使用.

我有什么方法可以阻止ConnectionHandler在将它驱逐到一个被破坏者的时候被叫出来std::map？

这是ConnectionHandler:头文件的代码:

class ConnectionHandler
{
    private:
        constexpr static long BUFFER_SIZE = 1 << 12;    // 4K Buffer

        SocketAddress peer;             // This is kept around to be able to produce clear exception messages when something goes wrong
        SocketFileDescriptor socket;    // using SocketFileDescriptor = int;

    public:
        ConnectionHandler() noexcept = delete;                                      // Default Constructor

        explicit ConnectionHandler(SocketFileDescriptor socket, const SocketAddress& socketAddress) noexcept;   // Value Constructor

        ConnectionHandler (ConnectionHandler&& handler) noexcept;                   // Move Constructor

        ConnectionHandler (const ConnectionHandler& handler) = delete;              // Delete Copy Constructor

        ConnectionHandler& operator= (ConnectionHandler&& handler) noexcept;        // Move Assignment Operator

        ConnectionHandler& operator= (const ConnectionHandler& handler) = delete;   // Delete Copy Assignment Operator

        ~ConnectionHandler();                                                       // Destructor

        void close() noexcept;                                                      // Allow the owner to manually close the socket if necessary

        void set_blocking (bool blocking) const;                                    // Make the socket either blocking or non-blocking

        friend std::ostream& operator<< (std::ostream& stream, const ConnectionHandler& handler);   // Receive data from the socket

        friend std::istream& operator>> (std::istream& stream, const ConnectionHandler& handler);   // Send data to the socket
};

并实施:

ConnectionHandler::ConnectionHandler(SocketFileDescriptor socket, const SocketAddress& socketAddress) noexcept: peer(socketAddress), socket(socket)
{
}

ConnectionHandler::ConnectionHandler(ConnectionHandler&& handler) noexcept: peer(std::move(handler.peer)), socket(handler.socket)
{
}

ConnectionHandler& ConnectionHandler::operator=(ConnectionHandler&& handler) noexcept
{
    this->peer = std::move(handler.peer);
    this->socket = handler.socket;
    return *this;
}

ConnectionHandler::~ConnectionHandler()
{
    if (this->socket > 0)   //  Check if the socket has been closed manually
                            //  Don't bother setting the socket to -1, the object is being destroyed anyway
    {
        std::cout << "Closing socket from destructor " << this->socket << std::endl;
        ::close(this->socket);
    }
}

void ConnectionHandler::close() noexcept
{
    std::cout << "Closing socket from close() " << this->socket << std::endl;   // Close the socket manually and indicate it is closed by setting it's value to -1
    ::close(this->socket);
    this->socket = -1;
}

[...]

这就是SocketAddress类的样子(对于IPv6不起作用,我知道):

class SocketAddress
{
    private:
        std::array<std::uint8_t, 4> ip;
        std::uint16_t port;

    public:
        friend void swap (SocketAddress& sa1, SocketAddress& sa2) noexcept;

        SocketAddress() noexcept;

        explicit SocketAddress(struct sockaddr_storage* sockaddrStorage);

        SocketAddress (const SocketAddress& address) = default;

        SocketAddress (SocketAddress&& address) noexcept = default;

        SocketAddress& operator= (SocketAddress address);

        friend bool operator< (const SocketAddress& lhs, const SocketAddress& rhs) noexcept;

        friend std::string to_string(const SocketAddress& address) noexcept;
};

最后,这是创建ConnectionHandler并将其放在地图中的代码:

void Server::listenLoop()   // acceptLoop() would be a better name
{

    struct sockaddr_storage remoteAddr;

    while(!stop)    // stop is a std::atomic<bool>
    {
        [...]   // accept() connections in a loop

        SocketAddress address = SocketAddress(&remoteAddr);
        this->incomingSockets.emplace(std::make_pair(address, ConnectionHandler(childFileDesc, address)));
    }

    [...]
}

此函数在与主线程分开的线程上运行,线程保存在Server对象中,并在Server对象的析构函数中连接.

Answer 1

在移动构造函数/赋值运算符中,您需要使移动的对象无效.仍然会在从对象移动时调用析构函数.如果它们的套接字不为0,则析构函数仍将在fd上调用close.