在服务于套接字连接的两个线程之间共享公共数据

Question

null

我所尝试的：（我想是愚蠢的）

• 我有一个public类，该对象应该作为public static共享，这样我就可以将其作为全局使用，而无需实例化它，例如MyGlobalClass.SharedMsg.
• 这不起作用，我无法将在一个线程中接收到的数据发送到另一个线程。

我知道有一个明显的锁定问题，因为如果一个线程正在写一个对象，其他线程不能访问它，直到第一个线程完成了写。

// Method of server class
public void startServer()
{
    if (!isRunning)
    {
        try
        {
            isRunning = true;
            while (isRunning)
            {
                try
                {
                    new ClientHandler(mysocketserver.accept()).start();
                }
                catch (SocketTimeoutException ex)
                {
                    //nothing to perform here, go back again to listening.
                }
                catch (SocketException ex)
                {
                    //Not to handle, since I'll stop the server using SocketServer's close() method, and its going to throw SocketException anyway.
                }
            }
        }
        catch (Exception ex)
        {
            ex.printStackTrace();
        }
    }
    else
        System.out.println("Server Already Started!");
}

和ClientHandler类。

public class ClientHandler extends Thread
{
    private Socket client = null;
    private ObjectInputStream in = null;
    private ObjectOutputStream out = null;

    public ClientHandler(Socket client)
    {
        super("ClientHandler");
        this.client = client;
    }

    //This run() is common for every Client that connects, and that's where the problem is.
    public void run()
    {
        try
        {
            in = new ObjectInputStream(client.getInputStream());
            out = new ObjectOutputStream(client.getOutputStream());

            //Message received from this thread.
            String msg = in.readObject().toString();
            System.out.println("Client @ "+ client.getInetAddress().getHostAddress() +" Says : "+msg);


            //Response to this client.
            out.writeObject("Message Received");

            out.close();
            in.close();
            client.close();
        }
        catch (Exception ex)
        {
            ex.printStackTrace();
        }
    }
}

我认为，我创建动态线程来为每个连接的客户机服务的方式（共享相同的数据源）不可能使用Global object，因为上面的run()对每个连接的客户机都是完全相同的，因此这个方法既是使用者也是生产者。我应该做什么修复，这样我就可以为每个连接创建动态线程，并仍然共享相同的对象。

Answer 1

您可能需要每个客户端之间的通信队列。每个队列将是数据从一个客户机推送到另一个客户机的“管道”。

您可以这样使用它（伪代码）：

Thread 1:
Receive request from Client A, with message for Client B
Put message on back of concurrent Queue A2B
Respond to Client A.

Thread 2:
Receive request from Client B.
Pop message from front of Queue A2B
Respond to Client B with message.

您可能还希望它是通用的，因此您有一个AllToB队列，许多客户机（因此也有许多线程）可以写入该队列。

null

1的例子：

public class ClientHandler extends Thread
{
  public static final Map<ClientHandler, BlockingQueue<String>> messageQueues 
    = new ConcurrentHashMap<>();

  <snip>

  public ClientHandler(Socket client)
  {
    super("ClientHandler");
    this.client = client;
    // Note: Bad practice to reference 'this' in a constructor.
    // This can throw an error based on what the put method does.
    // As such, if you are to do this, put it at the end of the method.
    messageQueues.put(this, new ArrayBlockingQueue<>());
  }

  // You can now access this in the run() method like so:
  // Get messages for the current client.
  // messageQueues.get(this).poll();
  // Send messages to the thread for another client.
  // messageQueues.get(someClient).offer(message);

几个注意事项：

• messageQueues对象应该真正包含客户端的某种标识符，而不是短期的对象引用。
• 可测试性更强的设计将messageQueues对象传递到构造函数中以允许模拟。
• 我可能建议为映射使用包装器类，这样您就可以使用2个参数调用offer，而不必担心映射语义。