无法从run方法中访问对象的属性（方法）！Java多线程

  • Z时代
  • 2024-01-10
  • 分类：问答

我在ServerConnectionManager中有以下代码：

public class ServerConnectionManager implements Runnable {
    private DatagramPacket receivedPacket;
    //some more things here
    public ServerConnectionManager(DatagramPacket receivedPacket){
        this.receivedPacket = receivedPacket;
        System.out.println("Connection manager has been assigned a request");
        System.out.println("The port of the request packet is "+receivedPacket.getPort());
         try {
             sendReceiveSocket = new DatagramSocket();
          } catch (SocketException se) {  
             se.printStackTrace();
             System.exit(1);
          }
    }
    @Override
    public void run() {
        //DEBUGGING LINES HERE
          System.out.println("The start method on connection manager works..");
          System.out.println("Point A");
          System.out.println("The port of the request packet is "+receivedPacket.getPort()); // the thread gets stuck here
          System.out.println("Does this work..?"); //This line never gets printed
          //some other stuff to be done here
                    }
         }

我在其他一些使用ServerConnectionManager的线程的run方法中有一些代码：让我们将此线程称为B

    @Override
    public void run() {
        while(true){
           try {        
                 System.out.println("Waiting..."); // so we know we're waiting
                 receiveSocket.receive(receivePacket);
              } catch (IOException e) {
                 System.out.print("Stopped Listening for some reason..");
                 //e.printStackTrace();
            }
            System.out.println("Server received something" );
           //Constructor of ServerConnectionManager
             ServerConnectionManager serverConnectionManager = new ServerConnectionManager(receivePacket);
             Thread managerThread = new Thread(serverConnectionManager, "connectionManager ");
             managerThread.start();
                 //some more stuff to be done
                }
        }

问题是我无法从ServerConnectionManager的run方法中调用ReceivedPacket上的任何方法。但是，我能够从此ServerConnectionManager线程的构造函数中调用receivedPacket.getPort（），它给了我预期的输出。但是它在run方法中没有任何作用。ServerConnectionManager打印的最后一行是“

Point A”。之后没有！！请检查我在该区域的DEBUGGING评论，以更好地了解我在说什么。

我知道我提供了很多代码。但是我根本无法理解问题。我尝试将其他参数（对象）从线程B传递到ServerConnectionManager的构造函数。而且我能够通过ServerConnectionManager的run方法访问它们。它只是receivedPacket不起作用…

回答：

DatagramPacket如果要启动新线程来处理它，则需要为每次接收创建一个新线程。否则，一个线程将在receive()另一线程尝试调用时在其上同步getPort()。该设计在任何情况下都是无效的，因为receive()在线程尝试处理它时，它将覆盖先前接收到的数据报中的所有内容。

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