Flag Communication : synchronized « Thread « Java Tutorial

1. Java Tutorial
2. Thread
3. synchronized

public class FlagComm {
  public static void main(String args[]) {
    FlagSend s = new FlagSend();
    FlagRec r = new FlagRec(s);
    Thread st = new Thread(s);
    Thread rt = new Thread(r);
    rt.setDaemon(true); 
    st.start();
    rt.start();
    try {
      while (s.isValid) { 
        Thread.sleep(100);
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

class FlagSend implements Runnable {
  volatile int theValue;

  volatile boolean isValid;

  public void run() {
    for (int i = 0; i < 5; i++) {
      while (isValid) {
        Thread.yield();
      }
      theValue = (int) (Math.random() * 256);
      System.out.println("sending " + theValue);
      isValid = true;
    }
  }
}

class FlagRec implements Runnable {
  FlagSend theSender;

  public FlagRec(FlagSend sender) {
    theSender = sender;
  }

  public void run() {
    while (true) {
      while (!theSender.isValid) {
        Thread.yield();
      }
      System.out.println("received " + theSender.theValue);
      theSender.isValid = false;
    }
  }
}