Question

I am trying to figure out how to eliminate a busy loop in a thread I have in Java. The thread does nothing but wait for a callback from the Listener class. The thread class looks something like this:

class MyThread implements Runnable, MessageListener{
  private Listen Listener;

  public MyThread(){
    Listener = new Listener(this);
  }

  public void run(){
    while(true){}
  }

  public void messageReceived(Message m){
    //do stuff
  }
}

I have tried to make this code as simple as possible. The idea is that Listener is waiting to receive some data from a serial port and when a message is received the thread will do some processing on it. I would prefer to use some synchronized variables such as a BlockingQueue of Message but I can’t modify the Listener code. The issue, of course, is that the run loop eats up processor cycles. My questions:

If I wait or sleep in the run loop will the function call still work as expected? (I’m not sure how to test that this works 100% of the time).

Is there some better way to avoid this loop altogether?

Answer 1

Do something like this

class MyThread implements Runnable, MessageListener{
          private Listen Listener;
          private Object lock = new Object();
      public MyThread(){
        Listener = new Listener(this);
      }

      public void run(){
        while(true){
            synchronized (lock) {
                try{
                    lock.wait();
                    // use the updated status
                }catch (Exception e) {
                    e.printStackTrace()
                }
            }
        }
      }

      public void messageReceived(Message m){
          synchronized (lock) {
                try{
                    // Do something with the message here like update some status
                    lock.notify();                      
                }catch (Exception e) {
                    e.printStackTrace()
                }

      }
    }

Once you get the event, you update some status/ store the message and release the notifying Thread. Then from your thread process the event