Question

If I have the following dummy code:

public static void main(String[] args) {
  TestRunnable test1 = new TestRunnable();
  TestRunnable test2 = new TestRunnable();
  Thread thread1 = new Thread(test1);
  Thread thread2 = new Thread(test2);
  thread1.start();
  thread2.start();
}

public static class TestRunnable implements Runnable {
  @Override
  public void run() {
    while(true) {
      //bla bla
    }
  }
}

In my current program I have a similar structure i.e. two threads executing the same Run() method. But for some reason only thread 1 is given CPU time i.e. thread 2 never gets a chance to run. Is this because while thread 1 is in its while loop , thread 2 waits?

I’m not exactly sure, if a thread is in a while loop is it “blocking” other threads? I would think so, but not 100% sure so it would be nice to know if anyone could inform me of what actually is happening here.

EDIT
Okay, just tried to make a really simple example again and now both threads are getting CPU time. However this is not the case in my original program. Must be some bug somewhere. Looking into that now. Thanks to everyone for clearing it up, at least I got that knowledge.

Answer 1

There is no guarantee by the JVM that it will halt a busy thread to give other threads some CPU.

It’s good practice to call Thread.yield();, or if that doesn’t work call Thread.sleep(100);, inside your busy loop to let other threads have some CPU.