How do I exacute a block of code after the first of two threads finishes, no matter which one finishes first?

You probably want to use object.notify. Like this:

Object lock = new Object();
Thread t1 = new MyThread(lock);
Thread t2 = new MyThread(lock);

 synchronized (lock) { 
  t1.start();
  t2.start(); 
  lock.wait();
 }
// only reached after one thread has called lock.notify()
  ...


class MyThread extends Thread {
 Object lock;
 public MyThread(Object lock) {
  this.lock = lock;
 }
 public void run() {
  doThing();
  synchronized (lock) {
   lock.notify();
  }
 }
}

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