ButtonRace.java

import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.LongAdder;
import java.util.stream.Stream;

import static java.lang.Thread.sleep;
import static java.util.Arrays.asList;
import static java.util.Collections.emptyList;
import static java.util.stream.Collectors.toList;

public class ButtonRace {

  public static void main(String[] args) throws InterruptedException {
    Button ok = new Button("OK", () -> System.out.println("TASK: OK"));
    Button cancel = new Button("CANCEL", () -> System.out.println("TASK: CANCEL"));

//    Button ok = new Button("OK");
//    Button cancel = new Button("CANCEL");

    CountDownLatch start = new CountDownLatch(1);
    List<Thread> threads = Stream.of(ok, cancel).map(button -> new Thread(() -> {
      try {
        start.await();
        while (!Thread.currentThread().isInterrupted()) {
          button.click();
        }
      } catch (Exception ignored) {
      }
    })).collect(toList());
    threads.forEach(Thread::start);
    start.countDown();

    sleep(5_000);
    threads.forEach(Thread::interrupt);
    for (Thread thread : threads) {
      thread.join();
    }

    System.out.println(ok);
    System.out.println(cancel);
  }

  public static class Button {
    private final String name;

    private final List<Runnable> tasks;
    private final LongAdder clicks = new LongAdder();

    public Button(String name) {
      this.name = name;
      this.tasks = emptyList();
    }

    public Button(String name, Runnable... runnable) {
      this.name = name;
      this.tasks = asList(runnable);
    }

    public void click() {
      clicks.increment();
      synchronized (tasks) {
        //System.out.println("Clicking(" + this + ")");
        doingSomeWork();
        tasks.forEach(Runnable::run);
        //System.out.println("Clicked(" + this + ")");
      }
    }

    // [...]

    @Override
    public String toString() {
      return name + ": " + clicks + " clicks";
    }

    private void doingSomeWork() {
      try {
        sleep(100);
      } catch (InterruptedException e) {
        throw new RuntimeException(e);
      }
    }
  }

}