Kumpera.java

import java.util.*;
import java.util.concurrent.*;
import java.util.function.*;

class EWC {
	private Consumer<Object> tarefinha;

	private Queue<Object> waiters = new ConcurrentLinkedQueue<>();

	public void wait(Object arg) { 
		Object lock = new Object();
		synchronized(this) {
			waiters.add(lock);
		}

		synchronized(lock) {	
			try {
				System.out.println("esperando " + lock);
				lock.wait();
				System.out.println("recebido " + lock);
			} catch(InterruptedException e) {}	

			if(tarefinha != null) {
				tarefinha.accept(arg);				
			}
		}
	}
	public void pulse (Consumer<Object> callback) {
		Object w;
		synchronized(this) {
			w = waiters.poll();
			System.out.println("removendo" + w);
			this.tarefinha = callback;
		}
		synchronized(w) {
			w.notify();
			System.out.println("notificado" + w);
		}
	}

	public void pulseAll (Consumer<Object> callback) {
		List<Object> waitersCopy;
		synchronized(this) {
			waitersCopy = new ArrayList<>(waiters);
			this.tarefinha = callback;
			waiters.clear();
		}

		for(Object w : waitersCopy) {
			synchronized(w) {
				w.notifyAll();
			}
		}
		
	}
}

class Kumpera {
	public static void main(String ... args) throws Exception {
		final EWC ewc = new EWC();
		new Thread(() -> ewc.wait("paulo")).start();
		new Thread(() -> ewc.wait("silveira")).start();

		Thread.sleep(100);
		new Thread(() -> ewc.pulse(System.out::println)).start();

		Thread.sleep(100);
		new Thread(() -> ewc.wait("kumpera")).start();
		new Thread(() -> ewc.pulseAll(System.out::println)).start();
	}
}