static Thread startThreadRegisteredInCollection(Cl<Thread> collection, S name, Runnable r) {
  if (r == null) null;
  Thread t = newThread(name, r {
    try {
      r.run();
    } finally {
      remove(collection, currentThread());
    }
  });
  add(collection, t);
  startThread(t);
  ret t;
}