* Fixed a race condition causing apiserver crashes during etcd healthchecking. ([#60069](https://github.com/kubernetes/kubernetes/pull/60069), [@wojtek-t](https://github.com/wojtek-t))

      long nanos = expirationNanos;
      long now = System.nanoTime();
      if (nanos == 0 || now - nanos >= 0) {
        synchronized (lock) {
          if (nanos == expirationNanos) { // recheck for lost race
            T t = delegate.get();
            value = t;
            nanos = now + durationNanos;
            // In the very unlikely event that nanos is 0, set it to 1;

    thread.join();
    // It's possible to race and suspend the thread just before the park call actually takes effect,
    // causing the thread to be suspended for 3.5 seconds, and then park itself for 2 seconds after
    // being resumed. To avoid a flake in this scenario, calculate how long that thread actually
    // waited and assert based on that time. Empirically, the race where the thread ends up waiting

				return
			}
		}
	}()
	return func(err error) {
		if doneCh == nil {
			return
		}

		// Indicate we are ready to write.
		doneCh <- err

		// Wait for channel to be closed so we don't race on writes.
		<-doneCh

		// Clear so we can be called multiple times without crashing.
		doneCh = nil
	}, &closeNotifier{rc: r.Body, done: bodyDoneCh}
}

    thread.join();
    // It's possible to race and suspend the thread just before the park call actually takes effect,
    // causing the thread to be suspended for 3.5 seconds, and then park itself for 2 seconds after
    // being resumed. To avoid a flake in this scenario, calculate how long that thread actually
    // waited and assert based on that time. Empirically, the race where the thread ends up waiting

some of the other birds tittered audibly.

  `What I was going to say,' said the Dodo in an offended tone,
`was, that the best thing to get us dry would be a Caucus-race.'

  `What IS a Caucus-race?' said Alice; not that she wanted much
to know, but the Dodo had paused as if it thought that SOMEBODY
ought to speak, and no one else seemed inclined to say anything.

    }

    @Override
    public void execute(Runnable task) {
      // If this operation was successfully cancelled already, calling the runnable will be a noop.
      // This also avoids a race where if outputFuture is cancelled, it will call taskFuture.cancel,
      // which will call newFuture.setFuture(oldFuture), to allow the next task in the queue to run

      monitor.enter();
      try {
        if (!transitioned) {
          // nothing has transitioned since construction, good.
          ready = true;
        } else {
          // This should be an extremely rare race condition.
          List<Service> servicesInBadStates = new ArrayList<>();
          for (Service service : servicesByState().values()) {
            if (service.state() != NEW) {

          source.skip(remainingByteCount)
          closeLater(ErrorCode.FLOW_CONTROL_ERROR)
          return
        }

        // Discard data received after the stream is finished. It's probably a benign race.
        if (finished) {
          source.skip(remainingByteCount)
          return
        }

        // Fill the receive buffer without holding any locks.

        // We reschedule ourselves with a lock held for two reasons. 1. we want to make sure that
        // cancel calls cancel on the correct future. 2. we want to make sure that the assignment
        // to currentFuture doesn't race with itself so that currentFuture is assigned in the
        // correct order.
        Throwable scheduleFailure = null;
        Cancellable toReturn;
        lock.lock();
        try {