setTimeout for Nashorn

settimeout-nashorn.js

// Adopted from here: https://gist.github.com/bripkens/8597903
// Makes ES7 Promises polyfill work on Nashorn https://github.com/jakearchibald/es6-promise
// (Haven't verified how correct it is, use with care)
(function(context) {
  'use strict';
 
  var Timer = Java.type('java.util.Timer');
  var Phaser = Java.type('java.util.concurrent.Phaser');

  var timer = new Timer('jsEventLoop', false);
  var phaser = new Phaser();
 
  var onTaskFinished = function() {
    phaser.arriveAndDeregister();
  };
 
  context.setTimeout = function(fn, millis /* [, args...] */) {
    var args = [].slice.call(arguments, 2, arguments.length);
 
    var phase = phaser.register();
    var canceled = false;
    timer.schedule(function() {
      if (canceled) {
        return;
      }
 
      try {
        fn.apply(context, args);
      } catch (e) {
        print(e);
      } finally {
        onTaskFinished();
      }
    }, millis);
 
    return function() {
      onTaskFinished();
      canceled = true;
    };
  };
 
  context.clearTimeout = function(cancel) {
    cancel();
  };
 
  context.setInterval = function(fn, delay /* [, args...] */) {
    var args = [].slice.call(arguments, 2, arguments.length);
 
    var cancel = null;
 
    var loop = function() {
      cancel = context.setTimeout(loop, delay);
      fn.apply(context, args);
    };
 
    cancel = context.setTimeout(loop, delay);
    return function() {
      cancel();
    };
  };
 
  context.clearInterval = function(cancel) {
    cancel();
  };
 
})(this);

This implementation looks incorrect to me. The java Timer.schedule() function invokes the specified function in a separate thread. This will result in JavaScript running in more than one concurrent thread, which creates race conditions, and violates the key JavaScript contract of asynchronous atomic callbacks.