The Ashes

Alex Fritze has introduced Stratified JavaScript, an experiment that allows us to play with some concurrency features in JavaScript in a cross browser way.

It features:

The ability to pause execution: hold()

PLAIN TEXT

JAVASCRIPT:

1.  
2.  var elem = document.getElementById(“animated_element”);
3.   var x = 0;
4.   while (true) {
5.     elem.style.left = x;
6.     x = (x + 10) % 200;
7.     hold(100);
8.   }
9.  

Fork-Join Parallelism

PLAIN TEXT

JAVASCRIPT:

1.  
2.  function animate(elemname, duration_ms, step_ms) {
3.     var elem = document.getElementById(elemname);
4.     var start_time = new Date();
5.     var x = 0;
6.     do {
7.       elem.style.left = x;
8.       x = (x + 10) % 200;
9.       hold(step_ms);
10.     } while (duration_ms> new Date() – start_time);
11.   }
12.  
13.   function par(a, b) {
14.     alert(“all done”);
15.   }
16.  
17.   par(animate(“animated_element_1”, 10000, 100),
18.       animate(“animated_element_2”, 7000, 80));
19.  

Exploratory parallelism

PLAIN TEXT

JAVASCRIPT:

1.  
2. animate(“animated_element_1”, 10000, 100) @
3. animate(“animated_element_2”, 7000, 80);
4.  
5. alert(“all done”);
6.  

Suspend/Resume

PLAIN TEXT

JAVASCRIPT:

1.  
2. function waitForEvent(event, elem) {
3.     suspend {
4.       var rv;
5.       var listener_func = function(e) {
6.         rv = e;
7.         resume();
8.       };
9.       elem.addEventListener(event, listener_func, false);
10.     }
11.     finally {
12.       elem.removeEventListener(event, listener_func, false);
13.     }
14.     return rv;
15. }
16.  

Under the hood, Stratified JavaScript is executed by a runtime based on Oni.

Kris Zyp asked for a comparison to Narrative JavaScript or JavaScript strands and Alex came back with:

The most important enhancement of SJS versus Narrative JavaScript or Strands is the support for ‘exploratory parallelism’ or ‘parallel selection’, as embodied by SJS’s Alt operator (‘@’). There are many problems that are tricky to express with just threads, but which can be expressed elegantly in a structured, compositional way with the use of Alt.