[whatwg] workers

[Aaron Boodman]

I've reviewed and digested the latest workers update
(http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2008-August/015853.html).
I think we're converging :).

There are still a few improvements and simplifications I'd like to
see, however. With these (relatively minor) changes, I'd be really
happy with what we have.

* I think it was an interesting idea to have separate interfaces for
Dedicated and Shared workers, but in the end I don't think there's
enough difference between the two cases to justify it. I'd rather have
the total API surface be smaller, and generalize concepts as much as
possible. So...
  -  We should remove all the sendMessage/onmessage stuff from
DedicatedWorker, and just use the port convenience property.
  - We should move onconnect() up into WorkerGlobalScope

* Similarly, I'd like to rename startConversation() to connect(). I
think this aligns nicely with the onconnect event (connect() should
also trigger a 'connect' event inside the worker).

* I think it would be a nice convenience to have an onmessage event
inside workers that receives all messages sent to any port in the
worker.

* We have discussed having onerror expose runtime script errors that
happened inside the worker. I don't think this makes sense for shared
workers, so I propose that it be spec'd to only expose load errors.
Script errors can still be exposed via a global onerror property
inside the worker, and they can still be reported to the error
console. I don't think having script errors that happened inside a
worker be exposed outside it is that useful (load errors are useful,
though).

* I think onclose makes sense on Port instead of on Worker. The other
side of a Port can close out from under you, even if it is a window.

* Ojan brought this up earlier, but I don't think there should be
anything added to the global scope of workers except a single 'self'
object, which implements all the APIs that are available there.

* I still don't buy the utility of passing around MessagePorts, so I
suggest we table that for v2. It can always be added back later.


Here is an IDL sketch of what the API would look like after these changes...

OUTSIDE

interface MessagePort {
  EventListener onmessage;
  EventListener onclose; // if the other side goes away
  void sendMessage(in DOMString message);
}

interface Worker {
  EventListener onload;
  Port port; // convenience -- corresponds to the port available on
the created worker's WorkerContext object
  Port connect(); // the method previously known as "startConversation"
}

interface DedicatedWorker : Worker {
  void close();
}

INSIDE

// this is all exposed via "self"
interface WorkerContext {
  EventListener onclose;
  EventListener onmessage; // convenience -- receives all messages
sent to this worker, from any port
  // fired when the worker is first created, and for each additional
new SharedWorker() or connect() call
  EventListener onconnect;

  readonly String name;
  readonly MessagePort port; // convenience -- corresponds to the port
available on created Worker object

  void close();

  // + all the utils stuffs
}

CREATING WORKERS

var worker = new Worker(url);
var sharedWorker = new SharedWorker(name, url);


Let me know what you think!

- a