Do web workers use actor model?

Question

I have been trying to understand how actor model and web workers work.

In https://dzone.com/articles/html5-web-workers-classic: "Web Workers provide a message-passing model, where scripts can communicate only through well-defined immutable messages, do not share any data, and do not use synchronization mechanisms for signaling or data integrity."

To me, it sounds very similar to actor model. Is there a difference?

UPDATE: According to Benjamin Erb:

" The fundamental idea of the actor model is to use actors as concurrent primitives that can act upon receiving messages in different ways:

1.Send a finite number of messages to other actors.
2. Spawn a finite number of new actors.
3. Change its own internal behavior, taking effect when the next incoming message is handled."

The first two apply, but how about the last one?

Answer 1

Yes, actor model quite describes how do the workers work. However actor model has some more abstract requirements that also depend on your implementation - but I recommend complying with the actor model. You can read the full article on Wikipedia.

There's one thing I'd like to point out to you though:

No requirement on order of message arrival

This is something that depends on your implementation and I strongly recommend to comply with this requirement. This means, for example, if sending data in chunks, give chunks indexes. Worker messages arrive in the order they're sent, but it's good not to rely on that once your code becomes complicated.

Change its own internal behavior, taking effect when the next incoming message is handled (as per your "update")

This point kinds conflicts with the previous one. But anyone who at least read some web workers tutorial, the answer is obvious: Yes, worker can do that. Consider following code:

var name = "Worker";
self.addEventListener("message", (e)=>{
  if(typeof e.data.newName=="string") {
    name = e.data.newName;
  }
  if(e.data.command == "sendName") {
    self.postMessage({myName: name});
  }
});

Needless to say, if you send new name to the worker, the response to the "sendName" messages will be different from that point. Such change to behaviour is trivial, but can be arbitrarily complex.

---

If you're interested in actor model also see javascript implementation Vert.x.

Note: there are ways to block between Workers, but those are hacks and are not intended. One I can think of is asynchronous XHR with server holding the lock. I don't think this counts as exception of actor model.