617251 - Can't send strings to threads

Status: RESOLVED INVALID

(Core :: JavaScript Engine, defect)

Description

[Erik Vold]

My extension Scriptish https://addons.mozilla.org/en-US/firefox/addon/231203/ implements Workers using threads which pass strings between threads, which no longer works because of bug 608142 which offers no alternative method to implement this.

Comment 1

[Boris Zbarsky [:bzbarsky]]

We should be able to make this work for strings specifically by copying the string, I'd think.  Performance would possibly suck, but...

Comment 2

[Andreas Gal :gal]

Yeah, we can definitely allow strings through here. Erik, does that fix your use case?

Comment 3

[Erik Vold]

(In reply to comment #2)
> Yeah, we can definitely allow strings through here. Erik, does that fix your
> use case?

Yes that should be all that I need.

Comment 4

[Andreas Gal :gal]

Just to be clear though, you can't send closures across. How do you execute code on a thread right now without workers?

Comment 5

[Erik Vold]

(In reply to comment #4)
> Just to be clear though, you can't send closures across. How do you execute
> code on a thread right now without workers?

https://github.com/erikvold/scriptish/blob/master/extension/modules/api/GM_worker.js#L156

I took a closer look at my implementation and have been thinking about this all night, and I am sharing objects atm.

At first I thought I could just pass messages + signatures to a singleton dispatcher, instead of making dynamic dispatchers as I am now, but now I'm wondering how to pass the string from the background thread to the dispatcher in the main thread, and atm I can't think of a way to do that..

Comment 6

[Nils Maier [:nmaier]]

(In reply to comment #5)
> ... but now I'm
> wondering how to pass the string from the background thread to the dispatcher
> in the main thread ...

That's not the actual problem here: While you can still create a background thread using newThread() you cannot (from js) dispatch any runnable code to this new thread. So in fact, you don't have a background thread (here: javascript implementation of nsIRunnable running on a background thread) that needs to dispatch anything back to the main thread ;)

In your code fake_worker.run is in fact never called as you're trying to execute instances of it on a |newThread(0)|. And that's exactly what bug 608142 doesn't permit any longer. Your |dispatch(this, ...)| fails silently[1].

The nsIThreadManager API is dead when it comes to creating new threads to execute js-implemented nsIRunnables.
There aren't any full-featured alternatives: Neither Workers nor JetPack processes allow XPCOM access.

[1]
https://github.com/erikvold/scriptish/blob/master/extension/modules/api/GM_worker.js#L74
Assuming this.thread points to a new thread, like it does right now.

Comment 7

[Erik Vold]

(In reply to comment #6)
> (In reply to comment #5)
> > ... but now I'm
> > wondering how to pass the string from the background thread to the dispatcher
> > in the main thread ...
> 
> That's not the actual problem here: While you can still create a background
> thread using newThread() you cannot (from js) dispatch any runnable code to
> this new thread.

So what can you do with a thread then?

> So in fact, you don't have a background thread that
> needs to dispatch anything back to the main thread ;)

huh?