Bug 67385 – Don't use MainThread in JSC

• Status: NEW
• Component: Web Template Framework

[Patrick R. Gansterer]

Don't use MainThread in JSC

[Patrick R. Gansterer]

Created attachment 105936 [details]
Patch

[Darin Adler]

Gavin, do you think this change is OK?

[Alexey Proskuryakov]

+        JSC has no concept of a MainThread.

This is incorrect. JavaScriptCore must be initialized from the main thread before use, see comments in JavaScriptCore/runtime/InitializeThreading.h.

What seems wrong here is that WTF exposes a separate initializeMainThread() function in addition to initializeThreading(), which also must be called from main thread.

[Patrick R. Gansterer]

(In reply to comment #3)
> +        JSC has no concept of a MainThread.
> 
> This is incorrect. JavaScriptCore must be initialized from the main thread before use, see comments in JavaScriptCore/runtime/InitializeThreading.h.
Sure?
AFAIK it is possible to run (and init) JSC from any thead when embedded into an other application. That's not necessary the MainThread.
The only use of the MainThread is the assertion in the patch.

[Alexey Proskuryakov]

There is certainly a comment in the header saying that it is a requirement, yes. Whether we should strive to lift that restriction is a separate question, and there are of course many things that could be improved regardless (like the mysterious separate initializeMainThread () call mentioned above).

However, it won't be easy to move MainThread functionality from WTF to WebCore, because this will break nightly builds (Safari uses this functionality through WTF).

[Patrick R. Gansterer]

(In reply to comment #5)
> However, it won't be easy to move MainThread functionality from WTF to WebCore, because this will break nightly builds (Safari uses this functionality through WTF).
Do you see any chance/way to move it to WebCore? On Linux the MainThread functionality isn't provided by the OS and needs an higher level library like Gtk/Qt/wx for this.

[David Levin]

(In reply to comment #3)
> +        JSC has no concept of a MainThread.
> 
> This is incorrect. JavaScriptCore must be initialized from the main thread before use, see comments in JavaScriptCore/runtime/InitializeThreading.h.
> 
"This function must be called from the main thread. ... Darwin is an exception to this rule" -- http://trac.webkit.org/browser/trunk/Source/JavaScriptCore/runtime/InitializeThreading.h

I think this is because JavaScriptCore may be run from any thread. (I hit this issue before that the JavaScript API doesn't require is main thread to be set.)

However, I don't think this bug/patch has made the case for why MainThread shouldn't be used anywhere in WTF or why it should be moved out of WTF (but I'll admit that it is a tricky area that I messed up before -- I used isMainThread in a place where I shouldn't have).

[Eric Seidel (no email)]

Comment on attachment 105936 [details]
Patch

My understanding is that you *must* initialize JSC (and all our various hashes) on the main thread.  This patch looks wrong.