740524 - identify zombie compartments automatically

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[Chris Pickett]

This is a request to identify zombie compartments automatically, which can then be used in other ways.

Comment 10 in Bug 695348 (ZombieHunter) suggests a mechanism for doing this:

(Justin Lebar [:jlebar] from https://bugzilla.mozilla.org/show_bug.cgi?id=695348#c10)
> > 4) If no -> all OK, if yes -> the test is creating a zombie compartment.
> 
> So you just want to know *if* there's a zombie, not *why*?  That's much
> easier.  You can do that right now by doing what about:memory does: Force a
> GC/CC, then read the compartment memory reporters.
> 
> See
> 
> http://hg.mozilla.org/mozilla-central/file/bcc015450e7a/toolkit/components/
> aboutmemory/content/aboutMemory.js#l176
> 
> http://hg.mozilla.org/mozilla-central/file/bcc015450e7a/toolkit/components/
> aboutmemory/content/aboutMemory.js#l243
> 
> There's no easy way at the moment to get just the compartment memory
> reporters, but if you read all the multi-reporters, you should be able to
> pick out the compartment ones easily.
 
The original suggestion was motivated by a desire to improve Firebug, see:

https://bugzilla.mozilla.org/show_bug.cgi?id=695348#c9

I was thinking you might also be able to do some tricks like freeing zombie compartments unsafely and trapping any accesses somehow, perhaps with a signal handler or by forcing checks for compartment liveness.

I'm filing a dependent bug after this one ("display zombie compartments in about:memory") that I think is a good motivator for the work.

Comment 1

[Nicholas Nethercote [inactive]]

We have ghost windows now (in about:compartments) -- see http://jlebar.com/2012/5/30/A_ghost_story.html for details.  Also, bug 695480 fixed almost all the zombie compartments caused by add-ons.  Do we still need this bug?

Comment 2

[Justin Lebar (not reading bugmail)]

No, I don't think so.