522245 - It should be possible to initiate cycle collection without nsIDOMWindowUtils

Status: RESOLVED FIXED

(Core :: XPConnect, defect)

Description

[Atul Varma [:atul]]

In Jetpack's test suite, we use Components.utils.forceGC() in concert with Components.utils.getWeakReference() to "track" objects of interest and ensure that unit/functional tests don't have memory leaks (this is intended to help find memory leaks in the underlying implementation).

We found, though, that when making weak references to DOM objects like iframes, Cu.forceGC() didn't get rid of them--but that the iframe would eventually disappear.

I realized a few days ago while learning about the cycle collector that this is due to the fact that Cu.forceGC() is a simple wrapper for the JSAPI's JS_GC(), which itself doesn't result in cycle collection.  In order for cycle collection to occur, nsCycleCollector_collect() needs to be called.

I can see two ways of enabling this:

  (1) Modify Cu.forceGC() to call nsCycleCollector_collect() instead of JS_GC(). There's no need to additionally call JS_GC() because performing cycle collection also performs standard mark-and-sweep GC'ing.

  (2) Add a new Cu.forceCC() or Cu.forceCycleCollection() function that calls nsCycleCollector_collect().

I'd be happy to provide a patch for either. Just let me know which is preferred, or if you have a better solution in mind.

Comment 1

[Olli Pettay [:smaug][[e-mail]]]

http://mxr.mozilla.org/mozilla-central/source/dom/interfaces/base/nsIDOMWindowUtils.idl#250

Comment 2

[Ben Turner (not reading bugmail, use the needinfo flag!)]

As Olli points out, you can do a cycle collection via a window's nsIDOMWindowUtils, so that should work for JetPack.

Other folks need this from xpcshell or from a JS component, however, where windows are not available. Let's morph this bug to cover those cases.

Comment 3

[Alex Vincent [:WeirdAl]]

Related to bug 465809?

Comment 4

[BMO Automation]

Per policy at https://wiki.mozilla.org/Bug_Triage/Projects/Bug_Handling/Bug_Husbandry#Inactive_Bugs. If this bug is not an enhancement request or a bug not present in a supported release of Firefox, then it may be reopened.

Comment 5

[Boris Zbarsky [:bzbarsky]]

Fixed in bug 781700: Cu.forceCC() works.