302229 - Removing an observer inside NotifyObservers can be problematic

Status: RESOLVED WORKSFORME

(Core :: XPCOM, defect)

Description

[Darin Fisher]

Removing an observer inside NotifyObservers can be problematic.

It turns out that it is okay to remove an observer while it is being notified. 
This is because the observer service notifies observers in reverse order. 
However, it seems that there could be a problem if a different observer were
removed during a NotifyObservers call.  I don't have an examples where this
happens in the wild, but I could imagine that some xpcom-shutdown observer might
shutdown some other modules that call RemoveObserver when shutdown.  That might
lead to a crash.

I'm filing this bug as unconfirmed because I haven't verified it with an actual
testcase yet.  This bug report is just based on code inspection.

Comment 1

[Benjamin Smedberg]

We cache the observer list before enumerating, this is safe.