nsWebShellWindow destructor prevents nsXULWindow destructor from clearing pointers from tree owners

RESOLVED FIXED in mozilla17



7 years ago
7 years ago


(Reporter: neil, Assigned: justin.lebar+bug)



Firefox Tracking Flags

(Not tracked)



(2 attachments, 1 obsolete attachment)



7 years ago
For some reason, nsWebShellWindow's destructor clears out the nsIWidget member inherited from nsXULWindow, accidentally bypassing nsXULWindow's destruction code. Previously someone has always managed to invoke Destroy manually, however as of bug 777063 it's definitely possible to tickle the code so that nsWebShellWindow gets destroyed before Destroy gets invoked. This prevents nsXULWindow from clearing the pointers in the tree owners which are now stale and promptly crash if any of the tree owner's methods get called.

As it happens, Destroy has an identical copy of the code to clear that member.

Comment 1

7 years ago
I meant bug 775676 of course...
Depends on: 775676
No longer depends on: 777063

Comment 2

7 years ago
Created attachment 646761 [details] [diff] [review]
Proposed patch
Assignee: nobody → neil
Attachment #646761 - Flags: review?(roc)
Created attachment 646769 [details] [diff] [review]
Patch, v1
Attachment #646769 - Flags: review?(roc)
Attachment #646761 - Attachment is obsolete: true
Attachment #646761 - Flags: review?(roc)


7 years ago
Assignee: neil → justin.lebar+bug
Sorry, I backed this out on inbound because it looks like it introduced a perma-orange in make check on Windows debug builds:


mozilla::ShutdownXPCOM[xul +0x1253D82]
ScopedXPCOM::~ScopedXPCOM[TestAppShellSteadyState +0x37E0]
main[TestAppShellSteadyState +0x5970]
__tmainCRTStartup[TestAppShellSteadyState +0x97EF]
mainCRTStartup[TestAppShellSteadyState +0x961F]
BaseThreadInitThunk[kernel32 +0x133CA]
RtlInitializeExceptionChain[ntdll +0x39ED2]
RtlInitializeExceptionChain[ntdll +0x39EA5]

###!!! Deadlock may happen NOW!

###!!! ASSERTION: Potential deadlock detected:
Cyclical dependency starts at
Mutex : nsWindowMediator.mListLock (currently acquired)
Cycle completed at
Mutex : nsWindowMediator.mListLock (currently acquired)

Comment 6

7 years ago
Annoying. The test shuts down XPCOM while the window is still open, causing the window mediator to unregister all of its windows. Because it's the owner of last resort, this causes the destructor to run, which (with this patch) causes the nsXULWindow to try to unregister itself again.
Sounds like we should make sure we don't re-enter nsXULWindow::Destroy.

Comment 9

7 years ago
(In reply to Justin Lebar from comment #7)
> Sounds like we should make sure we don't re-enter nsXULWindow::Destroy.
We don't, this is the only call to nsXULWindow::Destroy in the test.
Created attachment 648005 [details] [diff] [review]
Part 1a, v1: Release the references after we release the lock.

As Neil pointed out on IRC, we don't actually need this additional block scope, so long as the array is declared before the auto-lock.  I think it clarifies things, but I'm not attached to it.
Attachment #648005 - Flags: review?(roc)
Comment on attachment 648005 [details] [diff] [review]
Part 1a, v1: Release the references after we release the lock.

Last Resolved: 7 years ago
Resolution: --- → FIXED
Target Milestone: --- → mozilla17
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