784360 - java.util.ConcurrentModificationException: at java.util.HashMap$HashIterator.nextEntry(HashMap.java) at org.mozilla.gecko.DoorHangerPopup.onTabChanged(DoorHangerPopup.java)

Status: VERIFIED FIXED

(Firefox for Android Graveyard :: General, defect)

Description

[Scoobidiver (away)]

It first appeared in 17.0a1/20120806. The regression range is likely:
http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=9453cf029b72&tochange=c8d94fe7506a
It's likely a regression from bug 732336.

Here is a crash report: bp-28152574-c339-4b59-8b99-62f822120821.

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextEntry(HashMap.java:796)
	at java.util.HashMap$KeyIterator.next(HashMap.java:823)
	at org.mozilla.gecko.DoorHangerPopup.onTabChanged(DoorHangerPopup.java:99)
	at org.mozilla.gecko.Tabs.notifyListeners(Tabs.java:369)
	at org.mozilla.gecko.Tabs.notifyListeners(Tabs.java:358)
	at org.mozilla.gecko.Tabs$3.run(Tabs.java:183)
	at android.os.Handler.handleCallback(Handler.java:587)
	at android.os.Handler.dispatchMessage(Handler.java:92)
	at android.os.Looper.loop(Looper.java:143)
	at android.app.ActivityThread.main(ActivityThread.java:4196)
	at java.lang.reflect.Method.invokeNative(Native Method)
	at java.lang.reflect.Method.invoke(Method.java:507)
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
	at dalvik.system.NativeStart.main(Native Method)

More reports at:
https://crash-stats.mozilla.com/report/list?signature=java.util.ConcurrentModificationException%3A+at+java.util.HashMap%24HashIterator.nextEntry%28HashMap.java%29

Comment 1

[:Margaret Leibovic]

Attachment: patch

Sigh, threads. I'm not sure if this is the smartest way to avoid a ConcurrentModificationException, but it's what we've done elsewhere. There are also things like CopyOnWriteArrayList, but that feels too heavyweight for this case.

Comment 2

[Wesley Johnston (:wesj)]

Comment on attachment 656673 [details] [diff] [review]
patch

Review of attachment 656673 [details] [diff] [review]:
-----------------------------------------------------------------

I think it'd be cleaner to just use synchronized here. We aren't going to be doing so much with this list that I expect that to happen often. It matches well with the advice from here:

http://developer.android.com/reference/java/util/concurrent/package-summary.html

"A CopyOnWriteArrayList is preferable to a synchronized ArrayList when the expected number of reads and traversals greatly outnumber the number of updates to a list."

Comment 3

[:Margaret Leibovic]

(In reply to Wesley Johnston (:wesj) from comment #2)

> I think it'd be cleaner to just use synchronized here.

Where would we use synchronized? I see above that I mentioned threads, but thinking about it more, the problem isn't that this is being accessed from multiple threads, the problem is that we're modifying the array as we're iterating over it. I've found I can reliably reproduce this crash if I close any tab that has multiple doorhangers (a good testcase is http://people.mozilla.com/~mwargers/tests/dom/multiple_doorhangers.htm).

Comment 4

[:Margaret Leibovic]

Wes, poke. See comment 3.

Comment 5

[Scoobidiver (away)]

It's #8 top crasher in 17.0b1.

Comment 6

[:Margaret Leibovic]

Comment on attachment 656673 [details] [diff] [review]
patch

Wes, can you re-review this? See comment 3.

Comment 7

[Wesley Johnston (:wesj)]

Comment on attachment 656673 [details] [diff] [review]
patch

Review of attachment 656673 [details] [diff] [review]:
-----------------------------------------------------------------

Ok. I can live with this.

Comment 8

[:Margaret Leibovic]

https://hg.mozilla.org/integration/mozilla-inbound/rev/8595e313fc21

Comment 9

[:Margaret Leibovic]

Comment on attachment 656673 [details] [diff] [review]
patch

[Approval Request Comment]
Bug caused by (feature/regressing bug #): crash caused by bug 732336
User impact if declined: crash if you close a tab with multiple doorhanger notification messages
Testing completed (on m-c, etc.): just landed on inbound
Risk to taking this patch (and alternatives if risky): low-risk small self-contained change
String or UUID changes made by this patch: n/a

Comment 10

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/8595e313fc21

Comment 11

[:Margaret Leibovic]

https://hg.mozilla.org/releases/mozilla-aurora/rev/96a2697cec57
https://hg.mozilla.org/releases/mozilla-beta/rev/3a43c980820e

Comment 12

[Kevin Brosnan [Ex-Mozilla]]

This is still crashing on Firefox 17.

Comment 13

[:Margaret Leibovic]

(In reply to Kevin Brosnan [:kbrosnan] from comment #12)
> This is still crashing on Firefox 17.

The stacks for the recent crashes look different. I looked at the most recent 10, and they don't mention DoorHangerPopup at all. Please file a new bug.

Comment 14

[Kevin Brosnan [Ex-Mozilla]]

Verified then. I don't see any popup hanger crashes either.