742371 - Remove MutationReceiver from MutationObserver when the target is deleted

Status: RESOLVED FIXED

(Core :: DOM: Core & HTML, defect)

Description

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

Attachment: patch

Currently if target is deleted, MutationObserver ends up having receivers
with null target. Nothing scary there, but no need to keep such things
alive.

This patch fixes also transient receiver disconnecting.
s/Disconnect/DisconnectTransientReceiver/

The patch adds also some warnings and assertions.

Comment 1

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

Comment on attachment 612183 [details] [diff] [review]
patch

If I understand correctly NodeWillBeDestroyed can only be called on non-transient receivers, since transient receivers are always attached to nodes which we hold a strong reference to in a MutationRecord.

Is this correct?

If so, could you add an assertion to NodeWillBeDestroyed that checks that the receiver doesn't have a parent? Mostly as documentation, but also to make sure that we don't have any bad bugs.

Comment 2

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

(In reply to Jonas Sicking (:sicking) from comment #1)
> Comment on attachment 612183 [details] [diff] [review]
> patch
> 
> If I understand correctly NodeWillBeDestroyed can only be called on
> non-transient receivers, since transient receivers are always attached to
> nodes which we hold a strong reference to in a MutationRecord.
> 
> Is this correct?
No, but nsMutationObserver has node->transientobserverlist hashtable.
That keeps node and transientobservers alive.


> 
> If so, could you add an assertion to NodeWillBeDestroyed that checks that
> the receiver doesn't have a parent? Mostly as documentation, but also to
> make sure that we don't have any bad bugs.
Sure.

Comment 3

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

Attachment: +assertion

Comment 4

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

https://hg.mozilla.org/mozilla-central/rev/320065be1731

Comment 5

[Jonas Sicking (:sicking) No longer reading bugmail consistently]

Makes sense.