1644714 - Got a mutation for an unexpected actor: server0.conn0.child2/domnode37

Status: NEW

(DevTools :: Inspector, defect, P3)

Description

[Frederik Braun [:freddy]]

Thank you for helping make Firefox better. If you are reporting a defect, please complete the following:

What were you doing?

1. went to example.com
2. opened devtools style editor, added a new sheet (plus icon)
3. made that sheet contain a style of "body{background-color:black}"
4. went to debugger panel
5. navigated the top page to srihash.org

What happened?

I observed the warning "Got a mutation for an unexpected actor". Being a good citizen, I am reporting it here. Not sure how and if that's helping you :-)

console.trace: 
resource://devtools/client/fronts/walker.js 284 getMutations
resource://devtools/client/fronts/walker.js 418 onMutations
resource://devtools/shared/protocol/Front.js 283 onPacket
resource://devtools/client/devtools-client.js 493 onPacket
resource://devtools/shared/transport/local-transport.js 68 send/<
resource://devtools/shared/ThreadSafeDevToolsUtils.js 103 exports.makeInfallible/<
resource://devtools/shared/ThreadSafeDevToolsUtils.js 103 exports.makeInfallible/<

What should have happened?

No mutation.

Anything else we should know?

This is on a custom-build nightly, but no different behavior patched in. Just a bit of random logging. Revision id is b2df79a80c0303df9d710800ae37dce56847eef5(hg) and 40ac01e9607e505c64ca0534cca212c874de6700 (git

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:Honza, could you have a look please?

For more information, please visit auto_nag documentation.

Comment 2

[Jan Honza Odvarko [:Honza] (always need-info? me)]

Julian, can please look at this?

Honza

Comment 3

[Julian Descottes [:jdescottes]]

(Moving it to inspector for triage.)

I can't reproduce the issue with the provided STRs, but it's not that surprising.

For the record we have several other bugs similar to this:
https://bugzilla.mozilla.org/buglist.cgi?quicksearch=mutation%20actor&list_id=15309219

The inspector walker actor maintains the list of known nodes on the server, in order to know which mutations need to be sent to the client.
But this code can be racy / buggy. Mutations are queued so it's pretty easy to queue a mutation for a node which will be destroyed in the meantime.

Honestly I think calling for bug filing in the warning message is too much, as most of the time we can't consistently reproduce the issues:

console.warn(
  "Got a mutation for an unexpected actor: " +
    targetID +
    ", please file a bug on bugzilla.mozilla.org!"
);

https://searchfox.org/mozilla-central/rev/a87a1c3b543475276e6d57a7a80cb02f3e42b6ed/devtools/client/fronts/walker.js#282

I suggest repurposing the bug in order to modify the error message, considering that those bugs are not actionable 99% of the time.

Comment 4

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:gl, could you have a look please?

For more information, please visit auto_nag documentation.