888736 - Metro Session Store throws in onTabClose during mochiperf/browser_msgmgr_01.js teardown

Status: RESOLVED INCOMPLETE

(Firefox for Metro Graveyard :: Components, defect)

Description

[Bobby Holley (:bholley)]

When trying to land bug 865745 (a major platform refactoring involving JSContexts), I ran into a failure in mochitest-metro-chrome (see bug 865745 comment 29).

The failure comes when we try to access aBrowser.__SS_extdata during teardown, which is undefined:
http://mxr.mozilla.org/mozilla-central/source/browser/metro/components/SessionStore.js#374

I hypothesized that we'd always thrown here, and that the platform changes just cause us to report the exception to onerror where we previously squelched it. To confirm my theory, I pushed a diagnostic patch to add  a try/catch block and dump() whether we throw in in onTabClose. I pushed one with the JSContext changes, and one without:

https://tbpl.mozilla.org/?tree=Try&rev=d0d7d9cabe88
https://tbpl.mozilla.org/?tree=Try&rev=97f6732f7f45

In both cases, the log shows the following:

INFO -  TEST-INFO | chrome://mochitests/content/metro/browser/metro/base/tests/mochiperf/browser_msgmgr_01.js | END msg manager 3
INFO -  Threw retrieving extData
INFO -  Threw retrieving extData
INFO -  Didn't throw retrieving extData
INFO -  INFO TEST-END | chrome://mochitests/content/metro/browser/metro/base/tests/mochiperf/browser_msgmgr_01.js | finished in 7852ms

This confirms my theory. And since we've always thrown here, we don't need to block bug 865745 on sorting this out. I'm pushing bug 865745 along with a patch to squelch the exception (which effectively mimics the old behavior). This allows the metro team to dig into this on their own time (if they want to at all).

Comment 1

[Jim Mathies [:jimm]]

Why is __SS_extdata undefined?

Comment 2

[Jim Mathies [:jimm]]

(In reply to Jim Mathies [:jimm] from comment #1)
> Why is __SS_extdata undefined?

Nm that. I see this is in our session restore code. We haven't done much work with this. I imagine it's a timing issue since this test runs for a very short period of time.

Comment 3

[Firefox Bug Husbandry Bot]

Mass close of bugs in obsolete product https://bugzilla.mozilla.org/show_bug.cgi?id=1350354