1561061 - Move (push|pop|flush)PrefEnv logic into the parent process

Status: RESOLVED FIXED

(Testing :: Mochitest, task, P2)

Description

[Kris Maglione [:kmag]]

Bug 1541557 fixes most of the pref env issues related to OOP frames, but there are still a few remaining. In particular:

1. There is some test harness code that expects flushPrefEnv to flush any preference environments, no matter which SpecialPowers instance they were created in. The works at the moment (mostly, and mostly by accident) for any SpecialPowers instances in the same process as the instance that flush is called in, but not for instances in remote processes.

2. The pushPrefEnv code reads the current value of the preference in the child process to determine which value to restore. Unfortunately, there are some preferences whose changed values are never propagated to content processes, only their original values, which may lead to strange issues when used with this API. This is to say nothing of races.

3. In some cases, when one of the issues in #2 arises, we may not get a preference observer notification for one of the preference changes, in which case the API will continue waiting forever for its changes to take effect, and will not resolve its returned promises, leading to hard-to-diagnose test timeouts.

4. This code is all horrendously complex, and difficult to maintain.

And, while not strictly related to fission, there's also,

5. As reported in bug 1557397, when the API believes that all of the preferences it is asked to change have their required values, it returns immediately, without pushing anything onto the undo stack, leading the next popPrefEnv call to pop the wrong environment off of the stack, causing any number of arcane bugs to popup.

Comment 1

[Kris Maglione [:kmag]]

Attachment: Bug 1561061: Move SpecialPowers pref env code to parent and make sane-ish. r=aswan

Comment 2

[Kris Maglione [:kmag]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/c2d0956f41d82e76c682f829807e818863cd802a
Bug 1561061: Move SpecialPowers pref env code to parent and make sane-ish. r=aswan

Comment 3

[Kris Maglione [:kmag]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/fa5e186e16357ff48a58b2035e4432f8688b00fc
Bug 1561061: Follow-up: Fix race in gamepad tests. r=bustage CLOSED TREE

Comment 4

[Kris Maglione [:kmag]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/6fc41e51bcee6e1854bcacbf7356f30a9f47463b
Bug 1561061: Follow-up: Fix another test race in pushPrefEnv. r=bustage CLOSED TREE

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/72cd895b1613
Move SpecialPowers pref env code to parent and make sane-ish. r=aswan

Comment 6

[Razvan Maries]

https://hg.mozilla.org/mozilla-central/rev/72cd895b1613

Comment 7

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

Backed out 34 changesets (bug 1561150, bug 1541557, bug 1561724, bug 1561999, bug 1558298, bug 1561061, bug 1532795, bug 1560400, bug 1561122) for beta simulation failures (bug 1563905, bug 1564001):
https://hg.mozilla.org/mozilla-central/rev/7e6657f88b7694ecd841088963ff71d767e4ec22

Comment 8

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

Relanded (backout got backed out):
https://hg.mozilla.org/mozilla-central/rev/e596664275d5e3e2fdcb7fa8d1447289f99269c3