1148504 - Protect Firefox Account state with a critical section

Status: RESOLVED FIXED

(Android Background Services Graveyard :: Reading List Sync, defect)

Description

[Nick Alexander :nalexander [he/him]]

We now have two (background) Firefox Account consumers, Sync and RL.  Due to time pressure, we haven't implemented a nice API for them both to update the account state; instead, they both try to own the state, resulting in races.  The effect is most noticeable when an account is created or re-connected: it's frequent that both consumers will try to fetch keys using the same keyFetchToken; one will win the race and proceed to start syncing; the other will fail to fetch keys and drive the account to Separated (in order to fetch keys).  Result: a terrible user experience.

As a step towards a better API, we need to protect the Account state with a critical section.  Eventually, we transition Sync to requesting token server tokens from the FxAccountAuthenticator using Android's APIs, which makes this much cleaner (since there's then a single consumer to handle locking).

Comment 1

[Nick Alexander :nalexander [he/him]]

Attachment: Link to Github pull-request: https://github.com/mozilla-services/android-sync/pull/543

rnewman: how do you feel about this?  It's working well locally.

I intended to include telemetry for how long we wait and how long we hold the lock, but I then observed (and explained in the second commit comment) that we should very rarely wait.

Comment 2

[Nick Alexander :nalexander [he/him]]

https://hg.mozilla.org/integration/fx-team/rev/c4639723e721

Comment 3

[Ryan VanderMeulen [:RyanVM]]

Backed out for bustage.
https://hg.mozilla.org/integration/fx-team/rev/cb309087f978

https://treeherder.mozilla.org/logviewer.html#?job_id=2452077&repo=fx-team

Comment 4

[Richard Newman [:rnewman]]

https://hg.mozilla.org/integration/fx-team/rev/2c562029850b

Comment 5

[Nick Alexander :nalexander [he/him]]

https://hg.mozilla.org/mozilla-central/rev/2c562029850b

Comment 6

[Richard Newman [:rnewman]]

https://hg.mozilla.org/releases/mozilla-beta/rev/32b6b2c4a69e