1818738 - Using the Nimbus `on` function for listening for updates doesn't always trigger on startup

Status: RESOLVED FIXED

(Firefox :: Nimbus Desktop Client, defect, P1)

Description

[Travis Long [:travis_]]

According to the comments in the code around the observer function for Nimbus, the callback should be invoked when the experiments are loaded from disk to cover the cases where Firefox is starting or if the callback is registered after the event.

In a recent experiment I had made use of this callback functionality and relied on it for startup, and it did seem to work in my testing, but once it was enabled for the Nightly experiment it seems that it doesn't always trigger the callback to be invoked on every startup.

This may be my misunderstanding of the intent of this functionality, but I had assumed that this would ensure that the callback was triggered at least once when it was being registered if the client was already enrolled in the experiment that was being registered for.

(Late edit) I was also using this on function pretty early on in BrowserGlue right after Glean was initialized, so I'm not sure if that comes into play for debugging this issue, but it seemed relevant.

Comment 1

[Travis Long [:travis_]]

Since this functionality has been available for a while, there is a chance that it has impacted experiments and rollouts of anyone that relied on it.

Comment 2

[Beth Rennie [:beth] (she/her)]

Attachment: Bug 1818738 - Make the feature update event API more ergonomic r?aminomancer

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/a76fb56dfd4c
Make the feature update event API more ergonomic r=aminomancer,settings-reviewers,search-reviewers,Gijs,daleharvey

Comment 4

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/a76fb56dfd4c