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We should update and start the ticker metrics before we return from an error. #64

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merged 3 commits into from
Oct 15, 2021
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We should update and start the ticker metrics before we return from an error. #64

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c589321
We should update and start the ticker metrics before we return. This …
Oct 14, 2021
23af6d8
Move metrics update and ticker start to after an error could be retur…
Oct 14, 2021
ba77a90
Refactor ordering of metrics update and nil check for value
Oct 15, 2021
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9 changes: 5 additions & 4 deletions ring/ring.go
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Original file line number Diff line number Diff line change
Expand Up @@ -276,14 +276,14 @@ func (r *Ring) starting(ctx context.Context) error {
if err != nil {
return errors.Wrap(err, "unable to initialise ring state")
}
if value == nil {
if value != nil {
r.updateRingState(value.(*Desc))
} else {
level.Info(r.logger).Log("msg", "ring doesn't exist in KV store yet")
return nil
}

r.updateRingState(value.(*Desc))
// Update the ring metrics at start.
r.updateRingMetrics()
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I'm going to approve it to unblock you, but my point (that I tried to mention offline on Slack) is that given we haven't called updateRingState() yet at this point, I see useless calling updateRingMetrics() here. Why do we need it? Shouldn't we call updateRingMetrics() after updateRingState() below in the function?

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I changed the ordering in this PR to reflect this. Yeah, I see what you mean, we should attempt to update the ring state before updating the ring metrics for the case where we do actually get something back from the kv store. I'm going to merge this PR to unblock myself and do a refactor to move this to loop which will also solve this problem.


// Use this channel to close the go routine to prevent leaks.
r.metricsUpdateCloser = make(chan struct{})
go func() {
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If I remember correctly the service framework, if starting returns an error, the stopping won't be called. Could you double check it? If confirmed, then we should start the ticker at last, otherwise we'll leak the goroutine.

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It doesn't look like we do, I'll fix that here, but it that something we should make a issue for in basic services?

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this is already starting goroutine as last thing in starting, it looks good to me.

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@pstibrany pstibrany Oct 15, 2021 •
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We can also start it in loop, and make metricsUpdateCloser scoped to loop only. That would actually solve the original problem in this method as well (early return when value was nil).

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I took a look at some services in cortex proper and using the loop function for starting the ticker and using the context to exit is our common pattern. I'm going to move to that pattern for this ticker here as well.

Expand All @@ -300,6 +300,7 @@ func (r *Ring) starting(ctx context.Context) error {
}
}
}()

return nil
}

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