Fix async interrupt breaking bookkeeping in a Summary #66
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jml
reviewed
Jul 28, 2022
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Thanks so much!
I've been out of the loop on prometheus-haskell for a while, so if another more active contributor comes along to do the review, please trust them over me.
I've tried to use https://conventionalcomments.org/ in my comments. I hope they are helpful.
| @@ -79,7 +79,7 @@ summary info quantiles_ = Metric $ do | |||
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| instance Observer Summary where | |||
| -- | Adds a new observation to a summary metric. | |||
| observe s v = doIO $ withMVar (reqSketch s) (`ReqSketch.insert` v) | |||
| observe s v = doIO $ withMVarMasked (reqSketch s) (\rs -> rs `ReqSketch.insert` v) | |||
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Question: What's the motivation for adding the \rs -> rs bit?
No particular objections, just curious.
| @@ -79,7 +79,7 @@ summary info quantiles_ = Metric $ do | |||
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| instance Observer Summary where | |||
| -- | Adds a new observation to a summary metric. | |||
| observe s v = doIO $ withMVar (reqSketch s) (`ReqSketch.insert` v) | |||
| observe s v = doIO $ withMVarMasked (reqSketch s) (\rs -> rs `ReqSketch.insert` v) | |||
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Suggestion: Add a comment explaining why we are masking here. Something along the lines of your PR description would be great.
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+1 on adding a comment directly to the code.
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We ran into an alert where an internal invariant had been broken in the
ReqSketchlibrary. As best as we can tell, it was triggered by an async interrupt causing an internal counter and array length to become out of sync.