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Fix race condition with Exemplar in Counter #1146

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Merged
merged 2 commits into from
Oct 17, 2022
Merged

Fix race condition with Exemplar in Counter #1146

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9e13cd2
Fix race condition with Exemplar in Counter
fstab Oct 7, 2022
037699f
Fix race condition with Exemplar in Counter
fstab Oct 17, 2022
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5 changes: 3 additions & 2 deletions prometheus/counter.go
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Original file line number Diff line number Diff line change
Expand Up @@ -140,12 +140,13 @@ func (c *counter) get() float64 {
}

func (c *counter) Write(out *dto.Metric) error {
val := c.get()

// Read the Exemplar first and the value second. This is to avoid a race condition
// where users see an exemplar for a not-yet-existing observation.
var exemplar *dto.Exemplar
if e := c.exemplar.Load(); e != nil {
exemplar = e.(*dto.Exemplar)
}
val := c.get()

return populateMetric(CounterValue, val, c.labelPairs, exemplar, out)
}
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