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Fix race condition with Exemplar in Counter (#1146) 

* Fix race condition with Exemplar in Counter

Potential fix for #1145.

Signed-off-by: Fabian Stäber <fabian@fstab.de>

* Fix race condition with Exemplar in Counter

Signed-off-by: Fabian Stäber <fabian@fstab.de>

Signed-off-by: Fabian Stäber <fabian@fstab.de>
This commit is contained in:
Fabian Stäber 2022-10-17 20:50:50 +02:00 committed by GitHub
parent dcea97eee2
commit 10b0550932
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1 changed files with 3 additions and 2 deletions
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5
prometheus/counter.go
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@ -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)
}