Prometheus client_golang histogram race

main.go

package main

import (
	"fmt"

	"github.com/golang/protobuf/proto"
	"github.com/prometheus/client_golang/prometheus"
	dto "github.com/prometheus/client_model/go"
)

func main() {
	hist := prometheus.NewHistogram(prometheus.HistogramOpts{
		Name:    "race",
		Help:    "racy racer",
		Buckets: []float64{1.0, 2.0},
	})

	go func() {
		for {
			hist.Observe(1.9)
		}
	}()

	res := make(chan *dto.Metric, 10000)
	go func() {
		for {
			var obs dto.Metric
			hist.Write(&obs)
			res <- &obs
		}
	}()

	i := 0
	for obs := range res {
		last := obs.Histogram.Bucket[len(obs.Histogram.Bucket)-1]
		if *obs.Histogram.SampleCount < *last.CumulativeCount {
			fmt.Println("found race")
			fmt.Println(proto.MarshalTextString(obs.Histogram))
			return
		}

		i++
		if i == 100000 {
			fmt.Print(".")
			i = 0
		}
	}
}