Struct histogram

prometheus/histogram.go:708–760

}

type histogram struct {
	// countAndHotIdx enables lock-free writes with use of atomic updates.
	// The most significant bit is the hot index [0 or 1] of the count field
	// below. Observe calls update the hot one. All remaining bits count the
	// number of Observe calls. Observe starts by incrementing this counter,
	// and finish by incrementing the count field in the respective
	// histogramCounts, as a marker for completion.
	//
	// Calls of the Write method (which are non-mutating reads from the
	// perspective of the histogram) swap the hot–cold under the writeMtx
	// lock. A cooldown is awaited (while locked) by comparing the number of
	// observations with the initiation count. Once they match, then the
	// last observation on the now cool one has completed. All cold fields must
	// be merged into the new hot before releasing writeMtx.
	//
	// Fields with atomic access first! See alignment constraint:
	// http://golang.org/pkg/sync/atomic/#pkg-note-BUG
	countAndHotIdx uint64

	selfCollector
	desc *Desc

	// Only used in the Write method and for sparse bucket management.
	mtx sync.Mutex

	// Two counts, one is "hot" for lock-free observations, the other is
	// "cold" for writing out a dto.Metric. It has to be an array of
	// pointers to guarantee 64bit alignment of the histogramCounts, see
	// http://golang.org/pkg/sync/atomic/#pkg-note-BUG.
	counts [2]*histogramCounts

	upperBounds                     []float64
	labelPairs                      []*dto.LabelPair
	exemplars                       []atomic.Value // One more than buckets (to include +Inf), each a *dto.Exemplar.
	nativeHistogramSchema           int32          // The initial schema. Set to math.MinInt32 if no sparse buckets are used.
	nativeHistogramZeroThreshold    float64        // The initial zero threshold.
	nativeHistogramMaxZeroThreshold float64
	nativeHistogramMaxBuckets       uint32
	nativeHistogramMinResetDuration time.Duration
	// lastResetTime is protected by mtx. It is also used as created timestamp.
	lastResetTime time.Time
	// resetScheduled is protected by mtx. It is true if a reset is
	// scheduled for a later time (when nativeHistogramMinResetDuration has
	// passed).
	resetScheduled  bool
	nativeExemplars nativeExemplars

	// now is for testing purposes, by default it's time.Now.
	now func() time.Time

	// afterFunc is for testing purposes, by default it's time.AfterFunc.
	afterFunc func(time.Duration, func()) *time.Timer
}

func (h *histogram) Desc() *Desc {
	return h.desc