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This change enables setting min and max values for gauges. It prevent… #1872

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This change enables setting min and max values for gauges. It prevent… #1872

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47 changes: 43 additions & 4 deletions prometheus/gauge.go
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Original file line number Diff line number Diff line change
Expand Up @@ -52,8 +52,37 @@ type Gauge interface {
SetToCurrentTime()
}

// GaugeOpts is an alias for Opts. See there for doc comments.
type GaugeOpts Opts
type GaugeOpts struct {
// Namespace, Subsystem, and Name are components of the fully-qualified
// name of the Metric (created by joining these components with
// "_"). Only Name is mandatory, the others merely help structuring the
// name. Note that the fully-qualified name of the metric must be a
// valid Prometheus metric name.
Namespace string
Subsystem string
Name string

// Help provides information about this metric.
//
// Metrics with the same fully-qualified name must have the same Help
// string.
Help string

// ConstLabels are used to attach fixed labels to this metric. Metrics
// with the same fully-qualified name must have the same label names in
// their ConstLabels.
//
// ConstLabels are only used rarely. In particular, do not use them to
// attach the same labels to all your metrics. Those use cases are
// better covered by target labels set by the scraping Prometheus
// server, or by one specific metric (e.g. a build_info or a
// machine_role metric). See also
// https://prometheus.io/docs/instrumenting/writing_exporters/#target-labels-not-static-scraped-labels
ConstLabels Labels

MinValue *float64
MaxValue *float64
}

// GaugeVecOpts bundles the options to create a GaugeVec metric.
// It is mandatory to set GaugeOpts, see there for mandatory fields. VariableLabels
Expand Down Expand Up @@ -82,7 +111,7 @@ func NewGauge(opts GaugeOpts) Gauge {
nil,
opts.ConstLabels,
)
result := &gauge{desc: desc, labelPairs: desc.constLabelPairs}
result := &gauge{desc: desc, labelPairs: desc.constLabelPairs, minValue: opts.MinValue, maxValue: opts.MaxValue}
result.init(result) // Init self-collection.
return result
}
Expand All @@ -97,6 +126,8 @@ type gauge struct {

desc *Desc
labelPairs []*dto.LabelPair
minValue *float64
maxValue *float64
}

func (g *gauge) Desc() *Desc {
Expand All @@ -122,7 +153,15 @@ func (g *gauge) Dec() {
func (g *gauge) Add(val float64) {
for {
oldBits := atomic.LoadUint64(&g.valBits)
newBits := math.Float64bits(math.Float64frombits(oldBits) + val)
oldVal := math.Float64frombits(oldBits)
newVal := oldVal + val
if g.minValue != nil && newVal < *g.minValue {
newVal = *g.minValue
} else if g.maxValue != nil && newVal > *g.maxValue {
newVal = *g.maxValue
}

newBits := math.Float64bits(newVal)
if atomic.CompareAndSwapUint64(&g.valBits, oldBits, newBits) {
return
}
Expand Down
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