metrics: Add CaptureRuntimeMemStatsWithContext function (#124)

metrics/registry.go

@@ -5,6 +5,7 @@
 package metrics
 
 import (
+	"context"
 	"fmt"
 	"sort"
 	"strings"
@@ -81,6 +82,10 @@ type Registry interface {
 	Unregister(name string, tags ...Tag)
 }
 
+type metricsRegistryProvider interface {
+	Registry() metrics.Registry
+}
+
 // NewRootMetricsRegistry creates a new root registry for metrics. This call also starts a goroutine that captures Go
 // runtime information as metrics at the specified frequency.
 func NewRootMetricsRegistry() RootRegistry {
@@ -93,7 +98,15 @@ func NewRootMetricsRegistry() RootRegistry {
 var runtimeMemStats sync.Once
 
 // CaptureRuntimeMemStats registers runtime memory metrics collectors and spawns
-// a goroutine which collects them every collectionFreq.
+// a goroutine which collects them every collectionFreq. This function can only be called once per lifetime of the
+// process and only records metrics if the provided RootRegistry is a *rootRegistry.
+//
+// Deprecated: use CaptureRuntimeMemStatsWithCancel instead. CaptureRuntimeMemStatsWithCancel has the following
+// advantages over this function:
+//   * Does not make assumptions about the concrete struct implementing of RootRegistry
+//   * Does not restrict the function to being called only once globally
+//   * Supports cancellation using a provided context
+//   * Can tell if provided RootRegistry does not support Go runtime metric collection based on return value
 func CaptureRuntimeMemStats(registry RootRegistry, collectionFreq time.Duration) {
 	runtimeMemStats.Do(func() {
 		if reg, ok := registry.(*rootRegistry); ok {
@@ -104,6 +117,39 @@ func CaptureRuntimeMemStats(registry RootRegistry, collectionFreq time.Duration)
 	})
 }
 
+// CaptureRuntimeMemStatsWithContext creates a child registry of the provided registry that tracks Go runtime memory
+// metrics and starts a goroutine that captures them to that registry every collectionFreq. This function only supports
+// RootRegistry implementations that implement the metricsRegistryProvider interface -- if the provided RootRegistry
+// does not satisfy this interface, this function is a no-op. This function returns true if it starts the runtime metric
+// collection goroutine, false otherwise. If this function starts a goroutine, the goroutine runs until the provided
+// context is done.
+//
+// The gauges/metrics etc. used to track runtime statistics are shared globally and the values are reset every time this
+// function is called (if it is not a no-op). Note that this function should typically only be called once per Go
+// runtime, but no enforcement of this is performed.
+func CaptureRuntimeMemStatsWithContext(ctx context.Context, registry RootRegistry, collectionFreq time.Duration) bool {
+	mRegProvider, ok := registry.(metricsRegistryProvider)
+	if !ok {
+		return false
+	}
+
+	goRegistry := metrics.NewPrefixedChildRegistry(mRegProvider.Registry(), "go.")
+	metrics.RegisterRuntimeMemStats(goRegistry)
+	go func() {
+		ticker := time.NewTicker(collectionFreq)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				metrics.CaptureRuntimeMemStatsOnce(goRegistry)
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+	return true
+}
+
 type rootRegistry struct {
 	// the actual metrics.Registry on which all metrics are installed.
 	registry metrics.Registry
@@ -285,6 +331,10 @@ func (r *rootRegistry) HistogramWithSample(name string, sample metrics.Sample, t
 	return metrics.GetOrRegisterHistogram(r.registerMetric(name, tags), r.registry, sample)
 }
 
+func (r *rootRegistry) Registry() metrics.Registry {
+	return r.registry
+}
+
 func DefaultSample() metrics.Sample {
 	return metrics.NewExpDecaySample(defaultReservoirSize, defaultAlpha)
 }