Add metrics registry package (#111)

metrics/context.go

@@ -0,0 +1,57 @@
+// Copyright (c) 2018 Palantir Technologies. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package metrics
+
+import (
+	"context"
+)
+
+type mContextKey string
+
+const (
+	registryKey = mContextKey("metrics-registry")
+	tagsKey     = mContextKey("metrics-tags")
+)
+
+var DefaultMetricsRegistry = NewRootMetricsRegistry()
+
+func WithRegistry(ctx context.Context, registry Registry) context.Context {
+	return context.WithValue(ctx, registryKey, registry)
+}
+
+func FromContext(ctx context.Context) Registry {
+	if registry, ok := ctx.Value(registryKey).(Registry); ok {
+		return registry
+	}
+	return DefaultMetricsRegistry
+}
+
+// AddTags adds the provided tags to the provided context. If the provided context already has tag storage, the new tags
+// are appended to the storage in the existing context (which mutates the content of the context) and returns the same
+// context. If the provided context does not store any tags, this call creates and returns a new context that has tag
+// storage and stores the provided tags. If the provided context has any tags already set on it, the provided tags are
+// appended to them. This function does not perform any de-duplication (that is, if a tag in the provided tags has the
+// same key as an existing one, it will still be appended). Note that tags are shared
+func AddTags(ctx context.Context, tags ...Tag) context.Context {
+	if tagsContainer, ok := ctx.Value(tagsKey).(*tagsContainer); ok && tagsContainer != nil {
+		tagsContainer.Tags = append(tagsContainer.Tags, tags...)
+		return ctx
+	}
+	return context.WithValue(ctx, tagsKey, &tagsContainer{
+		Tags: tags,
+	})
+}
+
+// TagsFromContext returns the tags stored on the provided context. May be nil if no tags have been set on the context.
+func TagsFromContext(ctx context.Context) Tags {
+	if tagsContainer, ok := ctx.Value(tagsKey).(*tagsContainer); ok {
+		return tagsContainer.Tags
+	}
+	return nil
+}
+
+type tagsContainer struct {
+	Tags Tags
+}

metrics/context_test.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2018 Palantir Technologies. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package metrics
+
+import (
+	"context"
+	"testing"
+
+	"github.com/rcrowley/go-metrics"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFromContext(t *testing.T) {
+	ctx := context.Background()
+	reg := &rootRegistry{
+		registry: metrics.NewPrefixedRegistry("foo"),
+	}
+
+	ctx = WithRegistry(ctx, reg)
+
+	assert.Equal(t, FromContext(ctx), reg)
+}
+
+func TestDefaultFromContext(t *testing.T) {
+	ctx := context.Background()
+	assert.Equal(t, FromContext(ctx), DefaultMetricsRegistry)
+}

metrics/emit.go

@@ -0,0 +1,26 @@
+// Copyright (c) 2018 Palantir Technologies. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package metrics
+
+import (
+	"context"
+	"time"
+)
+
+// RunEmittingRegistry periodically calls registry.Each with a provided visit function. See the
+// documentation for Registry for the arguments of the visit function. RunEmittingRegistry blocks forever
+// (or until ctx is cancelled) and should be started in its own goroutine.
+func RunEmittingRegistry(ctx context.Context, registry Registry, emitFrequency time.Duration, visitor MetricVisitor) {
+	t := time.NewTicker(emitFrequency)
+	defer t.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+			registry.Each(visitor)
+		}
+	}
+}