Source: label.go in package runtime/pprof


package pprof

import (
	"context"
	"fmt"
	"sort"
	"strings"
)

type label struct {
	key   string
	value string
}

LabelSet is a set of labels.

type LabelSet struct {
	list []label
}

labelContextKey is the type of contextKeys used for profiler labels.

type labelContextKey struct{}

func labelValue(ctx context.Context) labelMap {
	labels, _ := ctx.Value(labelContextKey{}).(*labelMap)
	if labels == nil {
		return labelMap(nil)
	}
	return *labels
}

labelMap is the representation of the label set held in the context type. This is an initial implementation, but it will be replaced with something that admits incremental immutable modification more efficiently.

type labelMap map[string]string

String statisfies Stringer and returns key, value pairs in a consistent order.

func (l *labelMap) String() string {
	if l == nil {
		return ""
	}
	keyVals := make([]string, 0, len(*l))

	for k, v := range *l {
		keyVals = append(keyVals, fmt.Sprintf("%q:%q", k, v))
	}

	sort.Strings(keyVals)

	return "{" + strings.Join(keyVals, ", ") + "}"
}

WithLabels returns a new context.Context with the given labels added. A label overwrites a prior label with the same key.

func WithLabels(ctx context.Context, labels LabelSet) context.Context {
	childLabels := make(labelMap)

TODO(matloob): replace the map implementation with something more efficient so creating a child context WithLabels doesn't need to clone the map.

	for k, v := range parentLabels {
		childLabels[k] = v
	}
	for _, label := range labels.list {
		childLabels[label.key] = label.value
	}
	return context.WithValue(ctx, labelContextKey{}, &childLabels)
}

Labels takes an even number of strings representing key-value pairs and makes a LabelSet containing them. A label overwrites a prior label with the same key. Currently only the CPU and goroutine profiles utilize any labels information. See https://golang.org/issue/23458 for details.

func Labels(args ...string) LabelSet {
	if len(args)%2 != 0 {
		panic("uneven number of arguments to pprof.Labels")
	}
	list := make([]label, 0, len(args)/2)
	for i := 0; i+1 < len(args); i += 2 {
		list = append(list, label{key: args[i], value: args[i+1]})
	}
	return LabelSet{list: list}
}

Label returns the value of the label with the given key on ctx, and a boolean indicating whether that label exists.

func Label(ctx context.Context, key string) (string, bool) {
	ctxLabels := labelValue(ctx)
	v, ok := ctxLabels[key]
	return v, ok
}

ForLabels invokes f with each label set on the context. The function f should return true to continue iteration or false to stop iteration early.

func ForLabels(ctx context.Context, f func(key, value string) bool) {
	ctxLabels := labelValue(ctx)
	for k, v := range ctxLabels {
		if !f(k, v) {
			break
		}
	}