go label 源码
golang label 代码
文件路径：/src/runtime/pprof/label.go
// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
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 satisfies 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)
parentLabels := labelValue(ctx)
// 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
}
}
}
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