libgo/go/runtime/pprof/label.go

   1 // Copyright 2016 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package pprof
   6
   7 import (
   8         "context"
   9 )
  10
  11 type label struct {
  12         key   string
  13         value string
  14 }
  15
  16 // LabelSet is a set of labels.
  17 type LabelSet struct {
  18         list []label
  19 }
  20
  21 // labelContextKey is the type of contextKeys used for profiler labels.
  22 type labelContextKey struct{}
  23
  24 func labelValue(ctx context.Context) labelMap {
  25         labels, _ := ctx.Value(labelContextKey{}).(*labelMap)
  26         if labels == nil {
  27                 return labelMap(nil)
  28         }
  29         return *labels
  30 }
  31
  32 // labelMap is the representation of the label set held in the context type.
  33 // This is an initial implementation, but it will be replaced with something
  34 // that admits incremental immutable modification more efficiently.
  35 type labelMap map[string]string
  36
  37 // WithLabels returns a new context.Context with the given labels added.
  38 // A label overwrites a prior label with the same key.
  39 func WithLabels(ctx context.Context, labels LabelSet) context.Context {
  40         childLabels := make(labelMap)
  41         parentLabels := labelValue(ctx)
  42         // TODO(matloob): replace the map implementation with something
  43         // more efficient so creating a child context WithLabels doesn't need
  44         // to clone the map.
  45         for k, v := range parentLabels {
  46                 childLabels[k] = v
  47         }
  48         for _, label := range labels.list {
  49                 childLabels[label.key] = label.value
  50         }
  51         return context.WithValue(ctx, labelContextKey{}, &childLabels)
  52 }
  53
  54 // Labels takes an even number of strings representing key-value pairs
  55 // and makes a LabelSet containing them.
  56 // A label overwrites a prior label with the same key.
  57 func Labels(args ...string) LabelSet {
  58         if len(args)%2 != 0 {
  59                 panic("uneven number of arguments to pprof.Labels")
  60         }
  61         labels := LabelSet{}
  62         for i := 0; i+1 < len(args); i += 2 {
  63                 labels.list = append(labels.list, label{key: args[i], value: args[i+1]})
  64         }
  65         return labels
  66 }
  67
  68 // Label returns the value of the label with the given key on ctx, and a boolean indicating
  69 // whether that label exists.
  70 func Label(ctx context.Context, key string) (string, bool) {
  71         ctxLabels := labelValue(ctx)
  72         v, ok := ctxLabels[key]
  73         return v, ok
  74 }
  75
  76 // ForLabels invokes f with each label set on the context.
  77 // The function f should return true to continue iteration or false to stop iteration early.
  78 func ForLabels(ctx context.Context, f func(key, value string) bool) {
  79         ctxLabels := labelValue(ctx)
  80         for k, v := range ctxLabels {
  81                 if !f(k, v) {
  82                         break
  83                 }
  84         }
  85 }