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feature_gate.go
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feature_gate.go
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/*
Copyright 2016 The Kubernetes Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package feature
import (
"fmt"
"sort"
"strconv"
"strings"
"sync"
"sync/atomic"
"github.com/golang/glog"
"github.com/spf13/pflag"
)
type Feature string
const (
flagName = "feature-gates"
// allAlphaGate is a global toggle for alpha features. Per-feature key
// values override the default set by allAlphaGate. Examples:
// AllAlpha=false,NewFeature=true will result in newFeature=true
// AllAlpha=true,NewFeature=false will result in newFeature=false
allAlphaGate Feature = "AllAlpha"
)
var (
// The generic features.
defaultFeatures = map[Feature]FeatureSpec{
allAlphaGate: {Default: false, PreRelease: Alpha},
}
// Special handling for a few gates.
specialFeatures = map[Feature]func(known map[Feature]FeatureSpec, enabled map[Feature]bool, val bool){
allAlphaGate: setUnsetAlphaGates,
}
// DefaultFeatureGate is a shared global FeatureGate.
DefaultFeatureGate FeatureGate = NewFeatureGate()
)
type FeatureSpec struct {
Default bool
PreRelease prerelease
}
type prerelease string
const (
// Values for PreRelease.
Alpha = prerelease("ALPHA")
Beta = prerelease("BETA")
GA = prerelease("")
// Deprecated
Deprecated = prerelease("DEPRECATED")
)
// FeatureGate parses and stores flag gates for known features from
// a string like feature1=true,feature2=false,...
type FeatureGate interface {
// AddFlag adds a flag for setting global feature gates to the specified FlagSet.
AddFlag(fs *pflag.FlagSet)
// Set parses and stores flag gates for known features
// from a string like feature1=true,feature2=false,...
Set(value string) error
// SetFromMap stores flag gates for known features from a map[string]bool or returns an error
SetFromMap(m map[string]bool) error
// Enabled returns true if the key is enabled.
Enabled(key Feature) bool
// Add adds features to the featureGate.
Add(features map[Feature]FeatureSpec) error
// KnownFeatures returns a slice of strings describing the FeatureGate's known features.
KnownFeatures() []string
}
// featureGate implements FeatureGate as well as pflag.Value for flag parsing.
type featureGate struct {
special map[Feature]func(map[Feature]FeatureSpec, map[Feature]bool, bool)
// lock guards writes to known, enabled, and reads/writes of closed
lock sync.Mutex
// known holds a map[Feature]FeatureSpec
known *atomic.Value
// enabled holds a map[Feature]bool
enabled *atomic.Value
// closed is set to true when AddFlag is called, and prevents subsequent calls to Add
closed bool
}
func setUnsetAlphaGates(known map[Feature]FeatureSpec, enabled map[Feature]bool, val bool) {
for k, v := range known {
if v.PreRelease == Alpha {
if _, found := enabled[k]; !found {
enabled[k] = val
}
}
}
}
// Set, String, and Type implement pflag.Value
var _ pflag.Value = &featureGate{}
func NewFeatureGate() *featureGate {
known := map[Feature]FeatureSpec{}
for k, v := range defaultFeatures {
known[k] = v
}
knownValue := &atomic.Value{}
knownValue.Store(known)
enabled := map[Feature]bool{}
enabledValue := &atomic.Value{}
enabledValue.Store(enabled)
f := &featureGate{
known: knownValue,
special: specialFeatures,
enabled: enabledValue,
}
return f
}
// Set parses a string of the form "key1=value1,key2=value2,..." into a
// map[string]bool of known keys or returns an error.
func (f *featureGate) Set(value string) error {
f.lock.Lock()
defer f.lock.Unlock()
// Copy existing state
known := map[Feature]FeatureSpec{}
for k, v := range f.known.Load().(map[Feature]FeatureSpec) {
known[k] = v
}
enabled := map[Feature]bool{}
for k, v := range f.enabled.Load().(map[Feature]bool) {
enabled[k] = v
}
for _, s := range strings.Split(value, ",") {
if len(s) == 0 {
continue
}
arr := strings.SplitN(s, "=", 2)
k := Feature(strings.TrimSpace(arr[0]))
featureSpec, ok := known[k]
if !ok {
return fmt.Errorf("unrecognized key: %s", k)
}
if len(arr) != 2 {
return fmt.Errorf("missing bool value for %s", k)
}
v := strings.TrimSpace(arr[1])
boolValue, err := strconv.ParseBool(v)
if err != nil {
return fmt.Errorf("invalid value of %s: %s, err: %v", k, v, err)
}
enabled[k] = boolValue
if boolValue && featureSpec.PreRelease == Deprecated {
glog.Warningf("enabling deprecated feature gate %s", k)
}
// Handle "special" features like "all alpha gates"
if fn, found := f.special[k]; found {
fn(known, enabled, boolValue)
}
}
// Persist changes
f.known.Store(known)
f.enabled.Store(enabled)
glog.Infof("feature gates: %v", enabled)
return nil
}
// SetFromMap stores flag gates for known features from a map[string]bool or returns an error
func (f *featureGate) SetFromMap(m map[string]bool) error {
f.lock.Lock()
defer f.lock.Unlock()
// Copy existing state
known := map[Feature]FeatureSpec{}
for k, v := range f.known.Load().(map[Feature]FeatureSpec) {
known[k] = v
}
enabled := map[Feature]bool{}
for k, v := range f.enabled.Load().(map[Feature]bool) {
enabled[k] = v
}
for k, v := range m {
k := Feature(k)
_, ok := known[k]
if !ok {
return fmt.Errorf("unrecognized key: %s", k)
}
enabled[k] = v
// Handle "special" features like "all alpha gates"
if fn, found := f.special[k]; found {
fn(known, enabled, v)
}
}
// Persist changes
f.known.Store(known)
f.enabled.Store(enabled)
glog.Infof("feature gates: %v", f.enabled)
return nil
}
// String returns a string containing all enabled feature gates, formatted as "key1=value1,key2=value2,...".
func (f *featureGate) String() string {
pairs := []string{}
for k, v := range f.enabled.Load().(map[Feature]bool) {
pairs = append(pairs, fmt.Sprintf("%s=%t", k, v))
}
sort.Strings(pairs)
return strings.Join(pairs, ",")
}
func (f *featureGate) Type() string {
return "mapStringBool"
}
// Add adds features to the featureGate.
func (f *featureGate) Add(features map[Feature]FeatureSpec) error {
f.lock.Lock()
defer f.lock.Unlock()
if f.closed {
return fmt.Errorf("cannot add a feature gate after adding it to the flag set")
}
// Copy existing state
known := map[Feature]FeatureSpec{}
for k, v := range f.known.Load().(map[Feature]FeatureSpec) {
known[k] = v
}
for name, spec := range features {
if existingSpec, found := known[name]; found {
if existingSpec == spec {
continue
}
return fmt.Errorf("feature gate %q with different spec already exists: %v", name, existingSpec)
}
known[name] = spec
}
// Persist updated state
f.known.Store(known)
return nil
}
// Enabled returns true if the key is enabled.
func (f *featureGate) Enabled(key Feature) bool {
if v, ok := f.enabled.Load().(map[Feature]bool)[key]; ok {
return v
}
return f.known.Load().(map[Feature]FeatureSpec)[key].Default
}
// AddFlag adds a flag for setting global feature gates to the specified FlagSet.
func (f *featureGate) AddFlag(fs *pflag.FlagSet) {
f.lock.Lock()
f.closed = true
f.lock.Unlock()
known := f.KnownFeatures()
fs.Var(f, flagName, ""+
"A set of key=value pairs that describe feature gates for alpha/experimental features. "+
"Options are:\n"+strings.Join(known, "\n"))
}
// KnownFeatures returns a slice of strings describing the FeatureGate's known features.
func (f *featureGate) KnownFeatures() []string {
var known []string
for k, v := range f.known.Load().(map[Feature]FeatureSpec) {
pre := ""
if v.PreRelease != GA {
pre = fmt.Sprintf("%s - ", v.PreRelease)
}
known = append(known, fmt.Sprintf("%s=true|false (%sdefault=%t)", k, pre, v.Default))
}
sort.Strings(known)
return known
}