istio

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/*
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Copyright 2018 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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    http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package k8sleaderelection
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import (
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	"sync"
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)
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// This file provides abstractions for setting the provider (e.g., prometheus)
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// of metrics.
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type leaderMetricsAdapter interface {
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	leaderOn(name string)
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	leaderOff(name string)
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}
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// GaugeMetric represents a single numerical value that can arbitrarily go up
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// and down.
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type SwitchMetric interface {
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	On(name string)
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	Off(name string)
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}
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type noopMetric struct{}
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func (noopMetric) On(name string)  {}
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func (noopMetric) Off(name string) {}
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// defaultLeaderMetrics expects the caller to lock before setting any metrics.
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type defaultLeaderMetrics struct {
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	// leader's value indicates if the current process is the owner of name lease
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	leader SwitchMetric
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}
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func (m *defaultLeaderMetrics) leaderOn(name string) {
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	if m == nil {
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		return
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	}
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	m.leader.On(name)
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}
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func (m *defaultLeaderMetrics) leaderOff(name string) {
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	if m == nil {
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		return
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	}
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	m.leader.Off(name)
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}
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type noMetrics struct{}
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func (noMetrics) leaderOn(name string)  {}
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func (noMetrics) leaderOff(name string) {}
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// MetricsProvider generates various metrics used by the leader election.
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type MetricsProvider interface {
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	NewLeaderMetric() SwitchMetric
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}
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type noopMetricsProvider struct{}
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func (noopMetricsProvider) NewLeaderMetric() SwitchMetric {
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	return noopMetric{}
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}
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var globalMetricsFactory = leaderMetricsFactory{
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	metricsProvider: noopMetricsProvider{},
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}
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type leaderMetricsFactory struct {
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	metricsProvider MetricsProvider
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	onlyOnce sync.Once
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}
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func (f *leaderMetricsFactory) setProvider(mp MetricsProvider) {
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	f.onlyOnce.Do(func() {
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		f.metricsProvider = mp
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	})
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}
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func (f *leaderMetricsFactory) newLeaderMetrics() leaderMetricsAdapter {
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	mp := f.metricsProvider
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	if mp == (noopMetricsProvider{}) {
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		return noMetrics{}
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	}
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	return &defaultLeaderMetrics{
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		leader: mp.NewLeaderMetric(),
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	}
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}
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// SetProvider sets the metrics provider for all subsequently created work
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// queues. Only the first call has an effect.
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func SetProvider(metricsProvider MetricsProvider) {
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	globalMetricsFactory.setProvider(metricsProvider)
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}
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