From 79cc4033c791cf0da7e9f57f3ab3dac2a3a8664e Mon Sep 17 00:00:00 2001
From: Mikhail Mazurskiy <mmazurskiy@atlassian.com>
Date: Mon, 12 Feb 2018 20:48:53 +1100
Subject: [PATCH] Cancellable leader election with channels

Kubernetes-commit: 1d99fff1acb1503755b94d4c72e6dedd35c2d249
---
 tools/leaderelection/leaderelection.go | 79 +++++++++++++++++++-------
 1 file changed, 58 insertions(+), 21 deletions(-)

diff --git a/tools/leaderelection/leaderelection.go b/tools/leaderelection/leaderelection.go
index aed55574..cf56069d 100644
--- a/tools/leaderelection/leaderelection.go
+++ b/tools/leaderelection/leaderelection.go
@@ -51,6 +51,7 @@ package leaderelection
 import (
 	"fmt"
 	"reflect"
+	"sync"
 	"time"
 
 	"k8s.io/apimachinery/pkg/api/errors"
@@ -145,26 +146,28 @@ type LeaderElector struct {
 }
 
 // Run starts the leader election loop
-func (le *LeaderElector) Run() {
+func (le *LeaderElector) Run(stop <-chan struct{}) {
 	defer func() {
 		runtime.HandleCrash()
 		le.config.Callbacks.OnStoppedLeading()
 	}()
-	le.acquire()
-	stop := make(chan struct{})
-	go le.config.Callbacks.OnStartedLeading(stop)
-	le.renew()
-	close(stop)
+	if !le.acquire(stop) {
+		return // stop signalled done
+	}
+	internalStop := make(chan struct{})
+	defer close(internalStop)
+	go le.config.Callbacks.OnStartedLeading(internalStop)
+	le.renew(stop)
 }
 
 // RunOrDie starts a client with the provided config or panics if the config
 // fails to validate.
-func RunOrDie(lec LeaderElectionConfig) {
+func RunOrDie(stop <-chan struct{}, lec LeaderElectionConfig) {
 	le, err := NewLeaderElector(lec)
 	if err != nil {
 		panic(err)
 	}
-	le.Run()
+	le.Run(stop)
 }
 
 // GetLeader returns the identity of the last observed leader or returns the empty string if
@@ -178,13 +181,23 @@ func (le *LeaderElector) IsLeader() bool {
 	return le.observedRecord.HolderIdentity == le.config.Lock.Identity()
 }
 
-// acquire loops calling tryAcquireOrRenew and returns immediately when tryAcquireOrRenew succeeds.
-func (le *LeaderElector) acquire() {
-	stop := make(chan struct{})
+// acquire loops calling tryAcquireOrRenew and returns true immediately when tryAcquireOrRenew succeeds.
+// Returns false if stop signals done.
+func (le *LeaderElector) acquire(stop <-chan struct{}) bool {
+	tmpStop := make(chan struct{})
+	once := sync.Once{}
+	go func() {
+		select {
+		case <-stop:
+			once.Do(func() { close(tmpStop) })
+		case <-tmpStop:
+		}
+	}()
+	succeeded := false
 	desc := le.config.Lock.Describe()
 	glog.Infof("attempting to acquire leader lease  %v...", desc)
 	wait.JitterUntil(func() {
-		succeeded := le.tryAcquireOrRenew()
+		succeeded = le.tryAcquireOrRenew()
 		le.maybeReportTransition()
 		if !succeeded {
 			glog.V(4).Infof("failed to acquire lease %v", desc)
@@ -192,17 +205,41 @@ func (le *LeaderElector) acquire() {
 		}
 		le.config.Lock.RecordEvent("became leader")
 		glog.Infof("successfully acquired lease %v", desc)
-		close(stop)
-	}, le.config.RetryPeriod, JitterFactor, true, stop)
+		once.Do(func() { close(tmpStop) })
+	}, le.config.RetryPeriod, JitterFactor, true, tmpStop)
+	return succeeded
 }
 
-// renew loops calling tryAcquireOrRenew and returns immediately when tryAcquireOrRenew fails.
-func (le *LeaderElector) renew() {
-	stop := make(chan struct{})
+// renew loops calling tryAcquireOrRenew and returns immediately when tryAcquireOrRenew fails or ctx signals done.
+func (le *LeaderElector) renew(stop <-chan struct{}) {
+	tmpStop := make(chan struct{})
+	once := sync.Once{}
+	go func() {
+		select {
+		case <-stop:
+			once.Do(func() { close(tmpStop) })
+		case <-tmpStop:
+		}
+	}()
 	wait.Until(func() {
-		err := wait.Poll(le.config.RetryPeriod, le.config.RenewDeadline, func() (bool, error) {
+		// PollUntil() sleeps for "interval" duration before calling the function so we need to increase the timeout by le.config.RetryPeriod
+		t := time.NewTimer(le.config.RetryPeriod + le.config.RenewDeadline)
+		defer t.Stop()
+		internalStop := make(chan struct{})
+		internalOnce := sync.Once{}
+		defer internalOnce.Do(func() { close(internalStop) })
+		go func() {
+			select {
+			case <-tmpStop:
+				internalOnce.Do(func() { close(internalStop) })
+			case <-t.C:
+				internalOnce.Do(func() { close(internalStop) })
+			case <-internalStop:
+			}
+		}()
+		err := wait.PollUntil(le.config.RetryPeriod, func() (bool, error) {
 			return le.tryAcquireOrRenew(), nil
-		})
+		}, internalStop)
 		le.maybeReportTransition()
 		desc := le.config.Lock.Describe()
 		if err == nil {
@@ -211,8 +248,8 @@ func (le *LeaderElector) renew() {
 		}
 		le.config.Lock.RecordEvent("stopped leading")
 		glog.Infof("failed to renew lease %v: %v", desc, err)
-		close(stop)
-	}, 0, stop)
+		once.Do(func() { close(tmpStop) })
+	}, 0, tmpStop)
 }
 
 // tryAcquireOrRenew tries to acquire a leader lease if it is not already acquired,