From 75b76488d450253a8190f95022e9b19fbc76e8e3 Mon Sep 17 00:00:00 2001
From: Tristan Nicholls <tvkn@users.noreply.github.com>
Date: Thu, 5 Jan 2023 20:37:49 +0100
Subject: [PATCH] fix(externalclock): fix setTimestamp racing condition

---
 externalclock/clock.go | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/externalclock/clock.go b/externalclock/clock.go
index bb92f98..a484259 100644
--- a/externalclock/clock.go
+++ b/externalclock/clock.go
@@ -15,19 +15,21 @@ import (
 )
 
 type Clock struct {
-	Logger        logr.Logger
-	timestampChan chan time.Time
-	timeMutex     sync.Mutex
-	currentTime   time.Time
-	tickerMutex   sync.RWMutex
-	tickers       map[string]*ticker
+	Logger           logr.Logger
+	timestampChan    chan time.Time // synchronization SetTimestamp -> Run
+	timestampUpdated chan struct{}  // synchronization Run -> SetTimestamp
+	timeMutex        sync.Mutex
+	currentTime      time.Time
+	tickerMutex      sync.RWMutex
+	tickers          map[string]*ticker
 }
 
 func New(logger logr.Logger, initialTime time.Time) *Clock {
 	c := &Clock{
-		Logger:        logger,
-		timestampChan: make(chan time.Time),
-		tickers:       map[string]*ticker{},
+		Logger:           logger,
+		timestampChan:    make(chan time.Time),
+		tickers:          map[string]*ticker{},
+		timestampUpdated: make(chan struct{}),
 	}
 	c.currentTime = initialTime
 	return c
@@ -35,6 +37,7 @@ func New(logger logr.Logger, initialTime time.Time) *Clock {
 
 func (g *Clock) SetTimestamp(t time.Time) {
 	g.timestampChan <- t
+	<-g.timestampUpdated // wait for time to be set before returning
 }
 
 func (g *Clock) NumberOfTriggers() int {
@@ -53,6 +56,10 @@ func (g *Clock) Run(ctx context.Context) error {
 		case recvTime := <-g.timestampChan:
 			g.timeMutex.Lock()
 			g.tickerMutex.RLock()
+
+			g.currentTime = recvTime         // ok to set early since reading is locked while in here.
+			g.timestampUpdated <- struct{}{} // notify SetTimestamp.
+
 			for _, tickerInstance := range g.tickers {
 				if !tickerInstance.IsDurationReached(recvTime) {
 					continue
@@ -69,7 +76,6 @@ func (g *Clock) Run(ctx context.Context) error {
 					g.Logger.V(1).Info("ticker dropped message", "caller", tickerInstance.caller)
 				}
 			}
-			g.setTime(recvTime)
 			g.timeMutex.Unlock()
 			g.tickerMutex.RUnlock()
 		}
@@ -82,11 +88,6 @@ func (g *Clock) getTime() time.Time {
 	return g.currentTime
 }
 
-func (g *Clock) setTime(newTime time.Time) {
-	// note: mutex should be locked when arriving here.
-	g.currentTime = newTime
-}
-
 func (g *Clock) After(duration time.Duration) <-chan time.Time {
 	_, file, no, ok := runtime.Caller(1)
 	var calledFrom string