Fix CPU hogging bug in Sleep activity.

Heartbeating was incorrectly structured to fire at nanosecond intervals rather
than seconds. Unfortunately this timer would also fire even when heartbeating
was meant ot be disabled.

h/t to @Quinn-With-Two-Ns for spotting the issue.

Author: robholland

activities/activity.go

@@ -14,21 +14,31 @@ type SleepActivityInput struct {
 func SleepActivity(ctx context.Context, input SleepActivityInput) error {
 	sleepTimer := time.After(time.Duration(input.SleepTimeInSeconds) * time.Second)
 	heartbeatTimeout := activity.GetInfo(ctx).HeartbeatTimeout
+
+	// If no heartbeat timeout is set, we don't need heartbeating
 	if heartbeatTimeout == 0 {
-		// If no heartbeat timeout is set, assume we don't want heartbeating.
-		// Set the heartbeat time longer than our sleep time so that we never send a heartbeat.
-		heartbeatTimeout = time.Duration(input.SleepTimeInSeconds) * 2
+		for {
+			select {
+			case <-sleepTimer:
+				return nil
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
 	}
+
+	// Create ticker only when heartbeating is needed
 	heartbeatTick := time.Duration(0.8 * float64(heartbeatTimeout))
-	t := time.NewTicker(heartbeatTick)
+	ticker := time.NewTicker(heartbeatTick)
+	defer ticker.Stop()
 
 	for {
 		select {
 		case <-sleepTimer:
 			return nil
 		case <-ctx.Done():
 			return ctx.Err()
-		case <-t.C:
+		case <-ticker.C:
 			activity.RecordHeartbeat(ctx)
 		}
 	}