make Kubelet bootstrap certificate signal aware

Kubernetes-commit: db7194177538d5efc84af621c4400174a2836b3b

pkg/server/signal.go

@@ -17,6 +17,7 @@ limitations under the License.
 package server
 
 import (
+	"context"
 	"os"
 	"os/signal"
 )
@@ -27,21 +28,30 @@ var shutdownHandler chan os.Signal
 // SetupSignalHandler registered for SIGTERM and SIGINT. A stop channel is returned
 // which is closed on one of these signals. If a second signal is caught, the program
 // is terminated with exit code 1.
+// Only one of SetupSignalContext and SetupSignalHandler should be called, and only can
+// be called once.
 func SetupSignalHandler() <-chan struct{} {
+	return SetupSignalContext().Done()
+}
+
+// SetupSignalContext is same as SetupSignalHandler, but a context.Context is returned.
+// Only one of SetupSignalContext and SetupSignalHandler should be called, and only can
+// be called once.
+func SetupSignalContext() context.Context {
 	close(onlyOneSignalHandler) // panics when called twice
 
 	shutdownHandler = make(chan os.Signal, 2)
 
-	stop := make(chan struct{})
+	ctx, cancel := context.WithCancel(context.Background())
 	signal.Notify(shutdownHandler, shutdownSignals...)
 	go func() {
 		<-shutdownHandler
-		close(stop)
+		cancel()
 		<-shutdownHandler
 		os.Exit(1) // second signal. Exit directly.
 	}()
 
-	return stop
+	return ctx
 }
 
 // RequestShutdown emulates a received event that is considered as shutdown signal (SIGTERM/SIGINT)