windows/svc: workaround-exit mechanism that works for signal-less binaries

pkg/windows/service/service.go

@@ -19,6 +19,9 @@ limitations under the License.
 package service
 
 import (
+	"os"
+	"time"
+
 	"k8s.io/apiserver/pkg/server"
 	"k8s.io/klog"
 
@@ -85,12 +88,24 @@ Loop:
 				// If we do not do this, our main threads won't be notified of the upcoming shutdown.
 				// Since Windows services do not use any console, we cannot simply generate a CTRL_BREAK_EVENT
 				// but need a dedicated notification mechanism.
-				server.RequestShutdown()
+				graceful := server.RequestShutdown()
 
 				// Free up the control handler and let us terminate as gracefully as possible.
 				// If that takes too long, the service controller will kill the remaining threads.
 				// As per https://docs.microsoft.com/en-us/windows/desktop/services/service-control-handler-function
 				s <- svc.Status{State: svc.StopPending}
+
+				// If we cannot exit gracefully, we really only can exit our process, so atleast the
+				// service manager will think that we gracefully exited. At the time of writing this comment this is
+				// needed for applications that do not use signals (e.g. kube-proxy)
+				if !graceful {
+					go func() {
+						// Ensure the SCM was notified (The operation above (send to s) was received and communicated to the
+						// service control manager - so it doesn't look like the service crashes)
+						time.Sleep(1 * time.Second)
+						os.Exit(0)
+					}()
+				}
 				break Loop
 			}
 		}

staging/src/k8s.io/apiserver/pkg/server/signal.go

@@ -22,7 +22,7 @@ import (
 )
 
 var onlyOneSignalHandler = make(chan struct{})
-var shutdownHandler = make(chan os.Signal, 2)
+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
@@ -30,6 +30,8 @@ var shutdownHandler = make(chan os.Signal, 2)
 func SetupSignalHandler() <-chan struct{} {
 	close(onlyOneSignalHandler) // panics when called twice
 
+	shutdownHandler = make(chan os.Signal, 2)
+
 	stop := make(chan struct{})
 	signal.Notify(shutdownHandler, shutdownSignals...)
 	go func() {
@@ -43,9 +45,15 @@ func SetupSignalHandler() <-chan struct{} {
 }
 
 // RequestShutdown emulates a received event that is considered as shutdown signal (SIGTERM/SIGINT)
-func RequestShutdown() {
-	select {
-	case shutdownHandler <- shutdownSignals[0]:
-	default:
+// This returns whether a handler was notified
+func RequestShutdown() bool {
+	if shutdownHandler != nil {
+		select {
+		case shutdownHandler <- shutdownSignals[0]:
+			return true
+		default:
+		}
 	}
+
+	return false
 }