Fix regression from #14623 - use debug SVC handler only on interactive sessions (#15210) (#15211)

Backport #15210

Unfortunately #14623 changed from the deprecated IsInteractiveSession to
IsWindowsService without recognising that they are the complement of
each other.

This means that Windows SVC control is not working correctly. This PR
adds some Tracing statements but also fixes the bug.

Fix #15159

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/graceful/manager_windows.go

@@ -68,17 +68,19 @@ func (g *Manager) start() {
 	// Set the running state
 	g.setState(stateRunning)
 	if skip, _ := strconv.ParseBool(os.Getenv("SKIP_MINWINSVC")); skip {
+		log.Trace("Skipping SVC check as SKIP_MINWINSVC is set")
 		return
 	}
 
 	// Make SVC process
 	run := svc.Run
-	isInteractive, err := svc.IsWindowsService()
+	isWindowsService, err := svc.IsWindowsService()
 	if err != nil {
-		log.Error("Unable to ascertain if running as an Interactive Session: %v", err)
+		log.Error("Unable to ascertain if running as an Windows Service: %v", err)
 		return
 	}
-	if isInteractive {
+	if !isWindowsService {
+		log.Trace("Not running a service ... using the debug SVC manager")
 		run = debug.Run
 	}
 	go func() {
@@ -94,38 +96,49 @@ func (g *Manager) Execute(args []string, changes <-chan svc.ChangeRequest, statu
 		status <- svc.Status{State: svc.StartPending, WaitHint: uint32(setting.StartupTimeout / time.Millisecond)}
 	}
 
+	log.Trace("Awaiting server start-up")
 	// Now need to wait for everything to start...
 	if !g.awaitServer(setting.StartupTimeout) {
+		log.Trace("... start-up failed ... Stopped")
 		return false, 1
 	}
 
+	log.Trace("Sending Running state to SVC")
+
 	// We need to implement some way of svc.AcceptParamChange/svc.ParamChange
 	status <- svc.Status{
 		State:   svc.Running,
 		Accepts: svc.AcceptStop | svc.AcceptShutdown | acceptHammerCode,
 	}
 
+	log.Trace("Started")
+
 	waitTime := 30 * time.Second
 
 loop:
 	for {
 		select {
 		case <-g.ctx.Done():
+			log.Trace("Shutting down")
 			g.DoGracefulShutdown()
 			waitTime += setting.GracefulHammerTime
 			break loop
 		case <-g.shutdownRequested:
+			log.Trace("Shutting down")
 			waitTime += setting.GracefulHammerTime
 			break loop
 		case change := <-changes:
 			switch change.Cmd {
 			case svc.Interrogate:
+				log.Trace("SVC sent interrogate")
 				status <- change.CurrentStatus
 			case svc.Stop, svc.Shutdown:
+				log.Trace("SVC requested shutdown - shutting down")
 				g.DoGracefulShutdown()
 				waitTime += setting.GracefulHammerTime
 				break loop
 			case hammerCode:
+				log.Trace("SVC requested hammer - shutting down and hammering immediately")
 				g.DoGracefulShutdown()
 				g.DoImmediateHammer()
 				break loop
@@ -134,6 +147,8 @@ loop:
 			}
 		}
 	}
+
+	log.Trace("Sending StopPending state to SVC")
 	status <- svc.Status{
 		State:    svc.StopPending,
 		WaitHint: uint32(waitTime / time.Millisecond),
@@ -145,8 +160,10 @@ hammerLoop:
 		case change := <-changes:
 			switch change.Cmd {
 			case svc.Interrogate:
+				log.Trace("SVC sent interrogate")
 				status <- change.CurrentStatus
 			case svc.Stop, svc.Shutdown, hammerCmd:
+				log.Trace("SVC requested hammer - hammering immediately")
 				g.DoImmediateHammer()
 				break hammerLoop
 			default:
@@ -156,6 +173,8 @@ hammerLoop:
 			break hammerLoop
 		}
 	}
+
+	log.Trace("Stopped")
 	return false, 0
 }