apiserver: move the signal handlers into a stdlib-only leaf package

k8s.io/apiserver/pkg/server/signals now owns the shared SIGTERM/SIGINT
handler. server keeps SetupSignalHandler, SetupSignalContext and
RequestShutdown as wrappers, so existing callers and the single
shutdown state are unchanged. pkg/windows/service imports the leaf,
which takes the generic API server, and with it the CEL stack, out of
kube-proxy.exe.

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

pkg/windows/service/service.go

@@ -24,7 +24,7 @@ import (
 	"time"
 	"unsafe"
 
-	"k8s.io/apiserver/pkg/server"
+	"k8s.io/apiserver/pkg/server/signals"
 	"k8s.io/klog/v2"
 
 	"golang.org/x/sys/windows"
@@ -171,7 +171,7 @@ 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.
-				graceful := server.RequestShutdown()
+				graceful := signals.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.

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

@@ -18,52 +18,23 @@ package server
 
 import (
 	"context"
-	"os"
-	"os/signal"
+
+	"k8s.io/apiserver/pkg/server/signals"
 )
 
-var onlyOneSignalHandler = make(chan struct{})
-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.
+// SetupSignalHandler is signals.SetupSignalHandler. The wrappers in this file
+// keep the published API and the single shared shutdown state for existing
+// callers.
 func SetupSignalHandler() <-chan struct{} {
-	return SetupSignalContext().Done()
+	return signals.SetupSignalHandler()
 }
 
-// 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.
+// SetupSignalContext is signals.SetupSignalContext.
 func SetupSignalContext() context.Context {
-	close(onlyOneSignalHandler) // panics when called twice
-
-	shutdownHandler = make(chan os.Signal, 2)
-
-	ctx, cancel := context.WithCancel(context.Background())
-	signal.Notify(shutdownHandler, shutdownSignals...)
-	go func() {
-		<-shutdownHandler
-		cancel()
-		<-shutdownHandler
-		os.Exit(1) // second signal. Exit directly.
-	}()
-
-	return ctx
+	return signals.SetupSignalContext()
 }
 
-// RequestShutdown emulates a received event that is considered as shutdown signal (SIGTERM/SIGINT)
-// This returns whether a handler was notified
+// RequestShutdown is signals.RequestShutdown.
 func RequestShutdown() bool {
-	if shutdownHandler != nil {
-		select {
-		case shutdownHandler <- shutdownSignals[0]:
-			return true
-		default:
-		}
-	}
-
-	return false
+	return signals.RequestShutdown()
 }

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

@@ -0,0 +1,71 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package signals installs the shared SIGTERM and SIGINT shutdown handler.
+// It depends only on the standard library.
+package signals
+
+import (
+	"context"
+	"os"
+	"os/signal"
+)
+
+var onlyOneSignalHandler = make(chan struct{})
+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)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	signal.Notify(shutdownHandler, shutdownSignals...)
+	go func() {
+		<-shutdownHandler
+		cancel()
+		<-shutdownHandler
+		os.Exit(1) // second signal. Exit directly.
+	}()
+
+	return ctx
+}
+
+// RequestShutdown emulates a received event that is considered as shutdown signal (SIGTERM/SIGINT)
+// This returns whether a handler was notified
+func RequestShutdown() bool {
+	if shutdownHandler != nil {
+		select {
+		case shutdownHandler <- shutdownSignals[0]:
+			return true
+		default:
+		}
+	}
+
+	return false
+}

staging/src/k8s.io/apiserver/pkg/server/signals/signal_posix.go

@@ -16,7 +16,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package server
+package signals
 
 import (
 	"os"

staging/src/k8s.io/apiserver/pkg/server/signals/signal_windows.go

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package server
+package signals
 
 import (
 	"os"