Improve terminal reuse and attach

Currently attach and the editor do not share the same logic for saving
and restoring the terminal, and are not suitable for nesting (when the
caller wants to create something, attach, and then delete something when
the attach is over).  This commit moves the interrupt protection logic
to a util package and supports nesting interrupt handlers.

pkg/util/interrupt/interrupt.go

@@ -0,0 +1,78 @@
+/*
+Copyright 2016 The Kubernetes Authors All rights reserved.
+
+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 interrupt
+
+import (
+	"os"
+	"os/signal"
+	"sync"
+)
+
+type Handler struct {
+	notify []func()
+	final  func(os.Signal)
+	once   sync.Once
+}
+
+func Chain(handler *Handler, notify ...func()) *Handler {
+	if handler == nil {
+		return New(nil, notify...)
+	}
+	return New(handler.Signal, append(notify, handler.Close)...)
+}
+
+func New(final func(os.Signal), notify ...func()) *Handler {
+	return &Handler{
+		final:  final,
+		notify: notify,
+	}
+}
+
+func (h *Handler) Close() {
+	h.once.Do(func() {
+		for _, fn := range h.notify {
+			fn()
+		}
+	})
+}
+
+func (h *Handler) Signal(s os.Signal) {
+	h.once.Do(func() {
+		for _, fn := range h.notify {
+			fn()
+		}
+		if h.final == nil {
+			os.Exit(0)
+		}
+		h.final(s)
+	})
+}
+
+func (h *Handler) Run(fn func() error) error {
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, childSignals...)
+	defer signal.Stop(ch)
+	go func() {
+		sig, ok := <-ch
+		if !ok {
+			return
+		}
+		h.Signal(sig)
+	}()
+	defer h.Close()
+	return fn()
+}