windows/svc: add new package to help create and manage Windows services

Change-Id: I58bb446aaa387b31d8a9ff4217793a170b96a7e2
Reviewed-on: https://go-review.googlesource.com/9104
Reviewed-by: Rob Pike <r@golang.org>

windows/svc/example/service.go

@@ -0,0 +1,82 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build windows
+
+package main
+
+import (
+	"fmt"
+	"time"
+
+	"golang.org/x/sys/windows/svc"
+	"golang.org/x/sys/windows/svc/debug"
+	"golang.org/x/sys/windows/svc/eventlog"
+)
+
+var elog debug.Log
+
+type myservice struct{}
+
+func (m *myservice) Execute(args []string, r <-chan svc.ChangeRequest, changes chan<- svc.Status) (ssec bool, errno uint32) {
+	const cmdsAccepted = svc.AcceptStop | svc.AcceptShutdown | svc.AcceptPauseAndContinue
+	changes <- svc.Status{State: svc.StartPending}
+	fasttick := time.Tick(500 * time.Millisecond)
+	slowtick := time.Tick(2 * time.Second)
+	tick := fasttick
+	changes <- svc.Status{State: svc.Running, Accepts: cmdsAccepted}
+loop:
+	for {
+		select {
+		case <-tick:
+			beep()
+			elog.Info(1, "beep")
+		case c := <-r:
+			switch c.Cmd {
+			case svc.Interrogate:
+				changes <- c.CurrentStatus
+				// Testing deadlock from https://code.google.com/p/winsvc/issues/detail?id=4
+				time.Sleep(100 * time.Millisecond)
+				changes <- c.CurrentStatus
+			case svc.Stop, svc.Shutdown:
+				break loop
+			case svc.Pause:
+				changes <- svc.Status{State: svc.Paused, Accepts: cmdsAccepted}
+				tick = slowtick
+			case svc.Continue:
+				changes <- svc.Status{State: svc.Running, Accepts: cmdsAccepted}
+				tick = fasttick
+			default:
+				elog.Error(1, fmt.Sprintf("unexpected control request #%d", c))
+			}
+		}
+	}
+	changes <- svc.Status{State: svc.StopPending}
+	return
+}
+
+func runService(name string, isDebug bool) {
+	var err error
+	if isDebug {
+		elog = debug.New(name)
+	} else {
+		elog, err = eventlog.Open(name)
+		if err != nil {
+			return
+		}
+	}
+	defer elog.Close()
+
+	elog.Info(1, fmt.Sprintf("starting %s service", name))
+	run := svc.Run
+	if isDebug {
+		run = debug.Run
+	}
+	err = run(name, &myservice{})
+	if err != nil {
+		elog.Error(1, fmt.Sprintf("%s service failed: %v", name, err))
+		return
+	}
+	elog.Info(1, fmt.Sprintf("%s service stopped", name))
+}