Add Graceful shutdown for Windows and hooks for shutdown of goroutines (#8964)

* Graceful Shutdown for windows and others

Restructures modules/graceful, adding shutdown for windows, removing and
replacing the old minwinsvc code.

Creates a new waitGroup - terminate which allows for goroutines to
finish up after the shutdown of the servers.

Shutdown and terminate hooks are added for goroutines.

* Remove unused functions - these can be added in a different PR

* Add startup timeout functionality

* Document STARTUP_TIMEOUT

modules/graceful/manager_windows.go

@@ -0,0 +1,162 @@
+// +build windows
+
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// This code is heavily inspired by the archived gofacebook/gracenet/net.go handler
+
+package graceful
+
+import (
+	"os"
+	"strconv"
+	"sync"
+	"time"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+
+	"golang.org/x/sys/windows/svc"
+	"golang.org/x/sys/windows/svc/debug"
+)
+
+var WindowsServiceName = "gitea"
+
+const (
+	hammerCode       = 128
+	hammerCmd        = svc.Cmd(hammerCode)
+	acceptHammerCode = svc.Accepted(hammerCode)
+)
+
+
+type gracefulManager struct {
+	isChild                bool
+	lock                   *sync.RWMutex
+	state                  state
+	shutdown               chan struct{}
+	hammer                 chan struct{}
+	terminate              chan struct{}
+	runningServerWaitGroup sync.WaitGroup
+	createServerWaitGroup  sync.WaitGroup
+	terminateWaitGroup     sync.WaitGroup
+}
+
+func newGracefulManager() *gracefulManager {
+	manager := &gracefulManager{
+		isChild: false,
+		lock:    &sync.RWMutex{},
+	}
+	manager.createServerWaitGroup.Add(numberOfServersToCreate)
+	manager.Run()
+	return manager
+}
+
+func (g *gracefulManager) Run() {
+	g.setState(stateRunning)
+	if skip, _ := strconv.ParseBool(os.Getenv("SKIP_MINWINSVC")); skip {
+		return
+	}
+	run := svc.Run
+	isInteractive, err := svc.IsAnInteractiveSession()
+	if err != nil {
+		log.Error("Unable to ascertain if running as an Interactive Session: %v", err)
+		return
+	}
+	if isInteractive {
+		run = debug.Run
+	}
+	go run(WindowsServiceName, g)
+}
+
+// Execute makes gracefulManager implement svc.Handler
+func (g *gracefulManager) Execute(args []string, changes <-chan svc.ChangeRequest, status chan<- svc.Status) (svcSpecificEC bool, exitCode uint32) {
+	if setting.StartupTimeout > 0 {
+		status <- svc.Status{State: svc.StartPending}
+	} else {
+		status <- svc.Status{State: svc.StartPending, WaitHint: uint32(setting.StartupTimeout/time.Millisecond)}
+	}
+
+	// Now need to wait for everything to start...
+	if !g.awaitServer(setting.StartupTimeout) {
+		return false, 1
+	}
+
+	// We need to implement some way of svc.AcceptParamChange/svc.ParamChange
+	status <- svc.Status{
+		State:   svc.Running,
+		Accepts: svc.AcceptStop | svc.AcceptShutdown | acceptHammerCode,
+	}
+
+	waitTime := 30 * time.Second
+
+loop:
+	for change := range changes {
+		switch change.Cmd {
+		case svc.Interrogate:
+			status <- change.CurrentStatus
+		case svc.Stop, svc.Shutdown:
+			g.doShutdown()
+			waitTime += setting.GracefulHammerTime
+			break loop
+		case hammerCode:
+			g.doShutdown()
+			g.doHammerTime(0 *time.Second)
+			break loop
+		default:
+			log.Debug("Unexpected control request: %v", change.Cmd)
+		}
+	}
+
+	status <- svc.Status{
+		State: svc.StopPending,
+		WaitHint: uint32(waitTime/time.Millisecond),
+	}
+
+hammerLoop:
+	for {
+		select {
+		case change := <-changes:
+			switch change.Cmd {
+			case svc.Interrogate:
+				status <- change.CurrentStatus
+			case svc.Stop, svc.Shutdown, hammerCmd:
+				g.doHammerTime(0 * time.Second)
+				break hammerLoop
+			default:
+				log.Debug("Unexpected control request: %v", change.Cmd)
+			}
+		case <-g.hammer:
+			break hammerLoop
+		}
+	}
+	return false, 0
+}
+
+func (g *gracefulManager) RegisterServer() {
+	g.runningServerWaitGroup.Add(1)
+}
+
+func (g *gracefulManager) awaitServer(limit time.Duration) bool {
+	c := make(chan struct{})
+	go func() {
+		defer close(c)
+		g.createServerWaitGroup.Wait()
+	}()
+	if limit > 0 {
+		select {
+		case <-c:
+			return true // completed normally
+		case <-time.After(limit):
+			return false // timed out
+		case <-g.IsShutdown():
+			return false
+		}
+	} else {
+		select {
+		case <-c:
+			return true // completed normally
+		case <-g.IsShutdown():
+			return false
+		}
+	}
+}