Graceful: Xorm, RepoIndexer, Cron and Others (#9282)

* Change graceful to use a singleton obtained through GetManager instead of a global.
* Graceful: Make TestPullRequests shutdownable
* Graceful: Make the cron tasks graceful
* Graceful: AddTestPullRequest run in graceful ctx
* Graceful: SyncMirrors shutdown
* Graceful: SetDefaultContext for Xorm to be HammerContext
* Avoid starting graceful for migrate commands and checkout
* Graceful: DeliverHooks now can be shutdown
* Fix multiple syncing errors in modules/sync/UniqueQueue &  Make UniqueQueue closable
* Begin the process of making the repo indexer shutdown gracefully

modules/graceful/manager_windows.go

@@ -30,7 +30,8 @@ const (
 	acceptHammerCode = svc.Accepted(hammerCode)
 )
 
-type gracefulManager struct {
+// Manager manages the graceful shutdown process
+type Manager struct {
 	ctx                    context.Context
 	isChild                bool
 	lock                   *sync.RWMutex
@@ -38,27 +39,37 @@ type gracefulManager struct {
 	shutdown               chan struct{}
 	hammer                 chan struct{}
 	terminate              chan struct{}
+	done                   chan struct{}
 	runningServerWaitGroup sync.WaitGroup
 	createServerWaitGroup  sync.WaitGroup
 	terminateWaitGroup     sync.WaitGroup
 }
 
-func newGracefulManager(ctx context.Context) *gracefulManager {
-	manager := &gracefulManager{
+func newGracefulManager(ctx context.Context) *Manager {
+	manager := &Manager{
 		isChild: false,
 		lock:    &sync.RWMutex{},
 		ctx:     ctx,
 	}
 	manager.createServerWaitGroup.Add(numberOfServersToCreate)
-	manager.Run()
+	manager.start()
 	return manager
 }
 
-func (g *gracefulManager) Run() {
+func (g *Manager) start() {
+	// Make channels
+	g.terminate = make(chan struct{})
+	g.shutdown = make(chan struct{})
+	g.hammer = make(chan struct{})
+	g.done = make(chan struct{})
+
+	// Set the running state
 	g.setState(stateRunning)
 	if skip, _ := strconv.ParseBool(os.Getenv("SKIP_MINWINSVC")); skip {
 		return
 	}
+
+	// Make SVC process
 	run := svc.Run
 	isInteractive, err := svc.IsAnInteractiveSession()
 	if err != nil {
@@ -71,8 +82,8 @@ func (g *gracefulManager) 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) {
+// Execute makes Manager implement svc.Handler
+func (g *Manager) 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 {
@@ -141,11 +152,13 @@ hammerLoop:
 	return false, 0
 }
 
-func (g *gracefulManager) RegisterServer() {
+// RegisterServer registers the running of a listening server.
+// Any call to RegisterServer must be matched by a call to ServerDone
+func (g *Manager) RegisterServer() {
 	g.runningServerWaitGroup.Add(1)
 }
 
-func (g *gracefulManager) awaitServer(limit time.Duration) bool {
+func (g *Manager) awaitServer(limit time.Duration) bool {
 	c := make(chan struct{})
 	go func() {
 		defer close(c)