multi: Add atomic start/stop functions.

Make sure that each subsystem only starts and stop once. This makes
sure we don't close e.g. quit channels twice.

invoices/invoiceregistry.go

@@ -101,6 +101,9 @@ func (r *htlcReleaseEvent) Less(other queue.PriorityQueueItem) bool {
 // created by the daemon. The registry is a thin wrapper around a map in order
 // to ensure that all updates/reads are thread safe.
 type InvoiceRegistry struct {
+	started atomic.Bool
+	stopped atomic.Bool
+
 	sync.RWMutex
 
 	nextClientID uint32 // must be used atomically
@@ -213,33 +216,48 @@ func (i *InvoiceRegistry) scanInvoicesOnStart(ctx context.Context) error {
 
 // Start starts the registry and all goroutines it needs to carry out its task.
 func (i *InvoiceRegistry) Start() error {
-	// Start InvoiceExpiryWatcher and prepopulate it with existing active
-	// invoices.
-	err := i.expiryWatcher.Start(func(hash lntypes.Hash, force bool) error {
-		return i.cancelInvoiceImpl(context.Background(), hash, force)
-	})
+	var err error
+
+	log.Info("InvoiceRegistry starting...")
+
+	if i.started.Swap(true) {
+		return fmt.Errorf("InvoiceRegistry started more than once")
+	}
+	// Start InvoiceExpiryWatcher and prepopulate it with existing
+	// active invoices.
+	err = i.expiryWatcher.Start(
+		func(hash lntypes.Hash, force bool) error {
+			return i.cancelInvoiceImpl(
+				context.Background(), hash, force,
+			)
+		})
 	if err != nil {
 		return err
 	}
 
-	log.Info("InvoiceRegistry starting")
-
 	i.wg.Add(1)
 	go i.invoiceEventLoop()
 
-	// Now scan all pending and removable invoices to the expiry watcher or
-	// delete them.
+	// Now scan all pending and removable invoices to the expiry
+	// watcher or delete them.
 	err = i.scanInvoicesOnStart(context.Background())
 	if err != nil {
 		_ = i.Stop()
-		return err
 	}
 
-	return nil
+	log.Debug("InvoiceRegistry started")
+
+	return err
 }
 
 // Stop signals the registry for a graceful shutdown.
 func (i *InvoiceRegistry) Stop() error {
+	log.Info("InvoiceRegistry shutting down...")
+
+	if i.stopped.Swap(true) {
+		return fmt.Errorf("InvoiceRegistry stopped more than once")
+	}
+
 	log.Info("InvoiceRegistry shutting down...")
 	defer log.Debug("InvoiceRegistry shutdown complete")
 
@@ -248,6 +266,9 @@ func (i *InvoiceRegistry) Stop() error {
 	close(i.quit)
 
 	i.wg.Wait()
+
+	log.Debug("InvoiceRegistry shutdown complete")
+
 	return nil
 }