only allow starting a source once

Signed-off-by: Tim Ramlot <42113979+inteon@users.noreply.github.com>

pkg/controller/controller_test.go

@@ -79,7 +79,7 @@ var _ = Describe("controller.Controller", func() {
 
 			ctx, cancel := context.WithCancel(context.Background())
 			watchChan := make(chan event.GenericEvent, 1)
-			watch := source.Channel(watchChan, &handler.EnqueueRequestForObject{})
+			watch := source.Channel(source.NewChannelBroadcaster(watchChan), &handler.EnqueueRequestForObject{})
 			watchChan <- event.GenericEvent{Object: &corev1.Pod{}}
 
 			reconcileStarted := make(chan struct{})

pkg/internal/controller/controller_test.go

@@ -227,7 +227,7 @@ var _ = Describe("controller", func() {
 			}
 
 			ins := source.Channel(
-				ch,
+				source.NewChannelBroadcaster(ch),
 				handler.Funcs{
 					GenericFunc: func(ctx context.Context, evt event.GenericEvent, q workqueue.RateLimitingInterface) {
 						defer GinkgoRecover()
@@ -248,7 +248,7 @@ var _ = Describe("controller", func() {
 			<-processed
 		})
 
-		It("should error when channel source is not specified", func() {
+		It("should error when ChannelBroadcaster is not specified", func() {
 			ctx, cancel := context.WithCancel(context.Background())
 			defer cancel()
 
@@ -257,7 +257,7 @@ var _ = Describe("controller", func() {
 
 			e := ctrl.Start(ctx)
 			Expect(e).To(HaveOccurred())
-			Expect(e.Error()).To(ContainSubstring("must specify Channel.Source"))
+			Expect(e.Error()).To(ContainSubstring("must create Channel with a non-nil broadcaster"))
 		})
 
 		It("should call Start on sources with the appropriate EventHandler, Queue, and Predicates", func() {

pkg/internal/source/kind.go

@@ -1,10 +1,27 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+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 internal
 
 import (
 	"context"
 	"errors"
 	"fmt"
 	"reflect"
+	"sync"
 	"time"
 
 	"k8s.io/apimachinery/pkg/api/meta"
@@ -30,6 +47,9 @@ type Kind[T client.Object] struct {
 
 	Predicates []predicate.TypedPredicate[T]
 
+	mu        sync.RWMutex
+	isStarted bool
+
 	// startedErr may contain an error if one was encountered during startup. If its closed and does not
 	// contain an error, startup and syncing finished.
 	startedErr  chan error
@@ -40,14 +60,21 @@ type Kind[T client.Object] struct {
 // to enqueue reconcile.Requests.
 func (ks *Kind[T]) Start(ctx context.Context, queue workqueue.RateLimitingInterface) error {
 	if isNil(ks.Type) {
-		return fmt.Errorf("must create Kind with a non-nil object")
+		return fmt.Errorf("must create Kind with a non-nil type")
 	}
 	if isNil(ks.Cache) {
 		return fmt.Errorf("must create Kind with a non-nil cache")
 	}
 	if isNil(ks.Handler) {
-		return errors.New("must create Kind with non-nil handler")
+		return errors.New("must create Kind with a non-nil handler")
+	}
+
+	ks.mu.Lock()
+	defer ks.mu.Unlock()
+	if ks.isStarted {
+		return fmt.Errorf("cannot start an already started Kind source")
 	}
+	ks.isStarted = true
 
 	// cache.GetInformer will block until its context is cancelled if the cache was already started and it can not
 	// sync that informer (most commonly due to RBAC issues).

pkg/source/example_test.go

@@ -44,7 +44,7 @@ func ExampleChannel() {
 
 	err := ctrl.Watch(
 		source.Channel(
-			events,
+			source.NewChannelBroadcaster(events),
 			&handler.EnqueueRequestForObject{},
 		),
 	)