Initial commit

vendor/github.com/knative/pkg/apis/duck/cached.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2018 The Knative 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 duck
+
+import (
+	"sync"
+
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/client-go/tools/cache"
+)
+
+// CachedInformerFactory implements InformerFactory by delegating to another
+// InformerFactory, but memoizing the results.
+type CachedInformerFactory struct {
+	Delegate InformerFactory
+
+	m     sync.Mutex
+	cache map[schema.GroupVersionResource]*result
+}
+
+// Check that CachedInformerFactory implements InformerFactory.
+var _ InformerFactory = (*CachedInformerFactory)(nil)
+
+// Get implements InformerFactory.
+func (cif *CachedInformerFactory) Get(gvr schema.GroupVersionResource) (cache.SharedIndexInformer, cache.GenericLister, error) {
+	cif.m.Lock()
+	if cif.cache == nil {
+		cif.cache = make(map[schema.GroupVersionResource]*result)
+	}
+	elt, ok := cif.cache[gvr]
+	if !ok {
+		elt = &result{}
+		elt.init = func() {
+			elt.inf, elt.lister, elt.err = cif.Delegate.Get(gvr)
+		}
+		cif.cache[gvr] = elt
+	}
+	// If this were done via "defer", then TestDifferentGVRs will fail.
+	cif.m.Unlock()
+
+	// The call to the delegate could be slow because it syncs informers, so do
+	// this outside of the main lock.
+	return elt.Get()
+}
+
+type result struct {
+	sync.Once
+	init func()
+
+	inf    cache.SharedIndexInformer
+	lister cache.GenericLister
+	err    error
+}
+
+func (t *result) Get() (cache.SharedIndexInformer, cache.GenericLister, error) {
+	t.Do(t.init)
+	return t.inf, t.lister, t.err
+}