vendor files

vendor/k8s.io/kubernetes/pkg/volume/metrics_cached.go

@@ -0,0 +1,74 @@
+/*
+Copyright 2014 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 volume
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+var _ MetricsProvider = &cachedMetrics{}
+
+// cachedMetrics represents a MetricsProvider that wraps another provider and
+// caches the result.
+type cachedMetrics struct {
+	wrapped       MetricsProvider
+	resultError   error
+	resultMetrics *Metrics
+	once          cacheOnce
+}
+
+// NewCachedMetrics creates a new cachedMetrics wrapping another
+// MetricsProvider and caching the results.
+func NewCachedMetrics(provider MetricsProvider) MetricsProvider {
+	return &cachedMetrics{wrapped: provider}
+}
+
+// GetMetrics runs the wrapped metrics provider's GetMetrics methd once and
+// caches the result. Will not cache result if there is an error.
+// See MetricsProvider.GetMetrics
+func (md *cachedMetrics) GetMetrics() (*Metrics, error) {
+	md.once.cache(func() error {
+		md.resultMetrics, md.resultError = md.wrapped.GetMetrics()
+		return md.resultError
+	})
+	return md.resultMetrics, md.resultError
+}
+
+// Copied from sync.Once but we don't want to cache the results if there is an
+// error
+type cacheOnce struct {
+	m    sync.Mutex
+	done uint32
+}
+
+// Copied from sync.Once but we don't want to cache the results if there is an
+// error
+func (o *cacheOnce) cache(f func() error) {
+	if atomic.LoadUint32(&o.done) == 1 {
+		return
+	}
+	// Slow-path.
+	o.m.Lock()
+	defer o.m.Unlock()
+	if o.done == 0 {
+		err := f()
+		if err == nil {
+			atomic.StoreUint32(&o.done, 1)
+		}
+	}
+}