| /* |
| 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) |
| } |
| } |
| } |