metrics_cached.go

Documentation: k8s.io/kubernetes/pkg/volume

     1  /*
     2  Copyright 2014 The Kubernetes Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package volume
    18  
    19  import (
    20  	"sync"
    21  	"sync/atomic"
    22  )
    23  
    24  var _ MetricsProvider = &cachedMetrics{}
    25  
    26  // cachedMetrics represents a MetricsProvider that wraps another provider and
    27  // caches the result.
    28  type cachedMetrics struct {
    29  	wrapped       MetricsProvider
    30  	resultError   error
    31  	resultMetrics *Metrics
    32  	once          cacheOnce
    33  }
    34  
    35  // NewCachedMetrics creates a new cachedMetrics wrapping another
    36  // MetricsProvider and caching the results.
    37  func NewCachedMetrics(provider MetricsProvider) MetricsProvider {
    38  	return &cachedMetrics{wrapped: provider}
    39  }
    40  
    41  // GetMetrics runs the wrapped metrics provider's GetMetrics method once and
    42  // caches the result. Will not cache result if there is an error.
    43  // See MetricsProvider.GetMetrics
    44  func (md *cachedMetrics) GetMetrics() (*Metrics, error) {
    45  	md.once.cache(func() error {
    46  		md.resultMetrics, md.resultError = md.wrapped.GetMetrics()
    47  		return md.resultError
    48  	})
    49  	return md.resultMetrics, md.resultError
    50  }
    51  
    52  // Copied from sync.Once but we don't want to cache the results if there is an
    53  // error
    54  type cacheOnce struct {
    55  	m    sync.Mutex
    56  	done uint32
    57  }
    58  
    59  // Copied from sync.Once but we don't want to cache the results if there is an
    60  // error
    61  func (o *cacheOnce) cache(f func() error) {
    62  	if atomic.LoadUint32(&o.done) == 1 {
    63  		return
    64  	}
    65  	// Slow-path.
    66  	o.m.Lock()
    67  	defer o.m.Unlock()
    68  	if o.done == 0 {
    69  		err := f()
    70  		if err == nil {
    71  			atomic.StoreUint32(&o.done, 1)
    72  		}
    73  	}
    74  }
    75
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