object_cache.go

Documentation: k8s.io/kubernetes/pkg/kubelet/util/cache

     1  /*
     2  Copyright 2016 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 cache
    18  
    19  import (
    20  	"time"
    21  
    22  	expirationcache "k8s.io/client-go/tools/cache"
    23  )
    24  
    25  // ObjectCache is a simple wrapper of expiration cache that
    26  // 1. use string type key
    27  // 2. has an updater to get value directly if it is expired
    28  // 3. then update the cache
    29  type ObjectCache struct {
    30  	cache   expirationcache.Store
    31  	updater func() (interface{}, error)
    32  }
    33  
    34  // objectEntry is an object with string type key.
    35  type objectEntry struct {
    36  	key string
    37  	obj interface{}
    38  }
    39  
    40  // NewObjectCache creates ObjectCache with an updater.
    41  // updater returns an object to cache.
    42  func NewObjectCache(f func() (interface{}, error), ttl time.Duration) *ObjectCache {
    43  	return &ObjectCache{
    44  		updater: f,
    45  		cache:   expirationcache.NewTTLStore(stringKeyFunc, ttl),
    46  	}
    47  }
    48  
    49  // stringKeyFunc is a string as cache key function
    50  func stringKeyFunc(obj interface{}) (string, error) {
    51  	key := obj.(objectEntry).key
    52  	return key, nil
    53  }
    54  
    55  // Get gets cached objectEntry by using a unique string as the key.
    56  func (c *ObjectCache) Get(key string) (interface{}, error) {
    57  	value, ok, err := c.cache.Get(objectEntry{key: key})
    58  	if err != nil {
    59  		return nil, err
    60  	}
    61  	if !ok {
    62  		obj, err := c.updater()
    63  		if err != nil {
    64  			return nil, err
    65  		}
    66  		err = c.cache.Add(objectEntry{
    67  			key: key,
    68  			obj: obj,
    69  		})
    70  		if err != nil {
    71  			return nil, err
    72  		}
    73  		return obj, nil
    74  	}
    75  	return value.(objectEntry).obj, nil
    76  }
    77  
    78  // Add adds objectEntry by using a unique string as the key.
    79  func (c *ObjectCache) Add(key string, obj interface{}) error {
    80  	return c.cache.Add(objectEntry{key: key, obj: obj})
    81  }
    82
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