1/*
2Copyright 2016 The Kubernetes Authors.
3
4Licensed under the Apache License, Version 2.0 (the "License");
5you may not use this file except in compliance with the License.
6You may obtain a copy of the License at
7
8    http://www.apache.org/licenses/LICENSE-2.0
9
10Unless required by applicable law or agreed to in writing, software
11distributed under the License is distributed on an "AS IS" BASIS,
12WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13See the License for the specific language governing permissions and
14limitations under the License.
15*/
16
17package cache
18
19import (
20	"sync"
21	"time"
22
23	"github.com/hashicorp/golang-lru"
24)
25
26// Clock defines an interface for obtaining the current time
27type Clock interface {
28	Now() time.Time
29}
30
31// realClock implements the Clock interface by calling time.Now()
32type realClock struct{}
33
34func (realClock) Now() time.Time { return time.Now() }
35
36// LRUExpireCache is a cache that ensures the mostly recently accessed keys are returned with
37// a ttl beyond which keys are forcibly expired.
38type LRUExpireCache struct {
39	// clock is used to obtain the current time
40	clock Clock
41
42	cache *lru.Cache
43	lock  sync.Mutex
44}
45
46// NewLRUExpireCache creates an expiring cache with the given size
47func NewLRUExpireCache(maxSize int) *LRUExpireCache {
48	return NewLRUExpireCacheWithClock(maxSize, realClock{})
49}
50
51// NewLRUExpireCacheWithClock creates an expiring cache with the given size, using the specified clock to obtain the current time.
52func NewLRUExpireCacheWithClock(maxSize int, clock Clock) *LRUExpireCache {
53	cache, err := lru.New(maxSize)
54	if err != nil {
55		// if called with an invalid size
56		panic(err)
57	}
58	return &LRUExpireCache{clock: clock, cache: cache}
59}
60
61type cacheEntry struct {
62	value      interface{}
63	expireTime time.Time
64}
65
66// Add adds the value to the cache at key with the specified maximum duration.
67func (c *LRUExpireCache) Add(key interface{}, value interface{}, ttl time.Duration) {
68	c.lock.Lock()
69	defer c.lock.Unlock()
70	c.cache.Add(key, &cacheEntry{value, c.clock.Now().Add(ttl)})
71}
72
73// Get returns the value at the specified key from the cache if it exists and is not
74// expired, or returns false.
75func (c *LRUExpireCache) Get(key interface{}) (interface{}, bool) {
76	c.lock.Lock()
77	defer c.lock.Unlock()
78	e, ok := c.cache.Get(key)
79	if !ok {
80		return nil, false
81	}
82	if c.clock.Now().After(e.(*cacheEntry).expireTime) {
83		c.cache.Remove(key)
84		return nil, false
85	}
86	return e.(*cacheEntry).value, true
87}
88
89// Remove removes the specified key from the cache if it exists
90func (c *LRUExpireCache) Remove(key interface{}) {
91	c.lock.Lock()
92	defer c.lock.Unlock()
93	c.cache.Remove(key)
94}
95
96// Keys returns all the keys in the cache, even if they are expired. Subsequent calls to
97// get may return not found. It returns all keys from oldest to newest.
98func (c *LRUExpireCache) Keys() []interface{} {
99	c.lock.Lock()
100	defer c.lock.Unlock()
101	return c.cache.Keys()
102}
103