Frederick F. Kautz IV
10 years ago
parent
fdf860e8eb
commit
af273c5d0f
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/* |
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Copyright 2013 Google Inc. |
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Licensed under the Apache License, Version 2.0 (the "License"); |
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you may not use this file except in compliance with the License. |
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You may obtain a copy of the License at |
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software |
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distributed under the License is distributed on an "AS IS" BASIS, |
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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See the License for the specific language governing permissions and |
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limitations under the License. |
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*/ |
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// Package lru implements an LRU cache.
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package lru |
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import "container/list" |
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// Cache is an LRU cache. It is not safe for concurrent access.
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type Cache struct { |
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// MaxEntries is the maximum number of cache entries before
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// an item is evicted. Zero means no limit.
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MaxEntries int |
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// OnEvicted optionally specificies a callback function to be
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// executed when an entry is purged from the cache.
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OnEvicted func(key Key, value interface{}) |
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ll *list.List |
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cache map[interface{}]*list.Element |
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} |
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// A Key may be any value that is comparable. See http://golang.org/ref/spec#Comparison_operators
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type Key interface{} |
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type entry struct { |
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key Key |
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value interface{} |
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} |
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// New creates a new Cache.
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// If maxEntries is zero, the cache has no limit and it's assumed
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// that eviction is done by the caller.
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func New(maxEntries int) *Cache { |
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return &Cache{ |
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MaxEntries: maxEntries, |
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ll: list.New(), |
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cache: make(map[interface{}]*list.Element), |
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} |
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} |
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// Add adds a value to the cache.
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func (c *Cache) Add(key Key, value interface{}) { |
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if c.cache == nil { |
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c.cache = make(map[interface{}]*list.Element) |
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c.ll = list.New() |
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} |
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if ee, ok := c.cache[key]; ok { |
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c.ll.MoveToFront(ee) |
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ee.Value.(*entry).value = value |
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return |
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} |
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ele := c.ll.PushFront(&entry{key, value}) |
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c.cache[key] = ele |
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if c.MaxEntries != 0 && c.ll.Len() > c.MaxEntries { |
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c.RemoveOldest() |
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} |
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} |
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// Get looks up a key's value from the cache.
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func (c *Cache) Get(key Key) (value interface{}, ok bool) { |
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if c.cache == nil { |
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return |
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} |
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if ele, hit := c.cache[key]; hit { |
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c.ll.MoveToFront(ele) |
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return ele.Value.(*entry).value, true |
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} |
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return |
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} |
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// Remove removes the provided key from the cache.
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func (c *Cache) Remove(key Key) { |
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if c.cache == nil { |
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return |
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} |
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if ele, hit := c.cache[key]; hit { |
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c.removeElement(ele) |
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} |
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} |
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// RemoveOldest removes the oldest item from the cache.
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func (c *Cache) RemoveOldest() { |
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if c.cache == nil { |
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return |
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} |
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ele := c.ll.Back() |
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if ele != nil { |
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c.removeElement(ele) |
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} |
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} |
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func (c *Cache) removeElement(e *list.Element) { |
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c.ll.Remove(e) |
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kv := e.Value.(*entry) |
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delete(c.cache, kv.key) |
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if c.OnEvicted != nil { |
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c.OnEvicted(kv.key, kv.value) |
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} |
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} |
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// Len returns the number of items in the cache.
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func (c *Cache) Len() int { |
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if c.cache == nil { |
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return 0 |
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} |
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return c.ll.Len() |
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} |
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@ -1,73 +0,0 @@ |
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/* |
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Copyright 2013 Google Inc. |
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Licensed under the Apache License, Version 2.0 (the "License"); |
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you may not use this file except in compliance with the License. |
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You may obtain a copy of the License at |
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software |
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distributed under the License is distributed on an "AS IS" BASIS, |
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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See the License for the specific language governing permissions and |
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limitations under the License. |
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*/ |
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package lru |
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import ( |
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"testing" |
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) |
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type simpleStruct struct { |
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int |
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string |
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} |
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type complexStruct struct { |
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int |
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simpleStruct |
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} |
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var getTests = []struct { |
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name string |
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keyToAdd interface{} |
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keyToGet interface{} |
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expectedOk bool |
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}{ |
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{"string_hit", "myKey", "myKey", true}, |
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{"string_miss", "myKey", "nonsense", false}, |
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{"simple_struct_hit", simpleStruct{1, "two"}, simpleStruct{1, "two"}, true}, |
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{"simeple_struct_miss", simpleStruct{1, "two"}, simpleStruct{0, "noway"}, false}, |
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{"complex_struct_hit", complexStruct{1, simpleStruct{2, "three"}}, |
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complexStruct{1, simpleStruct{2, "three"}}, true}, |
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} |
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func TestGet(t *testing.T) { |
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for _, tt := range getTests { |
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lru := New(0) |
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lru.Add(tt.keyToAdd, 1234) |
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val, ok := lru.Get(tt.keyToGet) |
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if ok != tt.expectedOk { |
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t.Fatalf("%s: cache hit = %v; want %v", tt.name, ok, !ok) |
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} else if ok && val != 1234 { |
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t.Fatalf("%s expected get to return 1234 but got %v", tt.name, val) |
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} |
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} |
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} |
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func TestRemove(t *testing.T) { |
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lru := New(0) |
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lru.Add("myKey", 1234) |
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if val, ok := lru.Get("myKey"); !ok { |
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t.Fatal("TestRemove returned no match") |
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} else if val != 1234 { |
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t.Fatalf("TestRemove failed. Expected %d, got %v", 1234, val) |
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} |
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lru.Remove("myKey") |
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if _, ok := lru.Get("myKey"); ok { |
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t.Fatal("TestRemove returned a removed entry") |
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} |
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} |
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