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| // Copyright (c) 2015 Hans Alexander Gugel <[email protected]> | ||
| // | ||
| // Permission is hereby granted, free of charge, to any person obtaining a copy | ||
| // of this software and associated documentation files (the "Software"), to deal | ||
| // in the Software without restriction, including without limitation the rights | ||
| // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | ||
| // copies of the Software, and to permit persons to whom the Software is | ||
| // furnished to do so, subject to the following conditions: | ||
| // | ||
| // The above copyright notice and this permission notice shall be included in all | ||
| // copies or substantial portions of the Software. | ||
| // | ||
| // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | ||
| // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | ||
| // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | ||
| // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | ||
| // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | ||
| // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | ||
| // SOFTWARE. | ||
|
|
||
| // This file contains a modified version of package arc from | ||
| // https://github.com/alexanderGugel/arc | ||
| // | ||
| // It implements the ARC (Adaptive Replacement Cache) algorithm as detailed in | ||
| // https://www.usenix.org/legacy/event/fast03/tech/full_papers/megiddo/megiddo.pdf | ||
|
|
||
| package trie | ||
|
|
||
| import ( | ||
| "container/list" | ||
| "sync" | ||
| ) | ||
|
|
||
| type arc struct { | ||
| p int | ||
| c int | ||
| t1 *list.List | ||
| b1 *list.List | ||
| t2 *list.List | ||
| b2 *list.List | ||
| cache map[string]*entry | ||
| mutex sync.Mutex | ||
| } | ||
|
|
||
| type entry struct { | ||
| key hashNode | ||
| value node | ||
| ll *list.List | ||
| el *list.Element | ||
| } | ||
|
|
||
| // newARC returns a new Adaptive Replacement Cache with the | ||
| // given capacity. | ||
| func newARC(c int) *arc { | ||
| return &arc{ | ||
| c: c, | ||
| t1: list.New(), | ||
| b1: list.New(), | ||
| t2: list.New(), | ||
| b2: list.New(), | ||
| cache: make(map[string]*entry, c), | ||
| } | ||
| } | ||
|
|
||
| // Put inserts a new key-value pair into the cache. | ||
| // This optimizes future access to this entry (side effect). | ||
| func (a *arc) Put(key hashNode, value node) bool { | ||
| a.mutex.Lock() | ||
| defer a.mutex.Unlock() | ||
| ent, ok := a.cache[string(key)] | ||
| if ok != true { | ||
| ent = &entry{key: key, value: value} | ||
| a.req(ent) | ||
| a.cache[string(key)] = ent | ||
| } else { | ||
| ent.value = value | ||
| a.req(ent) | ||
| } | ||
| return ok | ||
| } | ||
|
|
||
| // Get retrieves a previously via Set inserted entry. | ||
| // This optimizes future access to this entry (side effect). | ||
| func (a *arc) Get(key hashNode) (value node, ok bool) { | ||
| a.mutex.Lock() | ||
| defer a.mutex.Unlock() | ||
| ent, ok := a.cache[string(key)] | ||
| if ok { | ||
| a.req(ent) | ||
| return ent.value, ent.value != nil | ||
| } | ||
| return nil, false | ||
| } | ||
|
|
||
| func (a *arc) req(ent *entry) { | ||
| if ent.ll == a.t1 || ent.ll == a.t2 { | ||
| // Case I | ||
| ent.setMRU(a.t2) | ||
| } else if ent.ll == a.b1 { | ||
| // Case II | ||
| // Cache Miss in t1 and t2 | ||
|
|
||
| // Adaptation | ||
| var d int | ||
| if a.b1.Len() >= a.b2.Len() { | ||
| d = 1 | ||
| } else { | ||
| d = a.b2.Len() / a.b1.Len() | ||
| } | ||
| a.p = a.p + d | ||
| if a.p > a.c { | ||
| a.p = a.c | ||
| } | ||
|
|
||
| a.replace(ent) | ||
| ent.setMRU(a.t2) | ||
| } else if ent.ll == a.b2 { | ||
| // Case III | ||
| // Cache Miss in t1 and t2 | ||
|
|
||
| // Adaptation | ||
| var d int | ||
| if a.b2.Len() >= a.b1.Len() { | ||
| d = 1 | ||
| } else { | ||
| d = a.b1.Len() / a.b2.Len() | ||
| } | ||
| a.p = a.p - d | ||
| if a.p < 0 { | ||
| a.p = 0 | ||
| } | ||
|
|
||
| a.replace(ent) | ||
| ent.setMRU(a.t2) | ||
| } else if ent.ll == nil { | ||
| // Case IV | ||
|
|
||
| if a.t1.Len()+a.b1.Len() == a.c { | ||
| // Case A | ||
| if a.t1.Len() < a.c { | ||
| a.delLRU(a.b1) | ||
| a.replace(ent) | ||
| } else { | ||
| a.delLRU(a.t1) | ||
| } | ||
| } else if a.t1.Len()+a.b1.Len() < a.c { | ||
| // Case B | ||
| if a.t1.Len()+a.t2.Len()+a.b1.Len()+a.b2.Len() >= a.c { | ||
| if a.t1.Len()+a.t2.Len()+a.b1.Len()+a.b2.Len() == 2*a.c { | ||
| a.delLRU(a.b2) | ||
| } | ||
| a.replace(ent) | ||
| } | ||
| } | ||
|
|
||
| ent.setMRU(a.t1) | ||
| } | ||
| } | ||
|
|
||
| func (a *arc) delLRU(list *list.List) { | ||
| lru := list.Back() | ||
| list.Remove(lru) | ||
| delete(a.cache, string(lru.Value.(*entry).key)) | ||
| } | ||
|
|
||
| func (a *arc) replace(ent *entry) { | ||
| if a.t1.Len() > 0 && ((a.t1.Len() > a.p) || (ent.ll == a.b2 && a.t1.Len() == a.p)) { | ||
| lru := a.t1.Back().Value.(*entry) | ||
| lru.value = nil | ||
| lru.setMRU(a.b1) | ||
| } else { | ||
| lru := a.t2.Back().Value.(*entry) | ||
| lru.value = nil | ||
| lru.setMRU(a.b2) | ||
| } | ||
| } | ||
|
|
||
| func (e *entry) setLRU(list *list.List) { | ||
| e.detach() | ||
| e.ll = list | ||
| e.el = e.ll.PushBack(e) | ||
| } | ||
|
|
||
| func (e *entry) setMRU(list *list.List) { | ||
| e.detach() | ||
| e.ll = list | ||
| e.el = e.ll.PushFront(e) | ||
| } | ||
|
|
||
| func (e *entry) detach() { | ||
| if e.ll != nil { | ||
| e.ll.Remove(e.el) | ||
| } | ||
| } |
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