core, trie: new trie
This commit is contained in:
Felix Lange
194
trie/arc.go
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194
trie/arc.go
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// Copyright (c) 2015 Hans Alexander Gugel <alexander.gugel@gmail.com>
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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// This file contains a modified version of package arc from
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// https://github.com/alexanderGugel/arc
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//
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// It implements the ARC (Adaptive Replacement Cache) algorithm as detailed in
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// https://www.usenix.org/legacy/event/fast03/tech/full_papers/megiddo/megiddo.pdf
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package trie
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import (
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"container/list"
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"sync"
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)
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type arc struct {
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p int
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c int
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t1 *list.List
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b1 *list.List
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t2 *list.List
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b2 *list.List
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cache map[string]*entry
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mutex sync.Mutex
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}
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type entry struct {
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key hashNode
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value node
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ll *list.List
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el *list.Element
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}
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// newARC returns a new Adaptive Replacement Cache with the
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// given capacity.
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func newARC(c int) *arc {
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return &arc{
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c: c,
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t1: list.New(),
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b1: list.New(),
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t2: list.New(),
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b2: list.New(),
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cache: make(map[string]*entry, c),
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}
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}
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// Put inserts a new key-value pair into the cache.
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// This optimizes future access to this entry (side effect).
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func (a *arc) Put(key hashNode, value node) bool {
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a.mutex.Lock()
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defer a.mutex.Unlock()
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ent, ok := a.cache[string(key)]
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if ok != true {
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ent = &entry{key: key, value: value}
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a.req(ent)
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a.cache[string(key)] = ent
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} else {
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ent.value = value
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a.req(ent)
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}
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return ok
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}
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// Get retrieves a previously via Set inserted entry.
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// This optimizes future access to this entry (side effect).
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func (a *arc) Get(key hashNode) (value node, ok bool) {
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a.mutex.Lock()
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defer a.mutex.Unlock()
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ent, ok := a.cache[string(key)]
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if ok {
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a.req(ent)
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return ent.value, ent.value != nil
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}
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return nil, false
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}
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func (a *arc) req(ent *entry) {
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if ent.ll == a.t1 || ent.ll == a.t2 {
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// Case I
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ent.setMRU(a.t2)
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} else if ent.ll == a.b1 {
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// Case II
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// Cache Miss in t1 and t2
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// Adaptation
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var d int
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if a.b1.Len() >= a.b2.Len() {
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d = 1
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} else {
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d = a.b2.Len() / a.b1.Len()
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}
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a.p = a.p + d
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if a.p > a.c {
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a.p = a.c
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}
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a.replace(ent)
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ent.setMRU(a.t2)
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} else if ent.ll == a.b2 {
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// Case III
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// Cache Miss in t1 and t2
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// Adaptation
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var d int
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if a.b2.Len() >= a.b1.Len() {
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d = 1
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} else {
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d = a.b1.Len() / a.b2.Len()
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}
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a.p = a.p - d
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if a.p < 0 {
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a.p = 0
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}
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a.replace(ent)
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ent.setMRU(a.t2)
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} else if ent.ll == nil {
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// Case IV
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if a.t1.Len()+a.b1.Len() == a.c {
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// Case A
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if a.t1.Len() < a.c {
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a.delLRU(a.b1)
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a.replace(ent)
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} else {
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a.delLRU(a.t1)
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}
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} else if a.t1.Len()+a.b1.Len() < a.c {
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// Case B
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if a.t1.Len()+a.t2.Len()+a.b1.Len()+a.b2.Len() >= a.c {
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if a.t1.Len()+a.t2.Len()+a.b1.Len()+a.b2.Len() == 2*a.c {
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a.delLRU(a.b2)
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}
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a.replace(ent)
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}
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}
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ent.setMRU(a.t1)
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}
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}
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func (a *arc) delLRU(list *list.List) {
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lru := list.Back()
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list.Remove(lru)
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delete(a.cache, string(lru.Value.(*entry).key))
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}
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func (a *arc) replace(ent *entry) {
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if a.t1.Len() > 0 && ((a.t1.Len() > a.p) || (ent.ll == a.b2 && a.t1.Len() == a.p)) {
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lru := a.t1.Back().Value.(*entry)
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lru.value = nil
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lru.setMRU(a.b1)
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} else {
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lru := a.t2.Back().Value.(*entry)
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lru.value = nil
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lru.setMRU(a.b2)
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}
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}
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func (e *entry) setLRU(list *list.List) {
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e.detach()
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e.ll = list
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e.el = e.ll.PushBack(e)
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}
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func (e *entry) setMRU(list *list.List) {
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e.detach()
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e.ll = list
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e.el = e.ll.PushFront(e)
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}
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func (e *entry) detach() {
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if e.ll != nil {
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e.ll.Remove(e.el)
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}
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}
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