core, trie: new trie

1 files changed, 194 insertions, 0 deletions

diff --git a/trie/arc.go b/trie/arc.go
new file mode 100644
index 000000000..9da012e16
--- /dev/null
+++ b/trie/arc.go
@@ -0,0 +1,194 @@
+// Copyright (c) 2015 Hans Alexander Gugel <alexander.gugel@gmail.com>
+//
+// 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)
+	}
+}