Merge pull request #8 from hnlq715/feature/listpool

feat: improve list performance

simplelru/list.go

@@ -0,0 +1,242 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package list implements a doubly linked list.
+//
+// To iterate over a list (where l is a *List):
+//	for e := l.Front(); e != nil; e = e.Next() {
+//		// do something with e.Value
+//	}
+//
+package simplelru
+
+// Element is an element of a linked list.
+type Element struct {
+	// Next and previous pointers in the doubly-linked list of elements.
+	// To simplify the implementation, internally a list l is implemented
+	// as a ring, such that &l.root is both the next element of the last
+	// list element (l.Back()) and the previous element of the first list
+	// element (l.Front()).
+	next, prev *Element
+
+	// The list to which this element belongs.
+	list *List
+
+	// The value stored with this element.
+	Value interface{}
+}
+
+// Next returns the next list element or nil.
+func (e *Element) Next() *Element {
+	if p := e.next; e.list != nil && p != &e.list.root {
+		return p
+	}
+	return nil
+}
+
+// Prev returns the previous list element or nil.
+func (e *Element) Prev() *Element {
+	if p := e.prev; e.list != nil && p != &e.list.root {
+		return p
+	}
+	return nil
+}
+
+// List represents a doubly linked list.
+// The zero value for List is an empty list ready to use.
+type List struct {
+	root Element // sentinel list element, only &root, root.prev, and root.next are used
+	len  int     // current list length excluding (this) sentinel element
+}
+
+// Init initializes or clears list l.
+func (l *List) Init() *List {
+	l.root.next = &l.root
+	l.root.prev = &l.root
+	l.len = 0
+	return l
+}
+
+// New returns an initialized list.
+func New() *List { return new(List).Init() }
+
+// Len returns the number of elements of list l.
+// The complexity is O(1).
+func (l *List) Len() int { return l.len }
+
+// Front returns the first element of list l or nil if the list is empty.
+func (l *List) Front() *Element {
+	if l.len == 0 {
+		return nil
+	}
+	return l.root.next
+}
+
+// Back returns the last element of list l or nil if the list is empty.
+func (l *List) Back() *Element {
+	if l.len == 0 {
+		return nil
+	}
+	return l.root.prev
+}
+
+// lazyInit lazily initializes a zero List value.
+func (l *List) lazyInit() {
+	if l.root.next == nil {
+		l.Init()
+	}
+}
+
+// insert inserts e after at, increments l.len, and returns e.
+func (l *List) insert(e, at *Element) *Element {
+	e.prev = at
+	e.next = at.next
+	e.prev.next = e
+	e.next.prev = e
+	e.list = l
+	l.len++
+	return e
+}
+
+// insertValue is a convenience wrapper for insert(&Element{Value: v}, at).
+func (l *List) insertValue(v interface{}, at *Element) *Element {
+	return l.insert(&Element{Value: v}, at)
+}
+
+// remove removes e from its list, decrements l.len, and returns e.
+func (l *List) remove(e *Element) *Element {
+	e.prev.next = e.next
+	e.next.prev = e.prev
+	e.next = nil // avoid memory leaks
+	e.prev = nil // avoid memory leaks
+	e.list = nil
+	l.len--
+	return e
+}
+
+// move moves e to next to at and returns e.
+func (l *List) move(e, at *Element) *Element {
+	if e == at {
+		return e
+	}
+	e.prev.next = e.next
+	e.next.prev = e.prev
+
+	e.prev = at
+	e.next = at.next
+	e.prev.next = e
+	e.next.prev = e
+
+	return e
+}
+
+// Remove removes e from l if e is an element of list l.
+// It returns the element value e.Value.
+// The element must not be nil.
+func (l *List) Remove(e *Element) interface{} {
+	if e.list == l {
+		// if e.list == l, l must have been initialized when e was inserted
+		// in l or l == nil (e is a zero Element) and l.remove will crash
+		l.remove(e)
+	}
+	return e.Value
+}
+
+// PushFront inserts a new element e with value v at the front of list l and returns e.
+func (l *List) PushFront(v interface{}) *Element {
+	l.lazyInit()
+	return l.insertValue(v, &l.root)
+}
+
+func (l *List) PushElementFront(e *Element) *Element {
+	return l.insert(e, &l.root)
+}
+
+// PushBack inserts a new element e with value v at the back of list l and returns e.
+func (l *List) PushBack(v interface{}) *Element {
+	l.lazyInit()
+	return l.insertValue(v, l.root.prev)
+}
+
+// InsertBefore inserts a new element e with value v immediately before mark and returns e.
+// If mark is not an element of l, the list is not modified.
+// The mark must not be nil.
+func (l *List) InsertBefore(v interface{}, mark *Element) *Element {
+	if mark.list != l {
+		return nil
+	}
+	// see comment in List.Remove about initialization of l
+	return l.insertValue(v, mark.prev)
+}
+
+// InsertAfter inserts a new element e with value v immediately after mark and returns e.
+// If mark is not an element of l, the list is not modified.
+// The mark must not be nil.
+func (l *List) InsertAfter(v interface{}, mark *Element) *Element {
+	if mark.list != l {
+		return nil
+	}
+	// see comment in List.Remove about initialization of l
+	return l.insertValue(v, mark)
+}
+
+// MoveToFront moves element e to the front of list l.
+// If e is not an element of l, the list is not modified.
+// The element must not be nil.
+func (l *List) MoveToFront(e *Element) {
+	if l.root.next == e {
+		return
+	}
+	// see comment in List.Remove about initialization of l
+	l.move(e, &l.root)
+}
+
+// MoveToBack moves element e to the back of list l.
+// If e is not an element of l, the list is not modified.
+// The element must not be nil.
+func (l *List) MoveToBack(e *Element) {
+	if l.root.prev == e {
+		return
+	}
+	// see comment in List.Remove about initialization of l
+	l.move(e, l.root.prev)
+}
+
+// MoveBefore moves element e to its new position before mark.
+// If e or mark is not an element of l, or e == mark, the list is not modified.
+// The element and mark must not be nil.
+func (l *List) MoveBefore(e, mark *Element) {
+	if e == mark {
+		return
+	}
+	l.move(e, mark.prev)
+}
+
+// MoveAfter moves element e to its new position after mark.
+// If e or mark is not an element of l, or e == mark, the list is not modified.
+// The element and mark must not be nil.
+func (l *List) MoveAfter(e, mark *Element) {
+	if e == mark {
+		return
+	}
+	l.move(e, mark)
+}
+
+// PushBackList inserts a copy of another list at the back of list l.
+// The lists l and other may be the same. They must not be nil.
+func (l *List) PushBackList(other *List) {
+	l.lazyInit()
+	for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
+		l.insertValue(e.Value, l.root.prev)
+	}
+}
+
+// PushFrontList inserts a copy of another list at the front of list l.
+// The lists l and other may be the same. They must not be nil.
+func (l *List) PushFrontList(other *List) {
+	l.lazyInit()
+	for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
+		l.insertValue(e.Value, &l.root)
+	}
+}

simplelru/lru.go

@@ -1,7 +1,6 @@
 package simplelru
 
 import (
-	"container/list"
 	"errors"
 	"time"
 )
@@ -12,8 +11,9 @@ type EvictCallback func(key interface{}, value interface{})
 // LRU implements a non-thread safe fixed size LRU cache
 type LRU struct {
 	size      int
-	evictList *list.List
-	items     map[interface{}]*list.Element
+	evictList *List
+	freeList  *List
+	items     map[interface{}]*Element
 	expire    time.Duration
 	onEvict   EvictCallback
 }
@@ -39,11 +39,15 @@ func NewLRU(size int, onEvict EvictCallback) (*LRU, error) {
 	}
 	c := &LRU{
 		size:      size,
-		evictList: list.New(),
-		items:     make(map[interface{}]*list.Element),
+		evictList: New(),
+		freeList:  New(),
+		items:     make(map[interface{}]*Element),
 		expire:    0,
 		onEvict:   onEvict,
 	}
+	for i := 0; i < size; i++ {
+		c.freeList.PushFront(&entry{})
+	}
 	return c, nil
 }
 
@@ -54,11 +58,16 @@ func NewLRUWithExpire(size int, expire time.Duration, onEvict EvictCallback) (*L
 	}
 	c := &LRU{
 		size:      size,
-		evictList: list.New(),
-		items:     make(map[interface{}]*list.Element),
+		evictList: New(),
+		freeList:  New(),
+		items:     make(map[interface{}]*Element),
 		expire:    expire,
 		onEvict:   onEvict,
 	}
+	for i := 0; i < size; i++ {
+		c.freeList.PushFront(&entry{})
+	}
+
 	return c, nil
 }
 
@@ -71,6 +80,10 @@ func (c *LRU) Purge() {
 		delete(c.items, k)
 	}
 	c.evictList.Init()
+	c.freeList.Init()
+	for i := 0; i < c.size; i++ {
+		c.freeList.PushFront(&entry{})
+	}
 }
 
 // Add adds a value to the cache.  Returns true if an eviction occurred.
@@ -96,16 +109,21 @@ func (c *LRU) AddEx(key, value interface{}, expire time.Duration) bool {
 		return false
 	}
 
-	// Add new item
-	ent := &entry{key: key, value: value, expire: ex}
-	entry := c.evictList.PushFront(ent)
-	c.items[key] = entry
-
-	evict := c.evictList.Len() > c.size
+	evict := c.evictList.Len() >= c.size
 	// Verify size not exceeded
 	if evict {
 		c.removeOldest()
 	}
+
+	// Add new item
+	ent := c.freeList.Front()
+	ent.Value.(*entry).key = key
+	ent.Value.(*entry).value = value
+	ent.Value.(*entry).expire = ex
+	c.freeList.Remove(ent)
+	c.evictList.PushElementFront(ent)
+	c.items[key] = ent
+
 	return evict
 }
 
@@ -222,8 +240,9 @@ func (c *LRU) removeOldest() {
 }
 
 // removeElement is used to remove a given list element from the cache
-func (c *LRU) removeElement(e *list.Element) {
+func (c *LRU) removeElement(e *Element) {
 	c.evictList.Remove(e)
+	c.freeList.PushElementFront(e)
 	kv := e.Value.(*entry)
 	delete(c.items, kv.key)
 	if c.onEvict != nil {

simplelru/lru_test.go

@@ -235,3 +235,20 @@ func TestLRU_Resize(t *testing.T) {
 		t.Errorf("Cache should have contained 2 elements")
 	}
 }
+
+func BenchmarkAdd(b *testing.B) {
+	l, _ := NewLRU(1000, nil)
+	b.ResetTimer()
+
+	b.Run("Add with small keys", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			l.Add(i%100, "this is a foo bar")
+		}
+	})
+
+	b.Run("Add with large keys", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			l.Add(i%10000, "this is a foo bar")
+		}
+	})
+}