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queue.go
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queue.go
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package concurrentcache
import (
"errors"
"sync"
)
// Queue struct
type Queue struct {
head *QNode
tail *QNode
pool *sync.Pool
}
// QNode struct
type QNode struct {
prev *QNode
next *QNode
V interface{}
}
// NewQueue return a Queue
func NewQueue() *Queue {
pool := &sync.Pool{
New: func() interface{} {
return &QNode{}
},
}
return &Queue{pool: pool}
}
// NewQNode return a QNode
func (q *Queue) NewQNode(v interface{}) *QNode {
n := q.pool.Get().(*QNode)
n.reset()
n.V = v
return n
}
// Recycle reuse QNode
func (q *Queue) Recycle(n *QNode) {
if n != nil {
q.pool.Put(n)
}
}
func (n *QNode) reset() {
if n != nil {
n.prev = nil
n.next = nil
n.V = nil
}
}
// LPush a QNode to the left of the Queue
func (q *Queue) LPush(n *QNode) {
q.push(n, true)
}
// RPush a QNode to the right of the Queue
func (q *Queue) RPush(n *QNode) {
q.push(n, false)
}
func (q *Queue) push(n *QNode, left bool) {
if q.Empty() {
n.next, n.prev = nil, nil
q.head, q.tail = n, n
return
}
if left {
n.next, n.prev = q.head, nil
q.head.prev = n
q.head = n
} else {
n.next, n.prev = nil, q.tail
q.tail.next = n
q.tail = n
}
}
// InsertAfter prev QNode
func (q *Queue) InsertAfter(prev, n *QNode) (bool, error) {
if prev == nil || n == nil {
return false, errors.New("invalid node")
}
n.prev = prev
n.next = prev.next
if prev.next != nil {
prev.next.prev = n
}
prev.next = n
if prev == q.tail {
q.tail = n
}
return true, nil
}
// InsertBefore next QNode
func (q *Queue) InsertBefore(next, n *QNode) (bool, error) {
if next == nil || n == nil {
return false, errors.New("invalid node")
}
n.next = next
n.prev = next.prev
if next.prev != nil {
next.prev.next = n
}
next.prev = n
if next == q.head {
q.head = n
}
return true, nil
}
// LPop QNode from the left of Queue
func (q *Queue) LPop() *QNode {
return q.pop(true)
}
// RPop QNode from the right of Queue
func (q *Queue) RPop() *QNode {
return q.pop(false)
}
func (q *Queue) pop(left bool) *QNode {
if q.Empty() {
return nil
}
if left {
n := q.head
if q.head == q.tail {
q.head, q.tail = nil, nil
} else {
q.head = q.head.next
}
n.next, n.prev = nil, nil
return n
}
n := q.tail
if q.head == q.tail {
q.head, q.tail = nil, nil
} else {
q.tail = q.tail.prev
}
n.next, n.prev = nil, nil
return n
}
// Delete a QNode
func (q *Queue) Delete(n *QNode) (bool, error) {
if n == nil {
return false, errors.New("invalid node")
}
if n.prev != nil {
n.prev.next = n.next
} else if n == q.head && n != nil {
q.head = n.next
}
if n.next != nil {
n.next.prev = n.prev
} else if n == q.tail && n != nil {
q.tail = n.prev
}
n.prev = nil
n.next = nil
return true, nil
}
// Empty if Queue is empty
func (q *Queue) Empty() bool {
if q.head == q.tail && q.head == nil {
return true
}
return false
}