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queue.go
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queue.go
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// Copyright 2019 PayPal Inc.
//
// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package lib
// Queue is interface for a queue implementation
type Queue interface {
// Len function tells how many elements are
Len() int
// Push adds an element to the queue, at the end
Push(el interface{}) bool
// PushFront adds an element to the queue, at the front - basically making this a stack
PushFront(el interface{}) bool
// Poll poss an element from the queue
Poll() interface{}
// Remove removes the element having the given value
Remove(el interface{}) bool
// ForEachRemove walks the entire list removeing elements satisfying the condition
ForEachRemove(f func (interface{}) bool) int
}
// ringQueue implements Queue using internally a ring buffer.
// Note: this queue has disting elements, iot doesn't allow adding a duplicate entry
type ringQueue struct {
data []interface{}
head, tail, capacity int
// idmap helps to eficiently check if an element is in the list, so that Push/PushFront will not add a duplicate
idmap map[interface{}]bool
}
// NewQueue creates a queue
func NewQueue() Queue {
capacity := 128
return &ringQueue{data: make([]interface{}, capacity), capacity: capacity, idmap: make(map[interface{}]bool)}
}
// Len function tells how many elements are
func (q *ringQueue)Len() int {
if q.tail >= q.head {
return q.tail - q.head
}
return q.tail - q.head + q.capacity
}
func (q *ringQueue)double() {
data := q.data
capacity := q.capacity
q.capacity *= 2
q.data = make([]interface{}, q.capacity)
idxs := q.head
idxd := 0
for idxs != q.tail {
q.data[idxd] = data[idxs]
idxd = idxd + 1
idxs = (idxs + 1) % capacity
}
q.head = 0
q.tail = idxd
}
// Push adds an element to the queue, at the end
func (q *ringQueue)Push(el interface{}) bool {
if q.idmap[el] {
return false
}
q.idmap[el] = true
if q.Len() + 1 == q.capacity {
q.double()
}
q.data[q.tail] = el
q.tail = q.incr(q.tail)
return true
}
// PushFront adds an element to the queue, at the front - basically making this a stack
func (q *ringQueue)PushFront(el interface{}) bool{
if q.idmap[el] {
return false
}
q.idmap[el] = true
if q.Len() + 1 == q.capacity {
q.double()
}
q.head = q.decr(q.head)
q.data[q.head] = el
return true
}
// Poll poss an element from the queue
func (q *ringQueue)Poll() interface{} {
if q.Len() == 0 {
return nil
}
el := q.data[q.head]
q.head = q.incr(q.head)
delete(q.idmap, el)
return el
}
func (q *ringQueue)decr(pos int) int{
return ((pos + q.capacity - 1) % q.capacity)
}
func (q *ringQueue)incr(pos int) int{
return ((pos + 1) % q.capacity)
}
func (q *ringQueue)remove(pos int) {
delete(q.idmap, q.data[pos])
next := q.incr(pos)
for next != q.tail {
q.data[pos] = q.data[next]
pos = next
next = q.incr(next)
}
q.tail = q.decr(q.tail)
}
// Remove removes the element having the given value
func (q *ringQueue)Remove(el interface{}) bool {
pos := q.head
for pos != q.tail {
if el == q.data[pos] {
q.remove(pos)
return true
}
pos = q.incr(pos)
}
return false
}
// ForEachRemove walks the entire list removeing elements satisfying the condition
func (q *ringQueue)ForEachRemove(f func (interface{}) bool) int {
cnt := 0
pos := q.head
for pos != q.tail {
if f(q.data[pos]) {
q.remove(pos)
cnt++
} else {
pos = q.incr(pos)
}
}
return cnt
}