'use strict';
const {  Array,} = primordials;
// Currently optimal queue size, tested on V8 6.0 - 6.6. Must be power of two.const kSize = 2048;const kMask = kSize - 1;


const FixedCircularBuffer = class FixedCircularBuffer {  constructor() {    this.bottom = 0;    this.top = 0;    this.list = new Array(kSize);    this.next = null;  }
  isEmpty() {    return this.top === this.bottom;  }  // 要判断回环  isFull() {    return ((this.top + 1) & kMask) === this.bottom;  }
  push(data) {    this.list[this.top] = data;    this.top = (this.top + 1) & kMask;  }  // 移除一个元素，更新位置  shift() {    const nextItem = this.list[this.bottom];    // 没有元素了，不需要更新位置    if (nextItem === undefined)      return null;    this.list[this.bottom] = undefined;    this.bottom = (this.bottom + 1) & kMask;    return nextItem;  }};
module.exports = class FixedQueue {  constructor() {    this.head = this.tail = new FixedCircularBuffer();  }
  isEmpty() {    return this.head.isEmpty();  }
  push(data) {    // 满了则申请一个新的，head指向新的，tail指向最开始的那个，即最旧的    if (this.head.isFull()) {      // Head is full: Creates a new queue, sets the old queue's `.next` to it,      // and sets it as the new main queue.      this.head = this.head.next = new FixedCircularBuffer();    }    this.head.push(data);  }
  shift() {    const tail = this.tail;    const next = tail.shift();    // 消费完一个FixedCircularBuffer了，下一个    if (tail.isEmpty() && tail.next !== null) {      // If there is another queue, it forms the new tail.      this.tail = tail.next;    }    return next;  }};