geotile_sdk/src/regionCache.js

A tile sdk for Cloud Optimised Geotiff and shapefile

/*
 * @Description:  将当前瓦片请求的纵向相关区域加入slowList(慢队列), 空闲时(无瓦片请求时)加入orderList, 获取瓦片
 * @Author: luojun1
 * @Date: 2021-10-21 17:25:12
 * @LastEditTime: 2021-12-14 15:35:49
 */

// 缓存大小
var capability = 200 // 默认缓存大小,缓存大小为100时,大约占用74.8MB内存

// 双向链表, 存放paddingRegion, 为了实现定期淘汰无用瓦片,对paddingRegion进行排序(不存放order而是存放paddingRegion)
// 记录添加的顺序, 将后添加和最近访问的paddingRegion排在前面,定期删除链表尾部的paddingRegion
class RegionNode {
  constructor (paddingRegion, z, xmlUUID) {
    this.pre = null
    this.next = null
    this.Region = paddingRegion
    this.z = z
    this.xmlUUID = xmlUUID
  }
}

class LinkedList {
  constructor (size) {
    this.capability = size || capability // 默认缓存大小,缓存大小为100时,大约占用74.8MB内存
    this.length = 0
    this.head = null
    this.tail = null
  }
  addNode (cur) {
    if (!cur) {
      console.log('addNode:null')
      return
    }
    cur.next = this.head
    if (this.head !== null) {
      this.head.pre = cur
    }
    this.head = cur // 更新head
    if (!this.tail) {
      this.tail = this.head
    }
    this.length++
  }
  rmNode (cur) {
    if (!cur) {
      console.log('rmNode:null')
      return
    }
    if (cur === this.head && cur === this.tail) {
      this.head = null
      this.tail = null
    } else if (cur === this.tail) {
      this.tail = cur.pre
      cur.pre.next = null
    } else if (cur === this.head) {
      this.head = cur.next
      cur.next.pre = null
    } else {
      cur.pre.next = cur.next
      cur.next.pre = cur.pre
    }
    this.length--
    return cur
  }
}

/** ******** 事件驱动的地图瓦片区域缓存************/
/** hashmap + 双向链表 作为瓦片区域缓存的基础结构 */
var regionCache = new LinkedList()

function addRegion (paddingRegion, z, xmlUUID) {
  var cur = new RegionNode(paddingRegion, z, xmlUUID)
  regionCache.addNode(cur)
  return cur
}
// 将最近访问过的region排到链表前
function updateRegion (Node) {
  // console.log('updateRegion:')
  regionCache.rmNode(Node)
  regionCache.addNode(Node)
}
function rmRegion (Node) {
  regionCache.rmNode(Node)
}
// 检查缓存利用率
function checkRegionCache (cancelOrders) {
  // console.log('regionCache.#length:', regionCache.length)
  // var curNode = regionCache.head
  // while (curNode) {
  //   console.log('paddingRegion:', curNode)
  //   curNode = curNode.next
  // }
  while (regionCache.length >= regionCache.capability) {
    cancelOrders(regionCache.tail.Region, regionCache.tail.z, regionCache.tail.xmlUUID)
    regionCache.rmNode(regionCache.tail)
  }
}

// 慢队列(stack)， 存放瓦片请求的纵向相关区域， 空闲时加入orderList请求瓦片
var slowList = []

// 预加载队列的容量，如队列满载，则删除旧的region
// 0.8是低级别region占所有region缓存的比例，当前级别region：3×4×图层数量，低级别region：3×2×4×2×图层数，当前级别：低级别=1：4
var slowListCap = capability * 0.8

class Region {
  constructor (lowLevelRegion, z, xmlUUID) {
    this.Region = lowLevelRegion
    this.z = z
    this.xmlUUID = xmlUUID
  }
}

function addVerticalRegion (region, z, xmlUUID) {
  slowList.push(new Region(region, z, xmlUUID))
  while (slowList.length >= slowListCap) {
    slowList.shift()
  }
  console.log('slowList.length:', slowList.length)
}

function preloadVerticalRegion (recall) {
  var region = slowList.pop()
  if (region) {
    recall(region.Region, region.z, region.xmlUUID)
    return null
  } else {
    return new Error('slowList is empty！！')
  }
}

module.exports = {
  addRegion,
  updateRegion,
  rmRegion,
  checkRegionCache,
  addVerticalRegion,
  preloadVerticalRegion
}