js控制并发请求

一. 设计思路

功能：目的在有限的并发池中运行多个 promise 返回和异步函数。

1. 添加异步任务
2. 执行异步任务
3. 限制最大并发数量

二.实现

interface Fn {(): Promise<any>
}
export default class Pipeline {private list: { // 请求队列fn: Fn,resolve: (value: any) => voidreject: (err: any) => void}[]private count = 0 // 当前并发数量private max = 0 // 最大并发数量constructor (max: number) {this.max = maxthis.count = 0this.list = []}// 添加请求任务add (fn:Fn) {return new Promise((resolve, reject) => {this.list.push({fn,resolve,reject})this.run()})}// 执行任务run () {// 如果当前并发数小于最大并发数量if(this.count < this.max && this.list.length ) {const { fn, resolve, reject } = this.list.shift()!if(fn) {// 每执行一个，当前并发+1this.count++fn().then((res) => {resolve(res)}).catch(err => {reject(err)}).finally (() => {// 每完成一个请求this.count--this.run()}) }}}
}

三. 使用

import Pipeline from "./pipeline"
interface Fn {() : Promise<any>
}
// 创建50个请求
function createRequest () {const arr: Fn[] = []for(let i=0; i < 50; i++) {arr.push(() => new Promise((resolve, reject) => {setTimeout(() => {resolve(i)}, 2 * 2000)})) }return arr
}export async function request() {const pipeline = new Pipeline(1)const arr = createRequest()// 并发执行所有请求const promises = arr.map((fn, index) => {console.log("i", `第${index}个请求`)return pipeline.add(fn).then(res => {console.log("请求结果", res)return res})})// 等待所有请求完成await Promise.all(promises)}