原生promise、async怎么实现控制并发数量
发布于 2 年前 作者 zhang14725804 6198 次浏览 来自 问答

look,是原生,不是类库

18 回复

用 for 遍历,然后一次拿2个,或者多个出来 再 Promise.all 之后 再 await 呗。

你就按照并发数量数量push到数组里面 用await Promise.all

同意楼上的观点,建议楼主去看看bluebird中Promise.map源码,bluebird可以做到控制并发数量。

来自酷炫的 CNodeMD

await Promise.all([…]);

@Bingmang 好,我看看

@zhang962976642 能不能贴个代码,小白表示蒙蔽

@Sunshine168 能不能贴个代码,小白表示蒙蔽

@MiYogurt 能不能贴个代码,小白表示蒙蔽

var cheerio = require(“cheerio”); var superagent = require(“superagent”); var fs = require(‘fs’); const charset = require(‘superagent-charset’); charset(superagent);

var pages = []; var basicUrl = ‘http://www.u148.net/list/

async function fetch() { for (let i = 1; i < 1318; i++) { await SpiderPage(basicUrl + i); } }

async function SpiderPage(urllll) { console.log(“urllll::” + urllll) return new Promise((resolve, reject) => { superagent.get(urllll) .charset(‘utf8’) .end(function(err, sres) { if (err) { return next(err); } mkdir(sres)

		});
	resolve();
})

}

function mkdir(sres) { var $ = cheerio.load(sres.text); var eachUrl; var eachTitle; var eachWriter; var eachSummary; var eachData; var eachLook; var singleContext = [];

$('.list-content').each(function() {
	eachUrl = 'http://www.u148.net' + $(this).find('h1 a').attr('href');
	eachTitle = $(this).find('h1 a').text();
	eachWriter = $(this).find('.index-time a').text();
	eachSummary = $(this).find(".summary").text();
	eachData = $(this).find('.data-text').text().replace('推荐于:', '');
	eachLook = $(this).find(".data-right").text();

	singleContext.push(JSON.stringify({
		"eachUrl": eachUrl,
		"eachTitle": eachTitle,
		"eachWriter": eachWriter,
		"eachSummary": eachSummary,
		"eachData": eachData,
		"eachLook": eachLook
	}));

})

fs.appendFile('u1483.txt', singleContext, 'utf8');

}

fetch();

可以参考下callback实现的

var fs = require('fs');
var path = require('path');
var slog = require('single-line-log').stdout;
var EventEmitter = require("events").EventEmitter;
var util = require("util");
var cheerio = require("cheerio");
var superagent = require("superagent");
const charset = require("superagent-charset");
charset(superagent);

function mkdir(sres, callback) {
    var $ = cheerio.load(sres.text);
    var eachUrl;
    var eachTitle;
    var eachWriter;
    var eachSummary;
    var eachData;
    var eachLook;
    var singleContext = [];

    $('.list-content').each(function() {
        eachUrl = 'http://www.u148.net' + $(this).find('h1 a').attr('href');
        eachTitle = $(this).find('h1 a').text();
        eachWriter = $(this).find('.index-time a').text();
        eachSummary = $(this).find(".summary").text();
        eachData = $(this).find('.data-text').text().replace('推荐于:', '');
        eachLook = $(this).find(".data-right").text();

        singleContext.push(JSON.stringify({
            "eachUrl": eachUrl,
            "eachTitle": eachTitle,
            "eachWriter": eachWriter,
            "eachSummary": eachSummary,
            "eachData": eachData,
            "eachLook": eachLook
        }));

    })

    fs.appendFile('u1483.txt', singleContext, 'utf8', function(err) {
        callback();
    });

}


function ProgressBar(description, bar_length) {
    this.description = description || 'Progress';
    this.length = bar_length || 25;
    this.render = function(opts) {
        var percent = (opts.completed / opts.total).toFixed(4);
        var cell_num = Math.floor(percent * this.length);
        var cell = '';
        for (var i = 0; i < cell_num; i++) cell += '█';
        var empty = '';
        for (var i = 0; i < this.length - cell_num; i++) empty += '░';
        var cmdText = this.description + ': ' + (100 * percent).toFixed(2) + '% ' + cell + empty + ' ' + opts.completed + '/' + opts.total;
        slog(cmdText);
    };
}


function TaskManger(tasks, getTask, limit) {
    if (!(this instanceof TaskManger))
        return new TaskManger(tasks, getTask, limit);
    EventEmitter.call(this);
    this.tasks = tasks || [];
    this.limit = limit || 2;
    this.total = this.sum = tasks.length;
    this.getTask = getTask || function(value, callback) {
        callback();
    }
}
TaskManger.prototype.complete = function() {
    this.emit('complete');
}
TaskManger.prototype.progress = function() {
    this.emit('progress', {
        completed: this.total,
        total: this.sum
    });
}
TaskManger.prototype.start = function() {
    var limit = Math.min(this.limit, this.tasks.length);
    for (var i = 0; i < limit; i++) this.runTask();
    return this;
}
TaskManger.prototype.finish = function(err) {
    this.total--;
    this.progress();
    if (this.total == 0)
        return this.complete();
    this.runTask();
    return this;
}
TaskManger.prototype.runTask = function() {
    var task = this.tasks.shift();
    if (task) this.getTask(task, this.finish.bind(this));
    return this;
}
util.inherits(TaskManger, EventEmitter);

Array.prototype.taskstart = function(getTask, limit) {
    var self = this;
    var bar = new ProgressBar('爬取进度', 50);
    return TaskManger(self, getTask, limit).on("progress", function(progress) {
        bar.render(progress);
    }).on("complete", function() {
        console.log("finish");
    }).start();

};
Array.range = function(start, end, step) {
    var result = [],
        step = step || 1;
    for (let i = start; i < end; i += step) result.push(i);
    return result;
}

Array.range(1, 1318).taskstart(function(value, callback) {

    superagent.get('http://www.u148.net/list/' + value)
        .charset('utf8')
        .end(function(err, sres) {
            if (err) {
                callback();
                return;
            }
            mkdir(sres, callback);
        });

}, 20)



用这个 promise.map 包

const promise = pmap(arr, async item => {
  // 
}, 10) // 最后是 concurrency

其实和 async.parallelLimit 一样 可以使用 bluebird Promise.map, 不喜欢和 bluebird 绑死的用我写的这个 promise.map包即可

@MiYogurt @Sunshine168 function getPage(singeUrl) { return new Promise((resolve,reject)=>{ superagent.get(singeUrl) .set({‘Content-Type’: ‘application/json’, ‘User-Agent’: ‘Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.96 Safari/537.36’}) .charset(‘utf8’) .end(function (err, sres) { if (err) throw err; utils.singleRequest(sres,db) }); resolve(‘resolve==’+singeUrl) }) } let flag = true; pages.forEach((item) => { if(flag){ flag = false; let promises = item.map(function (url) { return getPage(url); }); Promise.all(promises).then(res => { flag = true; }) } }) 就按照您说的这种办法,每次取五个url,如果都成功,flag=false,但是事实确实flag永远等于false;;;是我哪里写错了么

const stream = [
	new Promise((yes)=> setTimeout(() => yes(20), 2000)),
	new Promise((yes)=> setTimeout(() => yes(30), 1000)),
	new Promise((yes)=> setTimeout(() => yes(40), 2000)),
	new Promise((yes)=> setTimeout(() => yes(50), 2000)),
	new Promise((yes)=> setTimeout(() => yes(60), 2000)),
	new Promise((yes)=> setTimeout(() => yes(70), 5000))
]


function run() {
  
    let i = -1;
    
    function dispatch(i){
      index = i;
      if(index >= stream.length){
        return
      }
      return Promise.all(
        [stream[i], stream[i+1]]
      ).then((arr) => {
        console.log(arr)
        console.log(i)
        return dispatch(i+2)
      })
    }
  
    return dispatch(0)
}

run()


const stream = [
    new Promise((yes)=> setTimeout(() => yes(20), 5000)),
    new Promise((yes)=> setTimeout(() => yes(30), 6000)),
    new Promise((yes)=> setTimeout(() => yes(40), 2000)),
    new Promise((yes)=> setTimeout(() => yes(50), 2000)),
    new Promise((yes)=> setTimeout(() => yes(60), 4000)),
    new Promise((yes)=> setTimeout(() => yes(70), 4000))
]


async function run() {
    for (let i = 0 ;i < stream.length; i+=2){
      console.log(i)
      let arr = await Promise.all([stream[i], stream[i+1]]);
      console.log(arr)
    }
}

run()

image.png

通过事件分发也不错。

连个 markdown 都格式化不好,哎,算了。

@MiYogurt 谢谢小哥,,解决了

既然不想用类库, 那就自己写个队列控制并发

不想用库,那就把 https://github.com/sindresorhus/promise-fun 对应的方法,CTRL+C 过来呗 -.-!!

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