javascript - 在 Meteor 1.3+ 中使用异步

Question

大家好，我想使用 Async NPM package和 eachLimit function在 Meteor 1.3+ 中，我后来在没有 Meteor 的情况下使用了它，如下所示，效果很好:

var items = ["test", "test2","test3","test4","test5","test6","test7","test8","test9","test10","test11","test12","test13","test14","test15","test16","test17","test18","test19","test20"];
async.eachLimit(items, 5, (item, callback) => {
                        try {
                            //console.log(item);
                            heavyProcess(item);
                        }
                        catch (e) {
                            return callback(e);
                        }
                        callback();
                    }, (err) => {
                        if (err) console.error(err.message);
                    });
function heavyProcess(item) {
setTimeout(function () {
            console.log(item);
        }, Math.floor(Math.random() * 10000));
}

您可以在这里看到:https://jsfiddle.net/g0L90f3h/

这是上面的代码输出:

test3
test8
test18
test5
test20
test15
test19
test
test9
test11
test14
test17
test2
test12
test4
test10
test13
test7
test16
test6

以上输出完全正确。现在我将上面的代码迁移到 Meteor，如下所示:

// startup.js
import async from 'async';
let items = ["test", "test2","test3","test4","test5","test6","test7","test8","test9","test10","test11","test12","test13","test14","test15","test16","test17","test18","test19","test20"];
            async.eachLimit(items, 5, (item, callback) => {
                try {
                    my_utils.heavyProcessSimulator(item);
                }
                catch (e) {
                    return callback(e);
                }
                callback();
            }, (err) => {
                if (err) console.error(err.message);
            });

// my_utils.js
    heavyProcessSimulator(item) {
        Meteor._sleepForMs(Math.floor(Math.random() * 10000));
        console.log(item);
    }

但是下面的输出是错误的:

I20160802-18:25:07.959(4.5)? test
I20160802-18:25:15.477(4.5)? test2
I20160802-18:25:20.915(4.5)? test3
I20160802-18:25:28.284(4.5)? test4
I20160802-18:25:31.842(4.5)? test5
I20160802-18:25:35.694(4.5)? test6
I20160802-18:25:38.871(4.5)? test7
I20160802-18:25:48.812(4.5)? test8
I20160802-18:25:52.452(4.5)? test9
I20160802-18:25:58.944(4.5)? test10
I20160802-18:26:06.411(4.5)? test11
I20160802-18:26:08.461(4.5)? test12
I20160802-18:26:09.135(4.5)? test13
I20160802-18:26:17.474(4.5)? test14
I20160802-18:26:24.613(4.5)? test15
I20160802-18:26:31.605(4.5)? test16
I20160802-18:26:34.022(4.5)? test17
I20160802-18:26:36.792(4.5)? test18
I20160802-18:26:39.646(4.5)? test19
I20160802-18:26:41.706(4.5)? test20

为什么会发生这种情况以及如何解决这个问题？我测试了很多东西但没有发现问题。为什么要同步运行？

编辑:

<小时/>

非常感谢@hwillson 提供的精彩答案，我更改了代码，如下所示，但输出仍然错误。这是我的新代码:

import async from 'async';
const items = ["test", "test2", "test3", "test4", "test5", "test6", "test7", "test8", "test9", "test10", "test11", "test12", "test13", "test14", "test15", "test16", "test17", "test18", "test19", "test20"];

        async function heavyProcessSimulator(item) {
            console.log("Process Start for: " + item);
            Meteor._sleepForMs(Math.floor(Math.random() * 10000));
            console.log("Process Finished for: " + item);
        }

        async.eachLimit(items, 5, (item, callback) => {
            try {
                heavyProcessSimulator(item);
            } catch (e) {
                return callback(e);
            }
            callback();
        }, (err) => {
            if (err) console.error(err.message);
        });

这是输出:

I20160805-13:45:00.014(4.5)? Process Start for: test
I20160805-13:45:00.014(4.5)? Process Start for: test2
I20160805-13:45:00.015(4.5)? Process Start for: test3
I20160805-13:45:00.015(4.5)? Process Start for: test4
I20160805-13:45:00.016(4.5)? Process Start for: test5
I20160805-13:45:00.016(4.5)? Process Start for: test6
I20160805-13:45:00.017(4.5)? Process Start for: test7
I20160805-13:45:00.017(4.5)? Process Start for: test8
I20160805-13:45:00.018(4.5)? Process Start for: test9
I20160805-13:45:00.023(4.5)? Process Start for: test10
I20160805-13:45:00.024(4.5)? Process Start for: test11
I20160805-13:45:00.024(4.5)? Process Start for: test12
I20160805-13:45:00.025(4.5)? Process Start for: test13
I20160805-13:45:00.025(4.5)? Process Start for: test14
I20160805-13:45:00.026(4.5)? Process Start for: test15
I20160805-13:45:00.026(4.5)? Process Start for: test16
I20160805-13:45:00.027(4.5)? Process Start for: test17
I20160805-13:45:00.027(4.5)? Process Start for: test18
I20160805-13:45:00.028(4.5)? Process Start for: test19
I20160805-13:45:00.029(4.5)? Process Start for: test20
I20160805-13:45:00.665(4.5)? Process Finished for: test19
I20160805-13:45:00.744(4.5)? Process Finished for: test2
I20160805-13:45:00.841(4.5)? Process Finished for: test
I20160805-13:45:00.917(4.5)? Process Finished for: test11
I20160805-13:45:02.438(4.5)? Process Finished for: test4
I20160805-13:45:02.953(4.5)? Process Finished for: test5
I20160805-13:45:04.727(4.5)? Process Finished for: test3
I20160805-13:45:05.510(4.5)? Process Finished for: test8
I20160805-13:45:05.562(4.5)? Process Finished for: test7
I20160805-13:45:05.849(4.5)? Process Finished for: test16
I20160805-13:45:06.231(4.5)? Process Finished for: test17
I20160805-13:45:06.527(4.5)? Process Finished for: test12
I20160805-13:45:06.959(4.5)? Process Finished for: test18
I20160805-13:45:07.147(4.5)? Process Finished for: test10
I20160805-13:45:07.313(4.5)? Process Finished for: test13
I20160805-13:45:08.027(4.5)? Process Finished for: test6
I20160805-13:45:08.736(4.5)? Process Finished for: test15
I20160805-13:45:08.912(4.5)? Process Finished for: test9
I20160805-13:45:08.962(4.5)? Process Finished for: test20
I20160805-13:45:08.975(4.5)? Process Finished for: test14

如您所见，上面的代码现在可以异步工作，但仍然limit不正确。它首先调用所有 20 个项目，然后进行处理。

Answer 1

Meteor 1.3+ 内置了 async/await 支持(在客户端和服务器上)，这要归功于 Meteor ecmascript包裹。您不需要使用第 3 方包来异步运行代码。例如:

服务器示例:/server/main.js

import { Meteor } from 'meteor/meteor';

const items = [
  "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8", 
  "test9", "test10", "test11", "test12", "test13", "test14", "test15", 
  "test16", "test17", "test18", "test19", "test20"
];

async function heavyProcessSimulator(item) {
  Meteor._sleepForMs(Math.floor(Math.random() * 10000));
  console.log(item);
}

items.forEach((item) => {
  heavyProcessSimulator(item);
});

示例输出:

I20160802-15:15:47.220(-4)? test16
I20160802-15:15:47.959(-4)? test9
I20160802-15:15:48.331(-4)? test18
I20160802-15:15:49.183(-4)? test7
I20160802-15:15:49.211(-4)? test13
I20160802-15:15:49.289(-4)? test14
I20160802-15:15:49.587(-4)? test
I20160802-15:15:49.776(-4)? test17
I20160802-15:15:51.195(-4)? test15
...

客户端示例:/client/main.js

const items = [
  "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8",
  "test9", "test10", "test11", "test12", "test13", "test14", "test15",
  "test16", "test17", "test18", "test19", "test20"
];

async function heavyProcessSimulator(item) {
  setTimeout(() => {
    console.log(item);
  }, (Math.floor(Math.random() * 10000)));  
}

items.forEach((item) => {
  heavyProcessSimulator(item);
});

示例输出:

test16
test19
test14
test2
test3
test11
test9
test10
...

只需确保您已安装 ecmascript 软件包(默认情况下，Meteor 1.3+ 项目应安装该软件包，但以防万一:meteor add ecmascript)。

您可以将 Meteor 的 async 支持与 async 的功能结合起来。 npm 包。下面是一个修改后的示例，展示了如何使用 async.eachLimit:

服务器示例:/server/main.js

import { Meteor } from 'meteor/meteor';
import async from 'async';

const items = [
  "test", "test2", "test3", "test4", "test5", "test6", "test7", "test8",
  "test9", "test10", "test11", "test12", "test13", "test14", "test15",
  "test16", "test17", "test18", "test19", "test20"
];

async function heavyProcessSimulator(item, callback) {
  Meteor._sleepForMs(Math.floor(Math.random() * 10000));
  console.log(item);
  callback();
}

async.eachLimit(items, 5, (item, callback) => {
  try {
    heavyProcessSimulator(item, callback);
  } catch (e) {
    return callback(e);
  }
}, (err) => {
  if (err) console.error(err.message);
});