在 Meteor 1.3+ 中使用异步答案

【问题标题】：using Async in Meteor 1.3+在 Meteor 1.3+ 中使用异步
【发布时间】：2016-12-07 22:29:09
【问题描述】：

大家好，我想在 Meteor 1.3+ 中使用 Async NPM package 和 eachLimit function 我后来在没有 Meteor 的情况下使用它，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));
}

你可以在这里看到这个：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

上面的输出是完全正确的。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);
    }

但它在输出下方的返回是错误的：

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？我测试了很多东西，但没有发现问题。为什么要运行同步？

编辑：

非常感谢@hwillson 提供了很棒的答案，我像下面这样更改了我的代码，但输出仍然是错误的。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 async 现在可以工作，但 limit 仍然不正确。它首先调用所有 20 个项目，然后处理。

【问题讨论】：

这是因为Meteor._sleepForMs 是阻塞的，而setTimeout 是非阻塞的。看看这个：github.com/nodejs/node/blob/master/doc/topics/…
感谢您的关注。但我使用eachLimit 来异步执行此循环。
我认为当我们使用async.eachLimit 时，timeout 或Meteor._sleepForMs 之间并不重要，因为它是异步的，它完全可以作为异步工作。对吗？

标签： javascript node.js asynchronous meteor async.js

【解决方案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。您不需要使用 3rd 方包来异步运行您的代码。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);
});

样本输出：

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);
});

样本输出：

test16
test19
test14
test2
test3
test11
test9
test10
...

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

您可以将 Meteor 的 async 支持与 async npm 包中的功能结合起来。这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);
});

【讨论】：

感谢您的回答。它运行良好，现在我的代码是异步的，但我还需要eachLimit 限制行为，我需要运行我的进程五乘五。我该如何处理？ await 可以吗？
我已经修改了我的答案，以展示如何将 Meteor 的 async 功能与 async.eachLimit 一起使用。
嗨@hwillson，非常感谢您的重播。正如您在上面所说的，我更改了我的代码。异步问题已修复，但 limit 仍然无法正常工作。我用新的Edit 部分编辑我的问题并添加新的输出。我将console's 更改为heavyProcessSimulator 以清除问题。
@b24 - 我更新了我的示例来展示如何解决这个问题。将callback() 移出eachLimit iteratee 函数，并将其作为参数传递给heavyProcessSimulator。然后在heavyProcessSimulator函数完成时调用它，这样eachLimit就知道它已经完成了，可以开始下一次调用了。