为什么控件不会在第一次等待

时间：2018-03-13 03:29:58

标签： c# async-await

我不确定我对Await的理解是对的。输出顺序与我的预期不同。

这是主叫代码。

internal class Program
{
    private static void Main(string[] args)
    {
        var levelOne = new LevelOne();
        levelOne.Work();
        Console.WriteLine("Waiting for answer...");
        Console.ReadLine();
    }
}

这是LevelOne类

public class LevelOne
{
    public async void Work()
    {
        Console.WriteLine("Starting work.");
        await LevelTwo.SomeRandomWork();
        Console.WriteLine("Work done.");
    }
}

最后这是LevelTwo类

public class LevelTwo
{
    public static async Task SomeRandomWork()
    {
        Thread.Sleep(5000);
        Console.WriteLine("Here I am");
        var someRandomNumber = await KillTime();
        Console.WriteLine("Answer " + someRandomNumber);
        someRandomNumber = await KillTime();
        Console.WriteLine("Answer again: " + someRandomNumber);
    }

    private static async Task<long> KillTime()
    {
        await Task.Delay(TimeSpan.FromMilliseconds(5000));
        Random random = new Random();
        return random.Next(100000, 900000);
    }
}

我看到的是

Starting work.
Here I am
Waiting for answer...
Answer 352100
Answer again: 453356
Work done.

这是我期望的输出。

Starting work.
Waiting for answer...
Here I am
Answer 141710
Answer again: 530010
Work done.

在LevelOne的工作方法中等待后，控件是否应该返回到调用者代码？在LevelTwo被击中之前，控件不会再回来。

2 个答案:

答案 0 :(得分：1)

这是因为您在Thread.Sleep内使用的是await Task.Delay(...)而不是SomeRandomWork()。这就是为什么在await SomeRandomWork()内await产生控件之前，Work()内public static async Task SomeRandomWork() { await Task.Delay(1000); Console.WriteLine("Here I am"); var someRandomNumber = await KillTime(); Console.WriteLine("Answer " + someRandomNumber); someRandomNumber = await KillTime(); Console.WriteLine("Answer again: " + someRandomNumber); } 内的第一个Starting work. Waiting for answer... Here I am Answer 598694 Answer again: 353771 Work done. 代码同步执行的原因：

{
  "name": "angular-quickstart",
  "version": "1.0.0",
  "description": "QuickStart package.json from the documentation, supplemented with testing support",
  "scripts": {
    "build": "tsc -p src/",
    "build:watch": "tsc -p src/ -w",
    "build:e2e": "tsc -p e2e/",
    "serve": "lite-server -c=bs-config.json",
    "serve:e2e": "lite-server -c=bs-config.e2e.json",
    "prestart": "npm run build",
    "start": "concurrently \"npm run build:watch\" \"npm run serve\"",
    "pree2e": "npm run build:e2e",
    "e2e": "concurrently \"npm run serve:e2e\" \"npm run protractor\" --kill-others --success first",
    "preprotractor": "webdriver-manager update",
    "protractor": "protractor protractor.config.js",
    "pretest": "npm run build",
    "test": "concurrently \"npm run build:watch\" \"karma start karma.conf.js\"",
    "pretest:once": "npm run build",
    "test:once": "karma start karma.conf.js --single-run",
    "lint": "tslint ./src/**/*.ts -t verbose"
  },
  "keywords": [],
  "author": "",
  "license": "MIT",
  "dependencies": {
    "@angular/common": "~4.1.3",
    "@angular/compiler": "~4.1.3",
    "@angular/core": "~4.1.3",
    "@angular/forms": "~4.1.3",
    "@angular/http": "~4.1.3",
    "@angular/platform-browser": "~4.1.3",
    "@angular/platform-browser-dynamic": "~4.1.3",
    "@angular/router": "~4.1.3",
    "@types/chart.js": "^2.7.2",
    "angular-2-data-table": "^0.1.2",
    "angular-in-memory-web-api": "~0.3.0",
    "angular2-adal": "^0.1.4",
    "angular2-csv": "^0.2.5",
    "chart.js": "^2.7.1",
    "core-js": "^2.4.1",
    "jquery": "^3.2.1",
    "ng-editable-table": "^0.3.15",
    "ng2-accordion": "0.0.15",
    "ng2-adal": "^0.2.6",
    "ng2-bs3-modal": "^0.10.4",
    "ng2-charts": "^1.6.0",
    "ng2-smart-table": "^1.2.2",
    "rxjs": "5.0.1",
    "systemjs": "0.20.13",
    "zone.js": "^0.8.4"
  },
  "devDependencies": {
    "@types/jasmine": "2.5.51",
    "@types/node": "^7.0.28",
    "angular2-datatable": "^0.6.0",
    "angular2-modal": "^2.0.3",
    "ng2-bs3-modal": "0.10.4",
    "ng2-accordion": "0.0.15",
    "bootstrap-daterangepicker": "^2.1.25",
    "canonical-path": "0.0.2",
    "concurrently": "^3.2.0",
    "daterange": "^0.3.0",
    "daterangepicker": "^2.1.25",
    "jasmine-core": "~2.6.2",
    "jquery": "^3.2.1",
    "karma": "^1.3.0",
    "karma-chrome-launcher": "^2.0.0",
    "karma-cli": "^1.0.1",
    "karma-jasmine": "^1.0.2",
    "karma-jasmine-html-reporter": "^0.2.2",
    "lite-server": "^2.2.2",
    "lodash": "^4.17.4",
    "protractor": "~5.1.2",
    "rimraf": "^2.5.4",
    "tslint": "^5.4.3",
    "typescript": "~2.3.4",
    "typings": "^2.1.1"
  },
  "repository": {}
}

进行切换后，输出会更改为您的预期：

/**
 * System configuration for Angular samples
 * Adjust as necessary for your application needs.
 */
(function (global) {
  System.config({
    paths: {
      // paths serve as alias
      'npm:': '/node_modules/'
    },
    // map tells the System loader where to look for things
    map: {
      // our app is within the app folder
      'app': 'app',
      'directive': 'directives',
      // angular bundles
      '@angular/core': 'npm:@angular/core/bundles/core.umd.js',
      '@angular/common': 'npm:@angular/common/bundles/common.umd.js',
      '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js',
      '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js',
      '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
      '@angular/http': 'npm:@angular/http/bundles/http.umd.js',
      '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
      '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',
      'ng2-bs3-modal': 'npm:ng2-bs3-modal',
      "ng2-accordion": "../../node_modules/ng2-accordion",
      'angular-2-data-table': 'npm:angular-2-data-table/dist',
      'ng2-charts': 'npm:ng2-charts/bundles/ng2-charts.umd.js',
      'chart.js': 'npm:chart.js/dist/Chart.bundle.js',
      

      'ng2-bs3-modal': 'npm:ng2-bs3-modal',
      "ng2-accordion": "../../node_modules/ng2-accordion",
      // other libraries
      'rxjs': 'npm:rxjs',
      'angular-in-memory-web-api': 'npm:angular-in-memory-web-api/bundles/in-memory-web-api.umd.js',
      'angular2-datatable': 'npm:angular2-datatable',
      'lodash': 'npm:lodash/lodash.js',
      'ng2-adal': 'npm:ng2-adal',
      'adal': 'npm:adal-angular/lib',
      'adal-angular': 'npm:adal-angular/lib',
      'angular2-csv': 'npm:angular2-csv',
      'ng2-smart-table': 'npm:ng2-smart-table',
      'ng2-completer': 'npm:ng2-completer',

    },
    // packages tells the System loader how to load when no filename and/or no extension
    packages: {
        'chart.js': {defaultExtension: 'js' },
        'ng2-charts': { defaultExtension: 'js' },
        'jquery': { main: 'jquery.js', defaultExtension: 'js' },
        'ng2-smart-table': { main: 'bundles/table.umd.js', defaultExtension: 'js' },
        'ng2-completer': { main: 'ng2-completer.umd.js', defaultExtension: 'js' },
        'angular-2-data-table': {
            format: 'cjs',
            defaultExtension: 'js',
            main: 'index.js'
        },
        'angular2-datatable': {
            main: 'index.js',
            defaultExtension: 'js'
        },
        'lodash': { defaultExtension: 'js' },
        'ng2-accordion': { main: 'index.js', defaultExtension: "js" },
        'ng2-bs3-modal': { main: 'ng2-bs3-modal.js', defaultExtension: "js" },
        'directive': { defaultExtension: 'js' },
        'ng2-accordion': { main: 'index.js', defaultExtension: "js" },
        'ng2-bs3-modal': { main: 'ng2-bs3-modal.js', defaultExtension: "js" },
        'ng2-adal': { main: 'core.js', defaultExtension: 'js' },
        'adal-angular': { main: 'adal-angular', defaultExtension: 'js' },
        'adal': { main: 'adal.js', defaultExtension: 'js' },
        'angular2-csv': { main: 'Angular2-csv', defaultExtension: 'js' },
        //'ng2-daterangepicker': {
        //    main: 'index',
        //    defaultExtension: 'js'
        //},
        //moment: {
        //    main: 'moment',
        //    defaultExtension: 'js'
        //},
      app: {
        defaultExtension: 'js',
        meta: {
          './*.js': {
            loader: 'systemjs-angular-loader.js'
          }
        }
      },
      'rxjs': {
        main: 'Rx.js',
        defaultExtension: 'js'
      }
    }
  });
})(this);

答案 1 :(得分：0)

虽然没有解决您的实际问题，但这可能对某人有用

  

await关键字使运行时对新操作运行操作   task并使执行线程返回并继续执行   执行。 （在大多数情况下，它执行的主线程   应用）。 等待操作完成后，返回到   它停止的声明（换句话说，它返回给调用者，   换句话说，它根据保存的状态返回并开始   执行报表。

所以await等待新任务完成，并确保等待任务执行完成后继续。

await关键字与async一起用于执行异步编程。它被称为异步编程，因为运行时在遇到await关键字时（类似于迭代器中的yield）捕获程序的状态，并且恢复在等待的任务完成后返回状态，以便继续在正确的上下文中运行。

它在某些方面类似于Task ContinueWith

然而，ContinueWith和await之间的一些显着差异是

  • 保存状态并返回执行上下文

    • ContinueWith不保存任何类型的状态，如果未提供调度程序，则使用默认线程调度程序上的ContinueWith运行附加延续操作。

      < / LI>

    • await遇到此关键字时，状态会被保存，一旦完成task的{​​{1}}完成，其执行流程将获取已保存的状态数据并启动await之后的执行语句。 （注意：州正在详细说明await / executioncontext。）。

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