如何使用 async/await 实现命令模式 [英] How to implement Command Pattern with async/await

问题描述

我目前正在升级一些现有代码以供 windows Universal 使用，并且正在努力转换命令模式以使用新的 async/await 功能.

i'm currently upgrading some existing code for use by windows universal and am struggling to convert a command pattern to work with the new async/await functionality.

我有一个命令调度程序类，它在自己的线程中运行并处理已添加到其队列中的命令.有问题的方法如下所示:

I have a command scheduler class that runs within its own thread and processes commands that have been added to its queue. The method in question looks like this:

private List<ICommandItem> _items;

private void ProcessCommands()
{
    while(_items.count > 0)
    {
        _items[0].Execute();
        _items.RemoveAt(0);
    }
}

我的问题是我的一些 ICommandItem.Execute() 方法现在需要异步，因为它们涉及文件 io 而其他方法没有异步方法.我如何修改上述模式，以便:

My problem is that some of my ICommandItem.Execute() methods now need to be async because they involve file io whilst others have no async methods. How could I modify the above pattern so that:

1. 我的执行程序可以处理异步和非异步 ICommandItems
2. 执行器仅在上一个命令完成后才开始执行命令.

我很乐意同步执行这些方法，但现在到处都会导致死锁.

I would be happy to just execute the methods synchronously but that now causes deadlocks everywhere.

推荐答案

我的问题是我的一些 ICommandItem.Execute() 方法现在需要异步，因为它们涉及文件 io 而其他方法没有异步方法.

My problem is that some of my ICommandItem.Execute() methods now need to be async because they involve file io whilst others have no async methods.

从技术上讲，异步(Task-returning)签名仅意味着实现可能是异步的.因此，虽然您可以引入单独的异步接口，但另一种方法是将现有接口更改为 Task-returning:

Technically, an asynchronous (Task-returning) signature only means that the implementation may be asynchronous. So, while you can introduce a separate asynchronous interface, another approach is to change the existing interface to be Task-returning:

interface ICommandItem
{
  Task ExecuteAsync(); // Used to be "void Execute();"
}

你的同步实现将不得不改变以返回一个Task:

Your synchronous implementations will have to change to return a Task:

Task ICommandItem.ExecuteAsync()
{
  // Do synchronous work.
  return Task.CompletedTask; // If you're not on 4.6 yet, you can use "Task.FromResult(0)"
}

虽然异步实现很简单:

async Task ICommandItem.ExecuteAsync()
{
  await ...; // Do asynchronous work.
}

而你的跑步者"可以使用 await :

And your "runner" can just use await:

private async Task ProcessCommandsAsync()
{
  while(_items.count > 0)
  {
    await _items[0].ExecuteAsync();
    _items.RemoveAt(0);
  }
}

这篇关于如何使用 async/await 实现命令模式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！