对多个任务使用 async/await [英] Using async/await for multiple tasks

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本文介绍了对多个任务使用 async/await的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我使用的是完全异步的 API 客户端,也就是说,每个操作要么返回 Task 要么返回 Task,例如:

static async Task DoSomething(int siteId, int postId, IBlogClient client){等待 client.DeletePost(siteId, postId);//调用API客户端Console.WriteLine("已删除帖子 {0}.", siteId);}

使用 C# 5 async/await 运算符,启动多个任务并等待它们全部完成的正确/最有效方法是什么:

int[] ids = new[] { 1, 2, 3, 4, 5 };Parallel.ForEach(ids, i => DoSomething(1, i, blogClient).Wait());

或:

int[] ids = new[] { 1, 2, 3, 4, 5 };Task.WaitAll(ids.Select(i => DoSomething(1, i, blogClient)).ToArray());

由于 API 客户端在内部使用 HttpClient,我希望这会立即发出 5 个 HTTP 请求,并在每个请求完成时写入控制台.

解决方案

int[] ids = new[] { 1, 2, 3, 4, 5 };Parallel.ForEach(ids, i => DoSomething(1, i, blogClient).Wait());

尽管您与上述代码并行运行操作,但此代码会阻塞每个操作运行的每个线程.例如,如果网络调用需要 2 秒,则每个线程挂起 2 秒,不做任何事情,除了等待.

int[] ids = new[] { 1, 2, 3, 4, 5 };Task.WaitAll(ids.Select(i => DoSomething(1, i, blogClient)).ToArray());

另一方面,上面带有 WaitAll 的代码也会阻塞线程,并且您的线程在操作结束之前将无法自由处理任何其他工作.

推荐方法

我更喜欢 WhenAll 它将并行异步执行您的操作.

public async Task DoWork() {int[] ids = new[] { 1, 2, 3, 4, 5 };await Task.WhenAll(ids.Select(i => DoSomething(1, i, blogClient)));}

<块引用>

事实上,在上面的例子中,你甚至不需要await,你可以直接从方法中返回,因为你没有任何continuations:

公共任务DoWork(){int[] ids = new[] { 1, 2, 3, 4, 5 };return Task.WhenAll(ids.Select(i => DoSomething(1, i, blogClient)));}

为了支持这一点,这里有一篇详细的博客文章替代方案及其优点/缺点:如何以及在何处使用 ASP.NET Web API 并发异步 I/O

I'm using an API client that is completely asynchrounous, that is, each operation either returns Task or Task<T>, e.g:

static async Task DoSomething(int siteId, int postId, IBlogClient client)
{
    await client.DeletePost(siteId, postId); // call API client
    Console.WriteLine("Deleted post {0}.", siteId);
}

Using the C# 5 async/await operators, what is the correct/most efficient way to start multiple tasks and wait for them all to complete:

int[] ids = new[] { 1, 2, 3, 4, 5 };
Parallel.ForEach(ids, i => DoSomething(1, i, blogClient).Wait());

or:

int[] ids = new[] { 1, 2, 3, 4, 5 };
Task.WaitAll(ids.Select(i => DoSomething(1, i, blogClient)).ToArray());

Since the API client is using HttpClient internally, I would expect this to issue 5 HTTP requests immediately, writing to the console as each one completes.

解决方案

int[] ids = new[] { 1, 2, 3, 4, 5 };
Parallel.ForEach(ids, i => DoSomething(1, i, blogClient).Wait());

Although you run the operations in parallel with the above code, this code blocks each thread that each operation runs on. For example, if the network call takes 2 seconds, each thread hangs for 2 seconds w/o doing anything but waiting.

int[] ids = new[] { 1, 2, 3, 4, 5 };
Task.WaitAll(ids.Select(i => DoSomething(1, i, blogClient)).ToArray());

On the other hand, the above code with WaitAll also blocks the threads and your threads won't be free to process any other work till the operation ends.

Recommended Approach

I would prefer WhenAll which will perform your operations asynchronously in Parallel.

public async Task DoWork() {

    int[] ids = new[] { 1, 2, 3, 4, 5 };
    await Task.WhenAll(ids.Select(i => DoSomething(1, i, blogClient)));
}

In fact, in the above case, you don't even need to await, you can just directly return from the method as you don't have any continuations:

public Task DoWork() 
{
    int[] ids = new[] { 1, 2, 3, 4, 5 };
    return Task.WhenAll(ids.Select(i => DoSomething(1, i, blogClient)));
}

To back this up, here is a detailed blog post going through all the alternatives and their advantages/disadvantages: How and Where Concurrent Asynchronous I/O with ASP.NET Web API

这篇关于对多个任务使用 async/await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!

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