.net Core Parallel.ForEach 问题 [英] .net Core Parallel.ForEach issues

问题描述

我已为某些项目切换到 .net Core，但现在在使用 Parallel.ForEach 时遇到了问题.在过去，我经常有一个 id 值列表，然后我会用它来发出 Web 请求以获取完整数据.它看起来像这样:

I've switched over to .net Core for some projects and am now having a problem with Parallel.ForEach. In the past I often had a List of id values which I then would use to make web requests in order to get the full data. It would look something like this:

Parallel.ForEach(myList, l =>
{
    // make web request using l.id 
    // process the data somehow
});

好吧，在 .net Core 中，Web 请求必须全部标记为 await，这意味着 Parallel.ForEach 操作必须标记为 async.但是，将 Parallel.ForEach 操作标记为 async 意味着我们有一个导致问题的 void async 方法.在我的特殊情况下，这意味着响应在并行循环中的所有 Web 请求完成之前返回到应用程序，这既尴尬又导致错误.

Well, in .net Core the web requests must all be tagged await which means the Parallel.ForEach action must be tagged with async. But, tagging a Parallel.ForEach action as async means we have a void async method which causes issues. In my particular case that means the response returns to the application before all of the web requests in the Parallel loop are completed which is both awkward and causes errors.

问题:在此处使用 Parallel.ForEach 的替代方法有哪些?

Question: What are the alternatives to using Parallel.ForEach here?

我发现的一个可能的解决方案是将 Parallel 循环包装在 Task 中并等待任务:

One possible solution I found was to wrap the Parallel loop inside of a Task and await the task:

await Task.Run(() => Parallel.ForEach(myList, l =>
{
    // stuff here
}));

(在此处找到:Parallel.ForEach 与 Task.Run 和 Task.WhenAll)

但是，这对我不起作用.当我使用它时，我仍然会在循环完成之前返回到应用程序.

But, that isn't working for me. When I use that I still end up returning to the application before the loop is completed.

另一种选择:

var tasks = new List<Task>();
foreach (var l in myList)
{
    tasks.Add(Task.Run(async () =>
    {
         // stuff here
    }));
}
await Task.WhenAll(tasks);

这似乎有效，但这是唯一的选择吗?新的 .net Core 似乎使 Parallel.ForEach 几乎毫无用处(至少在嵌套 Web 调用方面).

This appears to work, but is that the only option? It seems that the new .net Core has rendered Parallel.ForEach virtually useless (at least when it comes to nested web calls).

感谢任何帮助/建议.

推荐答案

这 3 个方法都不好.

Neither of those 3 apporaches are good.

在这种情况下，您不应使用 Parallel 类或 Task.Run.

You should not use the Parallel class, or Task.Run on this scenario.

相反，有一个 async 处理程序方法:

Instead, have an async handler method:

private async Task HandleResponse(Task<HttpResponseMessage> gettingResponse)
{
     HttpResponseMessage response = await gettingResponse;
     // Process the data
}

然后使用Task.WhenAll:

Task[] requests = myList.Select(l => SendWebRequest(l.Id))
                        .Select(r => HandleResponse(r))
                        .ToArray();

await Task.WhenAll(requests);

这篇关于.net Core Parallel.ForEach 问题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！