如何在C＃中运行多个任务？

Question

How to modify the following code and make it runs multiple tasks concurrently?

foreach (SyndicationItem item in CurrentFeed.Items)
{
    if (m_bDownloadInterrupted)
    break;

    await Task.Run( async () =>
    {
        // do some downloading and processing work here
        await DoSomethingAsync();
    }
}

I also need to make interruption and stop the process possible. Because my DoSomethingAsync method reads the tag (a global boolean value) to stop the process.

Thanks

Answer 1

No, that won't run them concurrently - you're waiting for each one to finish before starting the next one.

You could put the results of each Task.Run call into a collection, then await Task.WhenAll after starting them all though.

(It's a shame that Parallel.ForEach doesn't return a Task you could await. There may be a more async-friendly version around...)

Answer 2

This will process the items concurrently.

  Parallel.ForEach(CurrentFeed.Items, DoSomethingAsync)

To be able to cancel you can need a CancellationToken.

  CancellationTokenSource cts = new CancellationTokenSource();
  ParallelOptions po = new ParallelOptions();
  po.CancellationToken = cts.Token;

  // Add the ParallelOptions with the token to the ForEach call
  Parallel.ForEach(CurrentFeed.Items,po ,DoSomethingAsync)

  // set cancel on the token somewhere in the workers to make the loop stop
  cts.Cancel();

For detail see (among other sources) http://msdn.microsoft.com/en-us/library/ee256691.aspx