C# get results from Task.WhenAll

The C# method Task.WhenAll can run a bunch of async methods in parallel and returns when every one finished.

But how do you collect the return values?

Imagine that you have this pseudo-async-method:

private async Task<string> GetAsync(int number)
  return DoMagic();

And you wish to call that method 20 times, and then collect all the results in a list?

That is a 3 step rocket:

  1. Create a list of tasks to run
  2. Run the tasks in parallel using Task.WhenAll.
  3. Collect the results in a list
// Create a list of tasks to run
List<Task> tasks = new List<Task>();
foreach (int i=0;i<20;i++)

// Run the tasks in parallel, and
// wait until all have been run
await Task.WhenAll(tasks);

// Get the values from the tasks
// and put them in a list
List<string> results = new List<string>();
foreach (var task in tasks)
  var result = ((Task<string>)task).Result;



About briancaos

Developer at Pentia A/S since 2003. Have developed Web Applications using Sitecore Since Sitecore 4.1.
This entry was posted in General .NET. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.