How to use Task.WhenEach in .NET 9


using var tokenSource = new CancellationTokenSource(10_000);
var token = tokenSource.Token;
await foreach (var data in Task.WhenEach(tasks).WithCancellation(token))
{
    if (!tokenSource.TryReset()) 
        token.ThrowIfCancellationRequested();
    Console.WriteLine(await data);
    tokenSource.CancelAfter(10_000);
}

In the preceding code example, CancellationTokenSource is used to create instances of a CancellationToken, which represents a cancellation token to be used for cancellation of a task. The ThrowIfCancellationRquested method is called to throw an OperationCanceledException if cancellation has been requested. The CancelAfter method is used to schedule a cancel operation once the specified number of milliseconds elapses.

Key takeaways

The Task.WhenEach is a new asynchronous static method introduced in .NET 9 that addresses the limitations of the Task.WhenAll and Task.WhenAny methods. By enabling the immediate processing of completed tasks, it enhances the performance and scalability of your applications considerably.

Note that you can use ThrowIfCancellationRequested from within a task only. In this case, you will not have to handle any exception explicitly. Instead, when this method is called on a token instance, the execution leaves the currently running task and the Task.IsCancelled property is set to True.

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