Timeout pattern on task-based asynchronous method in C#

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While you can reuse WithCancellation for both cancellations and timeouts I think it’s an overkill for what you need.

A simpler and clearer solution for an async operation timeout would be to await both the actual operation and a timeout task using Task.WhenAny. If the timeout task completes first, you got yourself a timeout. Otherwise, the operation completed successfully:

public static async Task<TResult> WithTimeout<TResult>(this Task<TResult> task, TimeSpan timeout)
{
    if (task == await Task.WhenAny(task, Task.Delay(timeout)))
    {
        return await task;
    }
    throw new TimeoutException();
}

Usage:

try
{
    await DoStuffAsync().WithTimeout(TimeSpan.FromSeconds(5));
}
catch (TimeoutException)
{
    // Handle timeout.
}

If you prefer to not throw an exception (as I do) it’s even simpler, just return the default value:

public static Task<TResult> WithTimeout<TResult>(this Task<TResult> task, TimeSpan timeout)
{
    var timeoutTask = Task.Delay(timeout).ContinueWith(_ => default(TResult), TaskContinuationOptions.ExecuteSynchronously);
    return Task.WhenAny(task, timeoutTask).Unwrap();
}

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