如何避免扩展方法中的TaskCanceledException？

Question

I'm starting a Process and wanting to call WaitForExit in an async way. Using another Stack Overflow answer as a template, I have this extension method to do it:

public static class ProcessExtensions
{
    public static Task WaitForExitAsync(this Process process, int milliseconds)
    {
        var tcs = new TaskCompletionSource<object>();
        process.EnableRaisingEvents = true;
        process.Exited += (sender, args) => tcs.TrySetResult(null);

        var cts = new CancellationTokenSource(milliseconds);
        cts.Token.Register(() => tcs.TrySetCanceled());

        return tcs.Task;
    }
}

That way I can call await process.WaitForExitAsync(1000) to accomplish what I want. If the task exits before the timeout happens, then it's all fine. But the problem I'm running into is that when the timeout period is hit, it just throws a TaskCanceledException . The whole point of the extension method is to handle things gracefully in one line. I shouldn't need to wrap this call in a try catch when I just want it to continue either way. How do I accomplish this?

Forgive me for the bad question title, by the way. I couldn't think of how to put this succinctly.

Answer 1

If you want the returned task to be completed successfully, rather than being cancelled, when the token is cancelled, then just call TrySetResult rather than TrySetCancelled when the token is cancelled. You're explicitly telling the TCS to mark the task as cancelled when you call TrySetCancelled .