Add TaskCompletionSource.SetCanceled(CancellationToken)

[Frassle]

TaskCompletionSource currently has three methods to set it to canceled. void SetCanceled() which throws if the source is already completed, bool TrySetCanceled() which just returns false if the source is already cancelled, and bool TrySetCanceled(CancellationToken) which is like TrySetCanceled but also allows linking in a CancellationToken.

Can we also add void SetCanceled(CancellationToken) to use in cases where you want to make it clear that this should set the canceled state but you also want to link a CancellationToken in.
This is doable by writing your own that just throws if TrySetCanceled returns false but this can't easily get the TaskT_TransitionToFinal_AlreadyCompleted resource string to match the error message thrown by corefx. It also leads to people just writing TrySetCanceled and ignoring the result, which leads to less clear code and potentially hides bugs, or alternatively they write SetCanceled and throw away the token information (Me trying to fix one case of this in FSharp.Core is what lead to me raising this issue).

public class TaskCompletionSource<TResult>
{
    ...
    public void SetCanceled(CancellationToken cancellationToken);
    ...
}

[tarekgh]

CC @stephentoub

[stephentoub]

This is reasonable.

[terrajobst]

Video

• Looks good as proposed and follows the guidelines for Try-APIs

public class TaskCompletionSource<TResult>
{
    ...
    public void SetCanceled(CancellationToken cancellationToken);
    ...
}

[stephentoub]

Fixed by #32696