Developers can await a Task with a timeout

[AArnott]

A very popular StackOverflow Q&A asks how to await a Task with a timeout. A simple Task.WithTimeout(TimeSpan) method would alleviate a lot of time developers spend looking for how to properly do this, and avoid doing it wrong (e.g. leaving timers for finalization).

See how we offer a WithTimeout extension method from vs-threading.

[benaadams]

Similar code is already in corefx; but only used for running tests rather than exposed as api

Task TimeoutAfter(this Task task, int millisecondsTimeout)
Task<TResult> TimeoutAfter<TResult>(this Task<TResult> task, int millisecondsTimeout)

https://github.com/dotnet/corefx/blob/407c09d5840384fbd24bbd5b8869ef13be71de63/src/Common/tests/System/Threading/Tasks/TaskTimeoutExtensions.cs#L28-L43

[tarekgh]

CC @stephentoub

[eiriktsarpalis]

I need to use this for production code in #42585, so might as well champion it for API review. Will come up with a proposal shortly.

[eiriktsarpalis]

namespace System.Threading.Tasks
{
    public static class TaskTimeoutExtensions
    {
        // throws TaskCanceledException
        public static Task WithCancellation(this Task task, CancellationToken cancellationToken) => throw null;
        public static Task<TResult> WithCancellation<TResult>(this Task<TResult> task, CancellationToken cancellationToken) => throw null;

        // throws TimeoutException
        public static Task WithTimeout(this Task task, TimeSpan timeout) => throw null;
        public static Task<TResult> WithTimeout<TResult>(this Task<TResult> task, TimeSpan timeout) => throw null;

        public static Task WithTimeout(this Task task, int millisecondsTimeout) => throw null;
        public static Task<TResult> WithTimeout<TResult>(this Task<TResult> task, int millisecondsTimeout) => throw null;
    }
}

I haven't included ValueTask overloads, since it should be straightforward to convert them to task instances.

[pentp]

The comment about throwing TaskCanceledException means that the Task will be marked as canceled, not faulted, right?