在具有超时的同一线程（无线程池）中同步运行任务

Question

I want to use Task<> type, but not with TPL, but with .NET4.5/C#async instead.

Thing is, I have some requirements for my case:

• I want the task to be run synchronously (some people recommend RunSynchronously() , others Wait() , and others ContinueWith(_, TaskContinuationOptions.ExecuteSynchronously) , which one is the adequate here?).
• I want the task to run in the same thread (so, not use the threadpool at all).
• I want the task to stop after a certain timeout has passed, and throw an exception.

For the latter, I think I need Task.Delay() but I'm not sure how to combine it with the first two requirements. Thanks

Answer 1

This answer is based on @svick's comment.

I'm going to make the assumption that you want all the "work" of the method to be done on the same thread as the caller, but that you don't mind if a thread pool thread is used for cancellation purposes (I'm assuming this since you mentioned Task.Delay which will use a Timer which will use a thread pool thread when the timer fires.

That said, there would be no need for Task , since when the method returns you would know for certain that the Task was completed. Just a regular method with a timeout will do:

static void DoSomethingOrThrowAfterTimeout(int millisecondsTimeout)
{
    CancellationTokenSource cts = new CancellationTokenSource(millisecondsTimeout);
    CancellationToken ct = cts.Token;
    // do some work
    ct.ThrowIfCancellationRequested();
    // do more work
    ct.ThrowIfCancellationRequested();
    // repeat until done.
}

Obviously, with this approach of using cooperative cancellation, the method won't timeout exactly at the timeout, as it will be dependent on how small you can split up the work in the method.

If you want to avoid the usage of another thread (for the CancellationTokenSource ), then you could track the starting time and then check how much time has passed (to see if you've exceeded the timeout) at various points in the method (like how ct.ThrowIfCancellationRequested() is used above.