CODEWITHSUNDEEP
c#multithreadingcontinuewith
lilo0
lilo0

Reputation: 1035

Task continuation unexpected behaviour

please take a look at the following code:

So, I grab the current context (WinForms thread), start a new task with that context, and attach a synchonous continuation with the Default task scheduler. As far as I understand, a continuation should start on a threadpool thread. UI thread doesn't belong to threadpool. But instead, all code including a continuation, is running synchonously on the same thread. That's quite unexpected for me.

Btw, if I set the continuation options as TaskContinuationOptions.None, it's run on another thread as it should. Seems like continuation options make preference over task scheduler, despite they are just hints and scheduler is a requirement.

TaskScheduler uiContext = TaskScheduler.FromCurrentSynchronizationContext();
Console.WriteLine("start thread {0}", Thread.CurrentThread.ManagedThreadId);

Task.Factory.StartNew(() =>
{
    Console.WriteLine("ui thread {0}", Thread.CurrentThread.ManagedThreadId);
}, CancellationToken.None, TaskCreationOptions.None, uiContext).ContinueWith(t =>
{
    Console.WriteLine("continuation thread {0}", Thread.CurrentThread.ManagedThreadId);
}, CancellationToken.None, TaskContinuationOptions.ExecuteSynchronously, TaskScheduler.Default);

Is it a bug or expected behaviour?

What can I do to guaranteed run of the continuation code outside of UI thread independently of the parent task context and continuation options? Some custom task scheduler?

A note: I know this is a legacy code now, and async/await is the way to go.

Upvotes: 1

Views: 68

Answers (0)

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