Mechanisms for Creating Tasks

re: Mechanisms for Creating Tasks

Abhijeet Patel — Wed, 01 Jul 2009 07:24:29 GMT

Hi Stephen:

re:"_" is a valid identifier name.

Right...I guess I'm just used to seeing alphabetic identifiers in general and hence the "_" threw me off,come to think of it "_xxx" is a common naming convention for private data members but I never realized(nor have ever used ) "_" by itself as an identifier.

Thanks for the clarification.

re: Mechanisms for Creating Tasks

Stephen Toub - MSFT — Tue, 30 Jun 2009 10:10:48 GMT

Hi Abhijeet-

re: is this correct?

Oops, no, it was a typo. Should have been "t.ContinueWith" rather than "timer.ContinueWith". I fixed it in the post. Thanks.

re: is this just pseudocode or valid C#

In C#, "_" is a valid identifier name. Since my delegate doesn't need the parameter that's passed in, I've used an "_" to signify that I don't care about it.

re: Mechanisms for Creating Tasks

Abhijeet Patel — Tue, 30 Jun 2009 09:42:22 GMT

In your first code sample, you have a ContinueWith on the Timer object, is this correct?

Also, not sure what the underscore means, is this just pseudocode or valid c#?

var timer = new Timer(

_ => t.Start(), null, millisecondsDelay, Timeout.Infinite);

timer.ContinueWith(_ => timer.Dispose());

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re: Mechanisms for Creating Tasks

Stephen Toub - MSFT — Thu, 18 Jun 2009 02:35:55 GMT

Hi James-

The June 2008 CTP does have ContinueWith methods on Task, so you should be able to use them there.

The bits have changed significantly since incorporation into .NET 4, so if you can install the .NET Framework 4 Beta, that'll be your best bet for playing with recent bits.

http://msdn.microsoft.com/en-us/vstudio/dd582936.aspx

re: Mechanisms for Creating Tasks

James B — Wed, 17 Jun 2009 20:34:52 GMT

You mention "Task also exposes a ContinueWith mechanism that can be used to create a Task that will be scheduled when the antecedent task (the Task on which ContinueWith is being called) completes.", which I see here:

http://msdn.microsoft.com/en-us/library/dd321262(VS.100).aspx

However, I do not see anything like this in the June 2008 CTP. Am I correct in thinking it is missing? If so, is there anywhere I can get a more modern library, usable outside a VS2010 VM?

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re: Mechanisms for Creating Tasks

Eric Eilebrecht - MSFT — Sat, 06 Jun 2009 17:57:44 GMT

Timer works by registering itself with the ThreadPool, which inserts the timer in a list of active timers. The ThreadPool maintains a separate "timer thread" which calls Sleep() with the duration of the timer that will fire next. Offloading the Sleep to this special thread has two benefits: first, it frees the worker thread to execute other tasks, and second it allows multiple timers to be processed by a single thread. So instead of tying up 10 threads with 10 calls to Thread.Sleep, you have a single thread handling all 10 timers. As each timer fires, the callback is queued back to the worker pool, freeing up the timer thread to process the rest of the timers.

re: Mechanisms for Creating Tasks

aL — Sat, 06 Jun 2009 14:44:34 GMT

ah i see.. so it does sort of what Timer does but on the OS thread level instead of the Task level? it'd be interesting to hear more about how Timer does its thing :) does it talk to the threadpool directly and asks not to be scheduled until the time has passed? how does it do that? with an internal api?

sorry, lots of questions.. but the tpl is very interesting stuff :)