TaskFactory.StartNew versus ThreadPool.QueueUserWorkItem
Apparently the TaskFactory.StartNew method in .NET 4.0 is intended as a replacement for ThreadPool.QueueUserWorkItem (according to this post, anyway). My question is simple: does anyone know why?
Does TaskFactory.StartNew have better performance? Does it use less memory? Or is it mainly for the additional functionality provided by the Task class? In the latter case, does StartNew possibly have worse performance than QueueUserWorkItem?
It seems to me that StartNew would actually potentially use more memory than QueueUserWorkItem, since it returns a Task object with every call and I would expect that to result in more memory allocation.
In any case, I'm interested to know which is more appropriate for a high-performance scenario.
Answer
Performance is a ... depends. If you are doing a lot of parallel tasks, then .net 4 tasks will perform better, plus give you more fine grained control (more robust cancellation, ability to wait on multiple tasks simultaneously, ability to create parent/child task relationships, Ability to specify LongRunning, etc.. etc.. etc..)
Additionally, the ability to specify your own TaskScheduler means you can customize it for your needs. The built-in task scheduler is far more multi-core aware than the old ThreadPool.
As for using more memory. Every thread reserves a minimum of 1MB of memory, the tiny amount used to store a task object is inconsequential. I really would think that's the last of your worries.