Question

is it possible to run some of my PLINQ AsParallel() – Queries with a lower priority than others?
(Or some with a higher priority than others)
Is this possible with PLinq or will I have to avoid PLINQ and do all the stuff on my own?

EDIT/UPDATE:

Would it be possible to call

Thread.Sleep(0)

inside the parallel executed method when I want to archive a lower priority?
Or is that a very bad practice/hack?

Answer 1

Unfortunately, this is not directly possible in PLINQ.

You can do it in most of the rest of the Task Parallel Library via creation of a custom TaskScheduler. This would allow you to have custom "priorities" when using Parallel.For or ForEach.

However, the ability to customize the TaskScheduler was not provided with PLINQ, since PLINQ requires very strict guarantees from the TaskScheduler, and the fear was that exposing this would be very problematic.

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EDIT/UPDATE:

Would it be possible to call

Thread.Sleep(0)

This would "lower" the priority, but unfortunately, has it’s own issues, especially when combined with PLINQ. This will potentially cause thread starvation in the ThreadPool, since you’ll be "sleeping" on ThreadPool threads.

In addition, there’s a fundamental problem with this – PLINQ is designed and intended to handle queries, and is not designed for processing. Introducing logical code to control the flow structure is really against the theory behind PLINQ, and will likely cause unintended performance repercussions you aren’t expecting, especially if you’re using the default partitioning.