[RESOLVED] Core Affinity

[PlausiblyDamp]

Yeah, all that's true or likely so. Having more threads than there are cores, defeats the purpose....and now that I think about it, I might have more cores on this system than I thought. I was thinking I had four, but six would be more likely. I'll have to look at some point.

My understanding of Tasks was that they were lighter weight than creating full threads, and would be managed by the OS to only start up when there was a core free to work on. That's not what is happening, based on what I am seeing, unless they are all on the same core...which looks likely. In that case, using Tasks in the way I was doing was essentially the same as running each one sequentially, with the added overhead of Task management.

I have realized that there is a much better way to do this, which splits the work up more meaningfully, but I'm reluctant to try it, because it would mean that some of the nicer features of the UI would be rendered meaningless. Therefore, I think I won't change it. The time taken is not too steep a price to pay for having a nice UI.

IIRC Tasks are delegated to the ThreadPool when created using Task.Run - this allows the ThreadPool itself to balance the number of running threads.

If you run the following Console app

Imports System.Runtime.InteropServices

Module Program

       Sub Main()

        Dim tasks As New List(Of Task)
        For i = 0 To 100
            Dim x = i
            tasks.Add(Task.Run(Sub() DoStuff(x)))
        Next

        Task.WaitAll(tasks.ToArray)

    End Sub

    Private Async Sub DoStuff(i As Integer)
        Console.WriteLine($"Starting Task {i} on Thread {Environment.CurrentManagedThreadId}, on cpu {GetCurrentProcessorNumber()}, {ThreadPool.PendingWorkItemCount()} Items queued")
        Task.Delay(5000).Wait()
        Console.WriteLine($"Ending Task {i} on Thread {Environment.CurrentManagedThreadId}, on cpu {GetCurrentProcessorNumber()}, {ThreadPool.PendingWorkItemCount()} Items queued")

    End Sub


    <DllImport("Kernel32.dll")>
    Public Function GetCurrentProcessorNumber() As Integer
    End Function

End Module

You will see the output creates multiple tasks, some using the same thread, and the threads are using different cpus / cores. Note that a thread may also move between cores.