Why I can't get the ProcessorAffinity of a thread?

Question

I'm making a program for CPU usage statistics. I have a list of Processes, each one with its Process.Threads. For each thread, I want to know its current affinity to know which CPU Core it is binded to, but ProcessThread.ProcessAffinity can only be set... not read!

Why? Is there a way to get this information?

Moreover, can I get it without calling low-level Win32 functions but just .NET Standards?

Answer 1

After the hint by @oliver-rogier, I've managed to do it by using the function to Set the mask (imported from C++). As explained in the docs:

Return value

If the function succeeds, the return value is the thread's previous affinity mask.

[DllImport(@"kernel32.dll", SetLastError = true)]
static extern IntPtr SetThreadAffinityMask(IntPtr hThread, IntPtr dwThreadAffinityMask);


public static IntPtr GetThreadAffinityMask(uint threadId)
{
    Thread.BeginThreadAffinity();

    // get the handle
    IntPtr hThread = OpenThread(ThreadAccess.SET_INFORMATION | ThreadAccess.QUERY_INFORMATION, false, threadId);
    if (hThread == INVALID_HANDLE_VALUE)
    {
        var err = GetLastError();
        return IntPtr.Zero;
    }

    // there is no "get" for affinity mask, but the "set" function returns the mask before the operation
    // so first set a temp mask to obtain the current one
    IntPtr old = SetThreadAffinityMask(hThread, new IntPtr((int)Math.Pow(2, Environment.ProcessorCount)) - 1);
    if (old == IntPtr.Zero)
    {
        var err = GetLastError();
        return old;
    }

    // then restore the original value
    SetThreadAffinityMask(hThread, old);

    CloseHandle(hThread);
    Thread.EndThreadAffinity();

    return old;
}