How to get KernelID in from KernelObject?

Question

In a nutshell, how can I get this number:

I'm having trouble because $KernelID isn't a function and the FullForm is this crazy thing:

Motivation:

After you call CloseKernels[], the next time you LaunchKernels[] the new kernels don't start from one again:

In my parallel code I'd like to have access to the index of the kernel from 1 to $KernelCount, but I'm not sure how to efficiently get that:

offset = ToExpression@(StringCases[ToString[Kernels[][[1]]], NumberString][[1]])
(*Out[]= 17*)

Answer 1

You can use the internal, undocumented function Parallel`Developer`KernelID to do this:

LaunchKernels[3];
Parallel`Developer`KernelID /@ Kernels[]

{1, 2, 3}

Close kernels and try again:

CloseKernels[];
LaunchKernels[4];
Parallel`Developer`KernelID /@ Kernels[]

{4, 5, 6, 7}