native_thread_id

        # Thread.native_thread_id

(from ruby core)
---
    thr.native_thread_id   -> integer

---

Return the native thread ID which is used by the Ruby thread.

The ID depends on the OS. (not POSIX thread ID returned by
pthread_self(3))
*   On Linux it is TID returned by gettid(2).
*   On macOS it is the system-wide unique integral ID of thread returned
    by pthread_threadid_np(3).
*   On FreeBSD it is the unique integral ID of the thread returned by
    pthread_getthreadid_np(3).
*   On Windows it is the thread identifier returned by GetThreadId().
*   On other platforms, it raises NotImplementedError.


NOTE: If the thread is not associated yet or already deassociated with a
native thread, it returns *nil*. If the Ruby implementation uses M:N
thread model, the ID may change depending on the timing.