I investigated Python for reference. Current CPython supports threading.get_native_id (https://docs.python.org/3/library/threading.html#threading.get_native_id) which returns native Thread ID.

Implementation details are

• https://github.com/python/cpython/blob/bb3e0c240bc60fe08d332ff5955d54197f79751c/Python/thread_pthread.h#L332-L356
• https://github.com/python/cpython/blob/bb3e0c240bc60fe08d332ff5955d54197f79751c/Python/thread_nt.h#L241-L252

This method can be used as below

# cat thread.py import threading import time import os def p(): while True: print(threading.get_native_id()) time.sleep(1) print(os.getpid()) thread1 = threading.Thread(target=p) thread2 = threading.Thread(target=p) thread1.start() thread2.start() thread1.join() thread2.join() 

# python thread.py 15 # <- pid 16 # <- Thread id 17 # <- Thread id # ps -efL UID PID PPID LWP C NLWP STIME TTY TIME CMD root 1 0 1 0 1 07:28 pts/0 00:00:00 /bin/bash root 9 0 9 0 1 07:29 pts/1 00:00:00 /bin/bash root 15 1 15 0 3 07:30 pts/0 00:00:00 python thread.py root 15 1 16 0 3 07:30 pts/0 00:00:00 python thread.py root 15 1 17 0 3 07:30 pts/0 00:00:00 python thread.py root 19 9 19 0 1 07:30 pts/1 00:00:00 ps -efL 

+1 This would be useful for Datadog's ddtrace gem as well: currently we need to do quite a bit of hackery and monkey-patching to get the per-thread cpu clock information, and if we had the native id, we could use that instead to call Process.clock_gettime.

Two concerns.

(1) name should include native, os or something to represent it is platform value. Maybe native_id same as Python's API is enough. Ruby can set internal ID for threads.
(2) In future the thread model can be changed (1:1 -> M:N). In this case, native_id should be changed (or nil if the ruby thread is not running on native thread).

native_id sounds better to me. I agree with it.

As for m:n thread model, in my opinion, either volatile value or nil (this can happen when it's waiting an event in select/epoll/kqueue without assigning any thread?) sounds good to me since what I want to do is just mapping the result of Ruby Thread information to native thread resource. current_native_id might be better since it sounds like the attribute/property can be easily changed.

Created a proposed implementation:
https://github.com/ruby/ruby/compare/master...nurse:native_thread_id

Thanks a lot for building this, @naruse (Yui NARUSE)!

If I can ask for a tiny addition, it would be really cool to get the native_thread_id, if available, in Thread#inspect :)

diff --git i/thread.c w/thread.c index cbef44a9d4a..c627e5c8f2a 100644 --- i/thread.c +++ w/thread.c @@ -3456,6 +3456,14 @@ rb_thread_to_s(VALUE thread) if (!NIL_P(target_th->name)) { rb_str_catf(str, "@%"PRIsVALUE, target_th->name); } +#if USE_NATIVE_THREAD_NATIVE_THREAD_ID + if (!rb_threadptr_dead(target_th)) { + VALUE native_id = native_thread_native_thread_id(target_th); + if (!NIL_P(native_id)) { + rb_str_catf(str, "(%"PRIsVALUE")", native_id); + } + } +#endif  if ((loc = threadptr_invoke_proc_location(target_th)) != Qnil) { rb_str_catf(str, " %"PRIsVALUE":%"PRIsVALUE, RARRAY_AREF(loc, 0), RARRAY_AREF(loc, 1)); 

@nobu (Nobuyoshi Nakada) that looks great!

Thank you, @naruse (Yui NARUSE) and @nobu (Nobuyoshi Nakada)!

FWIW, it seems the Thread#inspect change wasn't merged.