Feature #17853: Add Thread#thread_id

• Status: Closed
• Assignee: -
• Target version: -

[komamitsu (Mitsunori Komatsu)]

Abstract

New method Thread#thread_id to get associated native thread id (LWP.) It might return nil if OS doesn't support thread id or equivalent.

Background

When I tried to investigate which Ruby thread of an application is busy, I did the following steps

• checked the CPU usage of the Ruby application's threads using ps -eLf or top (with H key) and got which thread is busy
• dumped all the threads of the application using https://github.com/frsyuki/sigdump
• tried to find a busy thread in the thread dump result, but the thread dump doesn't contain thread id...

Thread class itself has no method to get associated thread id. If the class has #thread_id or something, I can create a PR on sigdump project to add thread id in thread dump output to make investigations with thread dump much easier.

Thread#name may seem an alternative to Thread#thread_id, but Thread#name just returns a value that's set through Thread#name= while Thread#thread_id returns a thread id that OS or something has assigned.

In case of Java, thread dump created by jcmd ${pid} Thread.print contains nid field which is an associated native thread id

"http-bio-80-exec-77" daemon prio=6 tid=0x0000000026f29000 nid=0xbd0 runnable [0x0000000020c7f000]
   java.lang.Thread.State: RUNNABLE
    at java.net.SocketInputStream.socketRead0(Native Method)
    at java.net.SocketInputStream.read(Unknown Source)
    at java.net.SocketInputStream.read(Unknown Source)
    at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:516)
    at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:501)
    at org.apache.coyote.http11.Http11Processor.setRequestLineReadTimeout(Http11Processor.java:167)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:946)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
    - locked <0x00000007b16e3e88> (a org.apache.tomcat.util.net.SocketWrapper)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

[naruse (Yui NARUSE)]

• Related to Feature #11251: Thread#name and Thread#name= added

[komamitsu (Mitsunori Komatsu)]

• Description updated (diff)

[komamitsu (Mitsunori Komatsu)]

• Description updated (diff)

[yui-knk (Kaneko Yuichiro)]

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

[ivoanjo (Ivo Anjo)]

+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.

[ko1 (Koichi Sasada)]

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).

[komamitsu (Mitsunori Komatsu)]

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.

[naruse (Yui NARUSE)]

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

[naruse (Yui NARUSE)]

• Status changed from Open to Closed

Applied in changeset git|46655156dcc37509dcb69fcd0717c110eb1c624a.

---

Add Thread#native_thread_id [Feature #17853]

[ivoanjo (Ivo Anjo)]

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 :)

[nobu (Nobuyoshi Nakada)]

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));

[ivoanjo (Ivo Anjo)]

@nobu (Nobuyoshi Nakada) that looks great!

[komamitsu (Mitsunori Komatsu)]

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

[Eregon (Benoit Daloze)]

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