[ruby-core:112422] [Ruby master Feature#17853] Add Thread#thread_id

Issue #17853 has been updated by Eregon (Benoit Daloze).


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

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Feature #17853: Add Thread#thread_id
https://bugs.ruby-lang.org/issues/17853#change-101870

* Author: komamitsu (Mitsunori Komatsu)
* Status: Closed
* Priority: Normal
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# 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)
```



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