Improve detecting subclass of Thread

[zhengyu123]

What does this PR do?:
Improve and simplify detection subclass of Thread

Motivation:
Enhancement.

Additional Notes:

How to test the change?:
Regular CI tests

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a security review (run the dd:platform-security-review
  skill, or file a request via the PSEC review form).
  bewaire also runs automatically on every PR.
• This PR doesn't touch any of that.
• JIRA: PROF-15782

Unsure? Have a question? Request a review!

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR simplifies the logic used to detect whether a run()V method belongs to a Thread type by replacing a manual superclass traversal with a single Class.isAssignableFrom check.

Changes:

• Replaced a java/lang/Class.equals + superclass-walk loop with a call to isAssignableFrom.
• Removed the extra java/lang/Class lookup and related reflection calls.

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[zhengyu123]

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[dd-octo-sts]

✅ All 40 integration tests passed

📊 Dashboard · 👷 Pipeline · 📦 69ce94b8

[dd-octo-sts]

CI Test Results

Run: #32138661798 | Commit: 72de1e7 | Duration: 14m 28s (longest job)

✅ All 32 test jobs passed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
8	-	✅	-	-
8-ibm	-	✅	-	-
8-j9	✅	✅	-	-
8-librca	-	-	✅	✅
8-orcl	-	✅	-	-
11	-	✅	-	-
11-j9	✅	✅	-	-
11-librca	-	-	✅	✅
17	✅	✅	-	-
17-graal	✅	✅	-	-
17-j9	✅	✅	-	-
17-librca	-	-	✅	✅
21	✅	✅	-	-
21-graal	✅	✅	-	-
21-librca	-	-	✅	✅
25	✅	✅	-	-
25-graal	✅	✅	-	-
25-librca	-	-	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 32 | Passed: 32 | Failed: 0

---

Updated: 2026-08-18 13:05:10 UTC

[jbachorik]

LGTM!

[dd-octo-sts]

Scan-Build Report

User:	runner@runnervmzvulz
Working Directory:	/home/runner/work/java-profiler/java-profiler/ddprof-lib/src/test/make
Command Line:	make -j4 all
Clang Version:	Ubuntu clang version 18.1.3 (1ubuntu1)
Date:	Tue Aug 18 12:49:21 2026

Bug Summary

Bug Type	Quantity	Display?
All Bugs	1
Logic error
Dereference of null pointer	1

Reports

Bug Group	Bug Type ▾	File	Function/Method	Line	Path Length
Logic error	Dereference of null pointer	profiler.h	findLibraryByAddress	523	28