fix(chaos): rate-limit tight-loop antagonists to prevent long-run OOM

[jbachorik]

What does this PR do?:
Adds inter-iteration sleeps to three chaos antagonists that ran in tight loops without yielding, causing Java heap OOM after ~1 hour in the scheduled reliability/chaos CI cell.

Motivation:
The chaos harness was failing with java.lang.OutOfMemoryError: Java heap space after ~59 minutes. Root cause: WeakRefWaveAntagonist.waveLoop() calls System.gc() in a tight loop with no pause between waves. Each forced full-GC is a stop-the-world pause during which ThreadChurnAntagonist (64 threads/5ms), DumpStormAntagonist (96 threads), and AllocStormAntagonist keep accumulating objects. Over time this degrades into GC thrashing and exhausts the 2GB heap.

Two secondary contributors also ran with no inter-iteration sleep: ClassLoaderChurnAntagonist and HiddenClassChurnAntagonist both define unique classes in tight loops; ClassLoaders require old-gen GC to collect and can accumulate faster than the GC can reclaim them.

Changes:

• WeakRefWaveAntagonist: 200ms sleep after each wave — gives G1's concurrent markers time to work between forced full GCs
• ClassLoaderChurnAntagonist: 1ms sleep per iteration — enough for old-gen to keep up with ClassLoader churn
• HiddenClassChurnAntagonist: 1ms sleep per iteration — same reason

The System.gc() call is preserved; only the pathological back-to-back cadence is fixed.

Additional Notes:
No profiler code changed. This is purely a chaos harness fix.

How to test the change?:
The scheduled reliability/chaos CI pipeline will exercise this. The harness should now complete the full duration (RUNTIME seconds) without OOM.

For Datadog employees:

• This PR doesn't touch any of that.
• JIRA: N/A — no ticket, direct chaos harness fix

[dd-octo-sts]

CI Test Results

Run: #27750860542 | Commit: e37755c | Duration: 12m 59s (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: 2026-06-18 10:00:54 UTC

[datadog-datadog-prod-us1-2]

✨ Fix all issues with BitsAI

⚠️ Warnings

🚦 14 Pipeline jobs failed

DataDog/java-profiler | benchmarks-candidate-aarch64: [alloc]     

DataDog/java-profiler | benchmarks-candidate-aarch64: [cpu,wall,alloc,memleak]     

DataDog/java-profiler | benchmarks-candidate-aarch64: [cpu,wall]     

View all 14 failed jobs.

Useful? React with 👍 / 👎

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: a83ec01 | Docs | Datadog PR Page | Give us feedback!}

[rkennke]

Yup makes sense, and looks good!

[jbachorik]

@rkennke thanks for the review!