Flaky test: AllocationMetricCollectorTest.testDelta #20455

This issue was generated automatically by Claude Code (Anthropic's AI coding agent) running a scheduled CI-triage routine on behalf of @FrankChen021. Analysis and suggested fixes are AI-produced; please verify before acting on them.

Status: Resolved by #20457
Subject: AllocationMetricCollectorTest.testDelta (processing, unit tests (25, M*,A*,V*,W*))
Failures: 2 · First seen: 2026-09-29 · Last seen: 2026-09-30

Root cause

Line 61 asserts that the summed per-thread allocation delta exceeds threads * 100000 * 16 bytes. The test assumes every new Object() in the worker loop is heap-allocated at 16 bytes. The list holding them is never read, so once the lambda is hot, C2 escape analysis can scalar-replace those allocations. The bound then fails, and it keeps failing on in-fork reruns because the code is already JIT-compiled. The failing commit (#20310) only changes StringUtils charset handling, and the test passed on the other six master runs that day, including the next commit.

Suggested fix

Make the allocations observable: publish each worker's list to a shared volatile field or collection, or allocate byte[] of known size and keep a reference. Also assert against a conservative fraction of the expected size rather than an exact lower bound. #20457 (merged 2026-10-01) retains the allocations.

Occurrences

Failed push-triggered master jobs only. The daily triage routine adds one row per new failed job.