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Avoid repeated live-root scans over growing lexical aggregates

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Avaliação

Dificuldade
4/5
Tempo estimado
3-5 dias
Facilidade para iniciantes
52/100
Tipo de issue
Bug
Clareza
Razoavelmente clara
Status de atividade
Ativa
Stack de tecnologia
java, perl
Domínio
operating-systems, performance

Direção de pesquisa

Start with the reachability tests and the cleanup path around ReachabilityWalker.LiveRootSnapshot.build(), identified by the profiling evidence; inspect the regression work in #1642 for context. Add deterministic coverage that counts snapshot traversal while a lexical root graph grows, preserving weak-reference, scope-exit, and root-mutation behavior. Run the Perl-level test with system Perl, then verify both PerlOnJava backends and the unchanged Data-Tumbler-0.010 stress test.

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Descrição

area:memory area:performance area:runtime bug

Summary

Data-Tumbler 0.010's t/90-stress.t times out under PerlOnJava although the complete upstream suite passes under system Perl. The stress test emits 4^8 (65,536) leaves and appends each result to a lexical output array.

Evidence

  • CPAN random-tester regression run: 20261021-223510-14962.
  • System Perl 5.42.2, Temurin Java 24.0.2, macOS arm64.
  • System Perl: PASS, 4 files / 5 tests; the stress test completes in under one second.
  • PerlOnJava at parent 8bc1c9d1708de1381be6c042d6530c0c318e24f4: t/00-basic.t, t/10-simple.t, and t/20-examples.t pass, then the harness produces no output and exceeds its 120-second soft limit while running the stress test.
  • Reproduction on both PerlOnJava backends: 4^8 exceeds 180 seconds on JVM and 60 seconds on interpreter. On JVM, 4^6 takes 1.2 seconds and 4^7 takes 38.8 seconds, showing a sharp superlinear increase.
  • JFR samples identify ReachabilityWalker.LiveRootSnapshot.build() and its traversal as a major hot path during deferred aggregate cleanup. The stress test's lexical output array grows with every leaf, so repeated live-root snapshots revisit an increasingly large graph.
  • Data::Tumbler is pure Perl and requires no native library, service, or display. This is related to the root-walk performance work in #1642, but this reproduction exercises repeated live lexical snapshots over a growing output graph after that fix.

Acceptance criteria

  • Add deterministic regression coverage for repeated cleanup while a lexical root graph grows; assert bounded snapshot traversal work rather than elapsed time.
  • Preserve weak-reference, scope-exit, and root-mutation semantics covered by the existing reachability tests.
  • Run the new Perl-level test with system Perl, then verify JVM and interpreter behavior.
  • The unchanged Data-Tumbler-0.010 stress test completes on both PerlOnJava backends without the observed superlinear slowdown.
Linguagem predominante
Perl
Estrelas
64
Forks
8
Merge médio
5h 42min
PRs com merge (30d)
205

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