Avoid repeated reachability walks while Moose modules initialize

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35/100
Issue-Typ
Bug
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java
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compilers

Rechercherichtung

Start in WeakRefRegistry.weaken(), at the weakenedLiveBlessedRef condition, where reachableOwnerCount() is evaluated before ModuleInitGuard.inModuleInit(). Follow reachableOwnerCount() into ReachabilityWalker.isScalarReachable() to see the root walk. Reorder the check, add a deterministic regression test for module initialization, and confirm weak-reference behaviour outside module init. Done when t/05_round.t finishes on both the JVM and interpreter backends.

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Beschreibung

area:memory area:performance bug

Summary

Loading StorageDisplay 1.0.11 through Moose triggers a large number of Scalar::Util::weaken calls. For live blessed references, WeakRefRegistry.weaken() calls reachableOwnerCount(), which repeatedly walks the Perl object graph. The module-initialization guard is checked only after this expensive query, so it does not suppress the work during module loading. The repeated walks make t/05_round.t exceed the CPAN tester timeout on both PerlOnJava backends.

Evidence

  • CPAN random tester run: 20261102-094403-98885
  • Distribution: StorageDisplay-1.0.11; failing test: t/05_round.t
  • System Perl 5.42.2: full suite passed, 7 files / 85 tests, in about 6 seconds.
  • PerlOnJava 5.44.1 / Java 24.0.2: CPAN run timed out after 120 seconds with no output for 60 seconds. Focused runs of t/05_round.t with the archived dependency overlay exceeded a 40-second hard timeout on both JVM and interpreter backends.
  • An 8-second JVM Flight Recorder profile of use StorageDisplay showed repeated stacks through ScalarUtil.weaken, RuntimeBase.reachableOwnerCount, and ReachabilityWalker root traversal. This is repeated work, not evidence of an infinite loop.

StorageDisplay is pure Perl and uses Moose 2.4000 and namespace::sweep 0.006. The PerlOnJava report showed t/000-report-versions.t passing before the harness stopped producing output.

Suspected cause

In WeakRefRegistry.weaken(), the condition at the weakenedLiveBlessedRef check evaluates base.reachableOwnerCount() == 0 before !ModuleInitGuard.inModuleInit(). reachableOwnerCount() checks each active owner using ReachabilityWalker.isScalarReachable(), which traverses the global root graph. Moose performs many such weaken operations while required modules execute under ModuleInitGuard, multiplying full root walks during initialization.

Move the module-init check ahead of the reachability query, then confirm the same behavior is preserved outside module initialization.

Acceptance criteria

  • Add deterministic regression coverage proving module initialization does not perform the expensive reachable-owner walk for this path.
  • Run new/changed Perl-level coverage with system Perl first.
  • t/05_round.t completes under PerlOnJava's JVM and interpreter backends with the archived dependency load order.
  • Run the required build and lifecycle tests; retain bounded output and verify weak-reference semantics outside module initialization.

Related: #1642 and merged PR #1746 addressed other repeated reachability paths during cleanup. This CPAN case reproduces through WeakRefRegistry.weaken() during module initialization.

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Perl
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Gemergte PRs (30 T.)
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