Add a dedicated monitor for graph observer list access - #298
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The observers list was previously only safe because every mutation went through the graph write lock; this adds synchronized(observers) at each access point so it also stays correct if auto-locking is disabled, and marks GraphObserverImpl.destroyed volatile for cross-thread visibility. Adds concurrency tests covering observer create/destroy racing against version-overflow reset and view destruction. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
An independent review found the existing concurrency tests pass even without the observers-monitor fix, since the default auto-locking config already serializes every access via the graph write lock — the monitor only matters when auto-locking is disabled, which nothing exercised. Adds a test under that config, verified to fail (ArrayIndexOutOfBoundsException) on the pre-fix code and pass on it. Also exercises edge-version overflow (previously only node version was covered) and synchronizes a leftover unguarded list read. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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Summary
synchronized(observers)guarding every access point of theGraphStore/GraphViewImplobserver lists (create, destroy,destroyAllObservers, version-reset iteration), so the lists stay correct even whenenableAutoLockingis disabled and the graph's read/write lock is a no-op.GraphObserverImpl.destroyedvolatilefor cross-thread visibility.GraphModelImplis kept as-is: it's what keeps view-existence checks atomic with concurrent view destruction, not just list-mutation safety — removing it (tried during development) reproducibly let an observer get registered on a view that was simultaneously being destroyed.Test plan
testConcurrentCreateAndDestroyGraphObserver(races observer create/destroy against forcedGraphVersionoverflow resets)testConcurrentCreateGraphObserverAndDestroyView(races observer creation againstdestroyView)mvn test— full suite passes (1647 tests, 0 failures)🤖 Generated with Claude Code