Ludovic Marie
51 lines
3.1 KiB
Markdown
51 lines
3.1 KiB
Markdown
# Release a blocked terrain read during shutdown
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A local world test saved its chunks and closed the DH databases, then hit the
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client shutdown watchdog. Its remaining non-daemon DH world-generation worker
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was waiting in `IOWorker.isOldChunkAround` on a cached blending-metadata future.
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The unchanged control exited normally, so the failure is intermittent; this
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observation does not attribute it to the culling optimization.
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The scoped redirect uses an interruptible wait only for pending blending reads
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on threads named `DH-World Gen Thread[...]`. The pinned DH 3.3.4 pool uses this
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name and interrupts remaining workers during shutdown. Ordinary Minecraft
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callers keep `CompletableFuture.join` behavior. Completed results use the original
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join path. Failed reads retain join's exception identity and wrapping behavior.
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An interrupted DH waiter restores its interrupt flag and throws a completion
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exception whose interrupted cause is recognized by DH's existing shutdown
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handling. It never cancels or completes the cached future, which belongs to other
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callers too. Chunk stores, saves, storage closure and world difficulty are untouched.
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This changes cancellation of an interrupted background task, rather than terrain
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results from an uninterrupted task.
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Profiles with distant terrain request the fix; baseline and low-memory profiles
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without DH do not. It is restricted to Minecraft 26.3 and DH 3.3.4. To opt out,
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set `enabled=false` in `config/horizon-terrain-read-wait.properties` and restart.
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Frame reports record `interruptible_terrain_read`, and comparison tools disclose
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changes in that state.
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`python tools/test_terrain_read.py` checks the actual transformed game IOWorker
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inside Fabric, with controlled cached metadata futures. It forces an interrupted
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pending DH read, verifies the shared future remains available to a later caller,
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and checks that ordinary callers remain blocked until completion. It also
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checks an interrupt already set before a pending read, successful completed
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reads with an interrupt already set, cancelled
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futures, exceptional completion identity, and recognition by DH's shutdown
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exception utility. The private fixture does not enter release packs. This is a
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correctness check, not an FPS, throughput or Mac shutdown benchmark.
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The [sanitized Linux CI result](../benchmarks/terrain-read-2026-10-04/linux-applied-hooks.json)
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includes source/workflow provenance and the original mod checksum. The CI JAR
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matches the local candidate byte-for-byte. Windows and hosted Apple Silicon
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macOS 26 compile the fixture and pass the portable build/metrics checks; applied
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read interruption is exercised on Linux, not a live macOS game.
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The exact candidate also completed a 120-second local world recording, saved,
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and reloaded that world in the same client. After the first save, thread inspection
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found no remaining DH generation workers and no background workers blocked on a
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future. After reload, two generation workers existed and neither was waiting in
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blending metadata; no background metadata-scan wait was present at that snapshot.
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This is one software-rendered lifecycle observation, not proof that every
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shutdown race, world or platform is covered.
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