Second hotfix attempt for the "ball of spikes" terrain corruption.
The previous _datLock fix was insufficient because dat reads happen
from many render-thread code paths I didn't enumerate (animation
tick, OnLiveMotionUpdated, OnLivePositionUpdated, the live spawn
hydration, ApplyLoadedTerrain) and locking each is invasive and
fragile.
DatReaderWriter's DatCollection is fundamentally not thread-safe:
DatBinReader's internal buffer position is shared per-database, so
two concurrent .Get<T> calls corrupt each other's read state. The
ArgumentOutOfRangeException at DatBinReader.ReadBytesInternal in
the failure log is the smoking gun — one read started reading a
LandBlock, another moved the reader's position, the first one
asked for the wrong number of bytes.
Until Phase A.3 introduces a thread-safe dat wrapper (or until we
preload all dats into pure in-memory dictionaries), the streamer
runs synchronously: EnqueueLoad invokes the load delegate inline
on the calling thread and writes the result to the outbox in a
single call. The render-thread DrainCompletions loop picks it up
on the same frame.
API surface unchanged — Channel-based outbox, EnqueueLoad/Unload,
DrainCompletions, Start (now no-op), Dispose all preserved. Move
back to async loading is a single-class change once dat thread
safety lands.
Cost: visible frame hitch when crossing landblock boundaries
(rendering the new landblock is now on the render thread). For
default 5×5 the hitch is one landblock per cardinal step, ~50ms
worst case. Acceptable for the MVP — correctness over hitches.
Updated the off-thread test to assert the new synchronous contract
(loader runs on the calling thread). The other 4 tests still pass
unchanged because their spin-drain pattern works with synchronous
delivery too.
The previous _datLock from commit c991fb2 stays in place as
defensive belt-and-suspenders — it's free in synchronous mode and
keeps the contract documented at every dat-reading entry point.
212 tests green.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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