feat(ucxx): single-chunk transfer + health-aware client rotation#695
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Add Slurm CI tooling and harden replica teardown so test_process_flow no longer hangs for hours: fail-fast Redis stream polls during shutdown, controller finalize on heartbeat-death reap (with a startup guard so SFT controllers do not self-destruct before workers register), bounded HTTP timeouts, teardown progress logging, and a bounded test-side wait with faulthandler diagnostics.
Reworks the UCXX payload transport for correctness and
simplicity, and removes a deprecated trainer-side mixin.
**Wire protocol (single chunk per slot).** One connection, one
``send([slot])``, one ``recv(status)``, one ``recv(payload)``.
The handler that performs the slot's ``READY -> READING``
transition is the unique owner of its
``READING -> {FREE | READY}`` finalisation for that read
attempt. No refcounting, no shared cross-handler state, no
multi-chunk fan-out.
**Two structural invariants** make orphan handlers harmless:
1. *Defensive slot-state transitions.*
``SharedRingBuffer.mark_consumed`` and ``release_reading``
no-op (with a warning) on unexpected slot states instead of
clobbering them. A late finalise from an orphan handler --
e.g. one still mid-``send`` after the client rotated to a
different port -- cannot silently undo a writer's recycle.
2. *Single owner per read attempt.* Each handler calls exactly
one of ``mark_consumed`` (success) or ``release_reading``
(failure) in its ``finally`` block.
**Three-layer client retry stack.**
* ``UCXXClient.read``: per-call port rotation with on-timeout
fallback, plus a per-port skip-list so ports that have just
produced ``UCXXConnectionResetError`` /
``UCXXMessageTruncated`` / timeout are quarantined for
``_PORT_QUARANTINE_SEC`` and skipped on subsequent calls
while at least one healthy port remains.
* ``UCXXDataPackerMixin._read_one``: per-slot fresh-call retry,
with ``StaleSlotError`` flagged non-retryable so a recycled
slot is not re-fetched in the same batch.
* ``UCXXDataPackerMixin._ucxx_dp_fetch_all``: multi-round batch
retry (``_MAX_FETCH_ROUNDS``).
**Audit-pass fixes.**
* Stop server-thread busy-spin: shutdown watchdog now sleeps
for 50 ms instead of yielding via ``asyncio.sleep(0)``.
* ``SharedRingBuffer.get_ready_count`` actually counts
``READY`` slots instead of returning the saturating
``entry_count`` header.
* ``UCXXClient`` preemptively closes pooled endpoints older
than ``_POOL_ENDPOINT_MAX_AGE_S`` on checkout, replacing
them with fresh connections so a client never tries to
reuse an endpoint the server has already idle-evicted.
* Demote the per-request ``[UCXXBuffer] req slot=...`` log
from INFO to DEBUG.
**Cleanup.** Removes the deprecated ``UCXXTrainerMixin``
(superseded by ``UCXXDataPackerMixin``) and the
``ucxx_n_chunks`` config knob. ``read_raw`` still tolerates
re-entry from ``READING`` -- not for chunking, but to let a
fresh handler serve a slot when the original is still
mid-``send``; the defensive guards above make the duplicate
finalise harmless.
**Docs.** ``ucxx/__init__.py`` and ``rl-gym/docs/UCXX.md``
rewritten with the slot-lifecycle diagram, the three-layer
retry table, port skip-list semantics, and the
preemptive-eviction self-healing window.
Tests: 55 unit tests in ``tests/test_ucxx_transport.py`` and
``tests/test_ucxx_data_packer_mixin.py`` covering the
defensive primitive guards, ``get_ready_count`` correctness,
stale-pooled-endpoint replacement, and the three-layer retry
behaviour.
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Summary
Reworks the UCXX payload transport for correctness and simplicity, and removes a deprecated trainer-side mixin.
send([slot])→recv(status)→recv(payload). The handler that does the slot'sREADY→READINGtransition uniquely owns itsREADING→{FREE|READY}finalisation — no refcounting, no shared cross-handler state.mark_consumed/release_readingno-op with a warning on unexpected states); (2) single owner per read attempt (exactly one ofmark_consumed/release_readinginfinally).UCXXClient.read); per-slot fresh-call retry with non-retryableStaleSlotError(_read_one); multi-round batch retry (_ucxx_dp_fetch_all).Test plan
tests/test_ucxx_transport.py(single-chunk protocol, slot-state invariants, port quarantine/rotation)tests/test_ucxx_data_packer_mixin.py