* Studio: serialize the compare-mode dispatcher lifecycle to fix a start race
_generate_dispatched (compare mode) bypasses _gen_lock so two concurrent
compare requests can both reach _start_dispatcher. The check-then-spawn there
had no lock, so both could observe no live dispatcher and each spawn one. The
extra dispatcher is orphaned (self._dispatcher_thread tracks only the last) and
during a later unload it can consume the 'unloaded' reply off _resp_queue before
unload_model's _wait_response, hanging the unload on its timeout.
Add _dispatcher_lifecycle_lock and take it around the whole body of both
_start_dispatcher and _stop_dispatcher, so start/stop cannot interleave and the
second concurrent starter sees the dispatcher alive and returns. _start_dispatcher
now returns whether it actually spawned the thread, and _generate_dispatched
derives dispatcher_preexisting from that atomic result instead of a separate
unlocked is_alive() read.
No call site holds _mailbox_lock when calling start/stop, so joining the
dispatcher (which takes _mailbox_lock) under the new lock cannot deadlock; the
lock order is always _gen_lock then _dispatcher_lifecycle_lock and is never
inverted.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
* Studio: refuse dispatcher start queued behind an unload's stop
A compare request could pass the early _unload_pending check, then block in _start_dispatcher on _dispatcher_lifecycle_lock behind an unload's _stop_dispatcher. When the unload released the lock the start spawned a fresh dispatcher, which became the resp_queue reader and consumed the worker's unroutable 'unloaded' reply before unload_model's _wait_response saw it, hanging the unload for 300s.
Gate _start_dispatcher on _unload_pending under the lifecycle lock, and set _unload_pending under the same lock ahead of the stop, so any start queued behind the stop observes the unload and refuses. Ordering stays _gen_lock -> _dispatcher_lifecycle_lock. Adds a regression test forcing the queued-behind-stop interleaving.
* [pre-commit.ci] auto fixes from pre-commit.com hooks
for more information, see https://pre-commit.ci
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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
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