- extractor._try_acquire_file_lock: close fd and re-raise on non-
BlockingIOError from fcntl.flock (read-only fs, unsupported flock,
fd exhaustion). Pre-fix the fd leaked silently and the underlying
OSError still propagated past the caller.
- extractor: reorder module-level layout so logger is bound before
the new lock-related helpers reference it. Deferred import of
app.instance_config inside _get_lock_ttl_seconds documented inline.
- extractor: comment _table_locks unbounded-by-design rationale.
- tests: docstring + monkeypatch-target rationale for the two
concurrency tests where the contract isn't obvious from the body.
Two layers of concurrency control. Layer 1 is a per-table_id
threading.Lock keyed on table_id; Layer 2 is fcntl.flock on a sibling
<id>.parquet.lock file. Overlapping calls for the same id raise
MaterializeInFlightError, which the caller treats as 'skipped,
in_flight' instead of a hard error. Stale file locks (mtime older
than materialize.lock_ttl_seconds, default 86400) are reclaimed on
the next attempt — covers the rare case where a holder was hard-killed
before kernel-level flock release.
Pre-fix, when a materialize ran longer than the scheduler tick interval
(15 min), the next tick called materialize_query for the same id, hit
the unconditional tmp_path.unlink() at function entry, and started a
second COPY against the same path. Both writers interleaved bytes;
the original COPY's read_parquet validation then failed with
'No magic bytes found at end of file'.
