Discord-reported (fresh.dumbledore + maintainer ack): the
/api/import/singles/process route iterated staging files through a
plain Python for loop. Per-file work is dominated by metadata
search round-trips (Spotify/iTunes/Deezer/Discogs), so a multi-
track manual import on a typical home network was painfully slow.
Adds a dedicated import_singles_executor (3 workers) alongside the
existing executor pool, and refactors the route to submit every
file at once and aggregate results via as_completed. Worker count
balances throughput against any single provider's per-source rate
limits — the same shape used by missing_download_executor.
Extracts the per-file pipeline into _process_single_import_file
which returns a typed (status, payload) outcome:
- ("ok", final_title) on success
- ("error", message) for missing/malformed input or pipeline failure
The worker wraps its own exceptions so a single bad file can't
crash the batch; the route adds a belt-and-suspenders try/except
around future.result() for any worker-level surprises.
Pipeline thread-safety verified: post_process_matched_download
already serializes per-file via post_process_locks (one lock per
context_key — and each import gets a unique UUID context_key), DB
writes serialize through SQLite's WAL + busy_timeout, metadata
registry uses RLocks, no bare module-level mutable state.
Adds 9 regression tests:
- 4 worker-contract tests (missing file, malformed match, pipeline
exception wrapping, happy-path return shape)
- 2 executor-config tests (worker count, thread name prefix)
- 1 integration test that proves the route actually parallelizes
by checking wall-clock duration is well under sequential cost
- 1 mixed-outcome aggregation test
- 1 worker-crash recovery test
Doesn't address the related "stops on tab close" complaint —
that's a separate request-lifecycle issue that needs job_id +
polling, not just parallelism.
Broque Thomas