"""Download worker process entry point. Runs in a DEDICATED container (`command: python -m app.worker`, `WORKER_ENABLED=1`), separate from the API so long yt-dlp downloads + ffmpeg postprocessing never block web requests. Design: * N loop threads (download_worker_concurrency) each claim a `queued` DownloadJob with FOR UPDATE SKIP LOCKED and process it. * The shared MediaAsset is the dedup unit. A job whose asset is already `ready` finishes instantly (no re-download); a fresh asset is claimed pending→downloading by exactly one worker (a DB compare-and-set), so two jobs for the same video+format never double-download. * Live progress is written to the job row (short-lived sessions, throttled ~1/s) — the frontend polls it; the worker can't reach the API's in-process WebSocket registry. * Pause/cancel are cooperative: the progress hook re-reads the job status and aborts the yt-dlp download if it's no longer `running`. * Crash-safe: on startup, orphaned `running` jobs are requeued and `downloading` assets reset. """ import logging import os import shutil import signal import subprocess import sys import threading import time from datetime import datetime, timezone from sqlalchemy import text from app import sysconfig from app.config import settings from app.db import SessionLocal from app.downloads import edit as editmod from app.downloads import quota, service from app.downloads.jobdb import ( _edit_staging_dir, _requeue_if_running, _reset_asset_pending, _set_job, _staging_dir, ) from app.downloads.status import STOPPED_BY_ROUTE, JobStatus from app.models import DownloadJob, MediaAsset log = logging.getLogger("siftlode.worker") _stop = threading.Event() def _handle_signal(signum, frame): _stop.set() # --- claim + recovery ----------------------------------------------------------------------- def _wait_for_schema(timeout: float = 300.0) -> bool: """Block until the download tables exist before doing any DB work. Returns False if they never appeared (or we were asked to stop while waiting). The API applies migrations on its OWN startup, and the worker is a separate container that may boot first (they start in parallel). Without this, the worker would hit a missing `download_jobs` table and crash-loop until the API's migrations land. Poll patiently instead — and if the schema is still absent when the timeout runs out, say so and let the caller exit, because "continuing" only moved the same crash one call further down (into `_recover_orphans`), where it read as an unrelated failure.""" deadline = time.monotonic() + timeout while not _stop.is_set(): try: with SessionLocal() as db: db.execute(text("SELECT 1 FROM download_jobs LIMIT 1")) return True except Exception as exc: # noqa: BLE001 — table not migrated yet / DB not up yet if time.monotonic() > deadline: log.error( "download schema still absent after %ss — the API's migrations have not landed; " "exiting so the container restarts: %s", timeout, str(exc)[:120], ) return False log.info("waiting for the database schema (API migrations)…") _stop.wait(3.0) return False def _recover_orphans() -> None: """Reset state left behind by a previous crash so nothing is stuck.""" with SessionLocal() as db: db.execute(text("UPDATE download_jobs SET status='queued' WHERE status='running'")) db.execute(text("UPDATE media_assets SET status='pending' WHERE status='downloading'")) db.commit() def _claim_job() -> int | None: """Claim the oldest queued job whose user is under their per-user concurrency limit AND whose shared asset isn't already being downloaded by another worker. The asset exclusion (`NOT EXISTS … media_assets.status='downloading'`) stops the same-asset ping- pong (B-sub-3): without it, a second worker claims a queued job that shares an in-flight asset, finds it busy, requeues it, and immediately re-claims it — burning a worker slot behind one in-flight asset and starving everyone else. Excluded here, that job simply waits until its asset settles, so `_process_job` no longer needs to sleep on the busy/lost-race paths. Users already AT their concurrency limit are excluded IN THE SQL, so one user flooding the queue can't monopolize the fetch window and starve everyone behind them. (The old fixed LIMIT-50 window did exactly that: 50 queued jobs from a single capped user filled the window, `chosen` came back None, and every other user's work — sitting past position 50 — was never seen.) The per-user limit is the quota row's `max_concurrent` (else the sysconfig default); `unlimited` users are never capped. A final Python `at_concurrency_limit` re-check still guards the tiny race between the exclusion subquery and the claim (it can only ever reject, never over-claim), so correctness never depends on the two observations agreeing.""" with SessionLocal() as db: default_mc = sysconfig.get_int(db, "download_default_max_concurrent") rows = db.execute( text( """ SELECT id, user_id FROM download_jobs WHERE status='queued' AND NOT EXISTS ( SELECT 1 FROM media_assets a WHERE a.id = download_jobs.asset_id AND a.status = 'downloading' ) AND user_id NOT IN ( SELECT r.user_id FROM download_jobs r LEFT JOIN download_quotas q ON q.user_id = r.user_id WHERE r.status='running' AND r.user_id IS NOT NULL GROUP BY r.user_id, q.max_concurrent, q.unlimited HAVING COALESCE(q.unlimited, false) = false AND count(*) >= GREATEST(COALESCE(q.max_concurrent, :dmc), 1) ) ORDER BY queue_pos, id FOR UPDATE SKIP LOCKED LIMIT 50 """ ), {"dmc": default_mc}, ).fetchall() chosen = next( (jid for jid, uid in rows if not quota.at_concurrency_limit(db, uid)), None ) if chosen is None: db.commit() # release the row locks; nothing eligible right now return None db.execute( text( "UPDATE download_jobs SET status='running', phase='starting', updated_at=now() " "WHERE id = :id" ), {"id": chosen}, ) db.commit() return chosen def _claim_asset(asset_id: int) -> bool: """Compare-and-set pending→downloading. True if THIS worker won the right to download.""" with SessionLocal() as db: row = db.execute( text( "UPDATE media_assets SET status='downloading' " "WHERE id = :id AND status='pending' RETURNING id" ), {"id": asset_id}, ).fetchone() db.commit() return row is not None # --- supervised child execution + watchdog -------------------------------------------------- # The heavy work runs in a child process so a wedged yt-dlp/ffmpeg is HARD-killable. A worker thread # can't be killed, a C-level spin (e.g. a catastrophic regex) can't even be cooperatively cancelled, # and one such thread starves the rest via the GIL — the incident that motivated this. The parent # thread supervises: it kills the child (and its process group, so ffmpeg grandchildren die too) on # a route pause/cancel, on a no-progress stall, or past an absolute wall-clock cap. # # POSIX-only: the kill path uses process groups (start_new_session / os.killpg / os.getpgid), so the # worker is Linux-container-only — never run `python -m app.worker` natively on Windows. # Edits ALSO carry a second, tighter watchdog inside run_ffmpeg (a per-ffmpeg stall timeout with a # cleaner "ffmpeg stalled" error); this process-level supervisor is the uniform backstop for both the # download and edit paths, and the last line of defence for anything run_ffmpeg can't see. _CHILD_OK = 0 def _spawn_download_child(job_id: int) -> subprocess.Popen: """Start the child that does the actual download/edit for `job_id`, in its OWN session/process group so stopping it also stops any ffmpeg / helper processes yt-dlp spawned.""" return subprocess.Popen( [sys.executable, "-m", "app.downloads.runner", str(job_id)], start_new_session=True, ) def _job_liveness(job_id: int) -> tuple[str | None, float | None]: """(status, seconds-since-last-row-update) for the job, computed with the DB clock so there is no parent↔DB skew. A live download rewrites its row ~1/s; a stalled one never does. Returns (None, None) if the row is gone.""" with SessionLocal() as db: row = db.execute( text( "SELECT status, EXTRACT(EPOCH FROM (now() - updated_at)) " "FROM download_jobs WHERE id = :id" ), {"id": job_id}, ).one_or_none() if row is None: return None, None return row[0], (float(row[1]) if row[1] is not None else None) def _signal_group(proc: subprocess.Popen, pgid: int | None, sig: int) -> None: """Signal the child's whole process group (falling back to the child alone), swallowing the race where it has already exited.""" try: if pgid is not None: os.killpg(pgid, sig) else: proc.send_signal(sig) except (ProcessLookupError, OSError): pass def _stop_child(proc: subprocess.Popen, grace_s: float) -> None: """SIGTERM the child's process GROUP, then SIGKILL if it outlives the grace period. Shares the terminate→wait→kill escalation with run_ffmpeg (`editmod.escalate_kill`); the only difference is that we signal the whole group so ffmpeg grandchildren die too. `escalate_kill` no-ops if the child already exited, and `getpgid` yields None for a reaped pid, so no separate poll guard.""" try: pgid: int | None = os.getpgid(proc.pid) except OSError: pgid = None editmod.escalate_kill( proc, terminate=lambda: _signal_group(proc, pgid, signal.SIGTERM), kill=lambda: _signal_group(proc, pgid, signal.SIGKILL), grace_s=grace_s, label="download child", ) def _stop_and_free(job_id: int, asset_id: int, proc: subprocess.Popen, grace_s: float) -> None: """Kill the child, free its claimed asset, and clear its staging — the common tail of every path that stops a child (a route pause/cancel, a shutdown, an over-cap abandon).""" _stop_child(proc, grace_s) _reset_asset_pending(asset_id) _cleanup_staging(asset_id) def _fail_after_kill( job_id: int, asset_id: int, proc: subprocess.Popen, grace_s: float, error: str, error_code: str ) -> None: """`_stop_and_free` + mark the job errored — for the watchdog's stall/timeout kills and the supervisor-error fallback.""" _stop_and_free(job_id, asset_id, proc, grace_s) _set_job(job_id, status="error", error=error, error_code=error_code, phase=None) def _run_supervised(job_id: int, asset_id: int) -> None: """Run the heavy download/edit for an already-claimed asset in a child process and watchdog it. A clean child exit means the child already wrote the terminal job/asset state (done/error, or a cooperative pause via the in-child progress hook) — we leave it. We step in only when the child can't finish or self-abort: a route paused/cancelled it (kill, free the asset, keep the route's status), it made no progress for `stall_timeout` or ran past `wall_clock_max` (kill, fail the job), the worker is shutting down (kill, requeue), or it crashed without setting state.""" poll_s = max(1, settings.download_supervisor_poll_seconds) stall_s = settings.download_stall_timeout_seconds wall_s = settings.download_wall_clock_max_seconds grace_s = settings.download_kill_grace_seconds try: proc = _spawn_download_child(job_id) except Exception: # noqa: BLE001 — spawn failed; don't leave the asset stuck 'downloading' log.exception("failed to spawn download child for job %s", job_id) _reset_asset_pending(asset_id) _requeue_if_running(job_id, None) return started = time.monotonic() reason: str | None = None try: while True: try: proc.wait(timeout=poll_s) break # child finished on its own except subprocess.TimeoutExpired: pass status, stale = _job_liveness(job_id) if status is None or status in STOPPED_BY_ROUTE: reason = "cancelled" # a route stopped it (or the row vanished) break if status == "running": if stale is not None and stale > stall_s: reason = "stalled" break if _stop.is_set(): reason = "shutdown" break # Absolute wall-clock cap frees the worker slot even for a FINISHED child wedged in # teardown. A still-running job over the cap is failed ("timeout"); a terminal one (already # done/error) just gets its lingering child killed, its DB status left intact ("abandon"). if time.monotonic() - started > wall_s: reason = "timeout" if status == "running" else "abandon" break # else: a terminal status under the cap (done/error, or a re-queued contended asset) means # the child is exiting on its own — keep polling; NEVER kill a finishing child (that could # drop its completion notice). except Exception: # noqa: BLE001 — a watchdog error must NEVER leave the child running unsupervised log.exception("supervisor loop failed for job %s; stopping the child", job_id) _fail_after_kill( job_id, asset_id, proc, grace_s, "The download was stopped after a worker error.", "unknown" ) return if reason is None: # Child exited. Reconcile the asset we claimed: free it if the child left it non-finalized — # a crash/OOM, or an early return on a job deleted mid-flight — a no-op when it finalized # normally. Then, if it died non-zero while the job is still 'running', fail the job so it is # not left stuck. Guarded: the child is already dead, so a DB blip here must not propagate. try: _reset_asset_pending(asset_id) if proc.returncode != _CHILD_OK: status, _ = _job_liveness(job_id) if status == "running": _cleanup_staging(asset_id) _set_job( job_id, status="error", error_code="unknown", phase=None, error=f"The download process exited unexpectedly (code {proc.returncode}).", ) log.warning("job %s: child exited %s without finishing", job_id, proc.returncode) except Exception: # noqa: BLE001 — boot recovery is the backstop for a stuck 'running' job log.exception("post-exit reconciliation failed for job %s", job_id) return if reason == "stalled": _fail_after_kill( job_id, asset_id, proc, grace_s, f"The download stalled (no progress for {int(stall_s)}s) and was stopped.", "network", ) return if reason == "timeout": _fail_after_kill( job_id, asset_id, proc, grace_s, f"The download exceeded the {int(wall_s)}s time limit and was stopped.", "network", ) return # cancelled / abandon / shutdown: stop + free the asset, but leave the job's own DB status. _stop_and_free(job_id, asset_id, proc, grace_s) if reason == "shutdown": _requeue_if_running(job_id, None) # resume on the next boot elif reason == "abandon": log.warning("job %s: killed a child wedged past the wall-clock; DB status left intact", job_id) else: # cancelled log.info("job %s: child stopped (route pause/cancel)", job_id) def _cleanup_staging(asset_id: int) -> None: """Best-effort removal of a killed child's leftover staging dirs (its own `finally` never ran). The next attempt on this asset also wipes staging on start, so this is just tidiness/disk.""" for path in (_staging_dir(asset_id), _edit_staging_dir(asset_id)): shutil.rmtree(path, ignore_errors=True) # --- processing ----------------------------------------------------------------------------- def _process_job(job_id: int) -> None: """Dispatch a claimed job. The trivial outcomes (cache hit, dead/contended asset) are handled inline and cheaply; the actual heavy work (yt-dlp download / ffmpeg edit) is claimed here and then run in a supervised CHILD PROCESS (`_run_supervised`) so a wedged yt-dlp/ffmpeg can be hard-killed — a worker THREAD cannot be killed, nor (when it spins in a C call) even cooperatively cancelled, and one such thread starves the others via the GIL.""" with SessionLocal() as db: job = db.get(DownloadJob, job_id) if job is None: return asset = db.get(MediaAsset, job.asset_id) if job.asset_id else None asset_id = asset.id if asset else None asset_status = asset.status if asset else None asset_error = asset.error if asset else None if asset is None: _set_job(job_id, status="error", error="No media asset", phase=None) return if asset_status == "ready": _finish_from_cache(job_id, asset_id) return if asset_status == "error": _set_job(job_id, status="error", error=asset_error or "Download failed", phase=None) return if asset_status == "downloading": # Another worker won this asset between our claim and here (a narrow race — the claim SQL # excludes downloading-asset jobs). Requeue and let it be reclaimed once the asset settles; # no sleep — the claim exclusion keeps it out of the window until then, so no busy-loop. _requeue_if_running(job_id, "waiting") return # asset_status == "pending": try to win the download / edit. if not _claim_asset(asset_id): # Lost the pending->downloading race; requeue (same reasoning — the exclusion prevents a spin). _requeue_if_running(job_id, "waiting") return # The asset is now ours ('downloading'): run the heavy work in a supervised child process. _run_supervised(job_id, asset_id) def _finish_from_cache(job_id: int, asset_id: int) -> None: with SessionLocal() as db: job = db.get(DownloadJob, job_id) asset = db.get(MediaAsset, asset_id) if job and asset: fields = {"status": JobStatus.DONE, "progress": 100, "phase": None} if not job.display_name and asset.title: # display_name is VARCHAR(255); a title can be longer (e.g. a recipe in the title). fields["display_name"] = asset.title[:255] asset.last_access_at = datetime.now(timezone.utc) # Atomic finalize: only marks the job done while it is still running, so a concurrent # cancel/pause is never resurrected (see service.finalize_if_running). service.finalize_if_running(db, job_id, **fields) db.commit() # --- loop ----------------------------------------------------------------------------------- def _worker_loop(idx: int) -> None: while not _stop.is_set(): try: job_id = _claim_job() except Exception: # noqa: BLE001 log.exception("claim failed") _stop.wait(settings.download_poll_seconds) continue if job_id is None: _stop.wait(settings.download_poll_seconds) continue try: _process_job(job_id) except Exception: # noqa: BLE001 log.exception("processing job %s crashed", job_id) _set_job(job_id, status="error", error="Worker error", phase=None) def main() -> None: logging.basicConfig(level=logging.INFO) signal.signal(signal.SIGTERM, _handle_signal) signal.signal(signal.SIGINT, _handle_signal) if not settings.worker_enabled: log.info("WORKER_ENABLED is off; worker exiting (nothing to do).") return # The API may still be applying migrations when we boot. If they never arrive, exit instead of # pressing on into a guaranteed crash — with a FAILURE status, so the container comes back under # any restart policy (`on-failure` too, not just the `unless-stopped` our composes ship) and the # exit code doesn't claim success for a worker that never started working. if not _wait_for_schema(): if _stop.is_set(): return # asked to shut down while waiting — that IS a clean exit raise SystemExit(1) _recover_orphans() n = max(1, settings.download_worker_concurrency) log.info("Download worker started (concurrency=%d, root=%s).", n, settings.download_root) threads = [threading.Thread(target=_worker_loop, args=(i,), daemon=True) for i in range(n)] for t in threads: t.start() while not _stop.is_set(): _stop.wait(1.0) log.info("Download worker stopping…") for t in threads: t.join(timeout=5) if __name__ == "__main__": main()