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Contest Worker

The Contest Worker handles the periodic synchronization of external coding contests (from platforms like Codeforces, LeetCode, CodeChef, etc.) into the local platform database.

File Location: api/src/workers/contest/contest.worker.ts

Architecture

Unlike the other workers which react to user events (like submitting code), the Contest Worker operates on a cron-schedule.

  • Queue Engine: BullMQ contestSyncQueue.
  • Concurrency: Hardcoded to 1. This is absolutely critical to prevent concurrent workers from scraping third-party APIs simultaneously and triggering IP bans or rate limits.

Scheduling Strategy

  1. Repeatable Job: On startup, initContestSyncSchedule() creates a BullMQ repeatable job using the cron pattern 0 */6 * * * (Every 6 hours).
  2. Deduplication: It clears any existing repeatable jobs by key before adding the new one to prevent orphaned cron jobs from stacking up across deployments.
  3. Cold Start: It immediately fires a one-time "initial-sync" job so that fresh deployments populate the database instantly without having to wait 6 hours.

When the job fires, it delegates to contestService.syncExternalContests().