# Background Workers (/Nyx/server/workers)



Background Workers [#background-workers]

To keep the primary API fast and responsive, tasks that do not need to block the HTTP/WebSocket response cycle are offloaded to background workers.

Types of Workers [#types-of-workers]

Nyx currently utilizes background processing for the following tasks:

1. **Presence Pruning**: A periodic job that sweeps the Redis `conversationConnections` sets. It removes stale connection references (e.g., if a server node crashed and didn't gracefully close its sockets) and recalculates the `conversationUsers` online counts to ensure absolute accuracy.
2. **Delivery Replays**: If a user connects to a room and has pending "Sent" messages that haven't been marked as "Delivered", a background routine fetches these from Postgres and re-emits them to the newly connected socket.

Implementation Details [#implementation-details]

Workers are initialized during the main `Bun` application boot process (usually inside `src/main.ts` or triggered via `setInterval` in the `realtime.ts` bridge).

Because Nyx runs in a distributed environment, care must be taken to ensure workers do not conflict:

* **Stateless Jobs**: Tasks like Presence Pruning are safe to run concurrently across nodes because Redis operations (like `SREM` and `HINCRBY`) are atomic.
* **Node-Specific Jobs**: Delivery replays are tied specifically to the node that currently holds the active WebSocket connection.

<Mermaid
  chart="`graph TD
  Cron[Timer] -->|Tick| Prune(Prune Presence Job)
  Prune -->|Fetch Stale Refs| Redis[(Redis)]
  Prune -->|Calculate True Online Count| Redis
  Redis -->|Emit userOffline| EventBus(Global Event Bus)`"
/>