Skip to main content

​
Queue And Redis

The driver uses Redis and BullMQ so print jobs survive process errors and printer outages.

​
Per-Printer Queues

Each unique ip_address:port gets a dedicated PrinterStore. For example: 
192.168.1.50:9100 -> pc-printer_192_168_1_50_9100
192.168.1.51:9100 -> pc-printer_192_168_1_51_9100
Each store owns:
  • One BullMQ queue.
  • One BullMQ worker.
  • One queue events listener.
  • One printer status cache.
  • One socket lifecycle controller.
Worker concurrency is 1, so one printer never receives two jobs at the same time. Different printers can process in parallel because each printer has its own worker.

​
Printer Registry

Known printers are stored in the Redis set: 
pc-printer:printers
On startup, restorePersistedStores() reads the set, recreates stores, and retries failed jobs.

​
Retry Behavior

Default queue options: 
{
  "attempts": 2147483647,
  "backoff": {
    "type": "fixed",
    "delay": 5000
  },
  "removeOnComplete": true,
  "removeOnFail": false
}
This means:
  • Completed jobs are removed.
  • Failed jobs are retained.
  • Failed jobs retry with fixed backoff.
  • The default maxAttempts effectively retries forever.

​
Scheduled Jobs

POST /print accepts runAt. If runAt is in the future, the driver adds the job with a BullMQ delay. If a delayed job was created for a future schedule, recovery logic does not promote it early. Accepted runAt forms:
  • Millisecond timestamp number.
  • Numeric string.
  • Date string that Date.parse() can parse.

​
Queue Status

GET /queue-status aggregates all known stores:
  • waiting
  • active
  • delayed
  • failed
  • completed
  • totalPending
  • isProcessing
totalPending is waiting + delayed across all stores.

​
Embedded Redis

Embedded mode starts Redis through redis-memory-server. On Windows, the driver checks or downloads the requested Redis binary: 
redis-binaries/<version>/Redis-<version>-Windows-x64-msys2/redis-server.exe
The actual running Redis version is checked after startup. If the detected version does not equal config.redis.version, startup aborts.

​
Disk Sync

When redis.diskSync is true, Redis starts with snapshot settings: 
--save <snapshotIntervalSec> 1
--appendonly no
--dir <app-root>
--dbfilename dump.rdb
On graceful shutdown, the driver attempts a Redis SAVE. Use disk sync when you need queues and known printers to survive restarts.

​
External Redis

External mode does not start or stop Redis. The driver uses: 
{
  "mode": "external",
  "host": "127.0.0.1",
  "port": 6379,
  "db": 0,
  "username": "",
  "password": ""
}
Use external Redis when a store already has managed Redis or when multiple driver processes need shared queue state. Avoid pointing two active drivers at the same physical printers unless the operational model is explicit.