Engines overview

z4j supports six engines, each with its own adapter package (z4j-<engine>).

Engine	Package	Broker	Strengths	Default scheduler
Celery	z4j-celery	Redis / RabbitMQ / SQS	Massive ecosystem, chords/groups/chains	celery-beat
RQ	z4j-rq	Redis	Simple, small surface, Python-only	rq-scheduler
Dramatiq	z4j-dramatiq	Redis / RabbitMQ	Reliable, middleware-first	APScheduler
Huey	z4j-huey	Redis / Sqlite / in-memory	Minimal deps, great for Django	built-in periodic
arq	z4j-arq	Redis	Async-native, great for FastAPI	arq cron
taskiq	z4j-taskiq	Redis / RabbitMQ / NATS / in-memory	Modern async, pluggable brokers	taskiq-scheduler

Installing

Pick one or more. They can coexist in the same process:

pip install z4j-celery z4j-rq z4j-dramatiq

Capability matrix

Advertised action	Celery	RQ	Dramatiq	Huey	arq	taskiq
Submit task	✓	✓	✓	✓	✓	✓
Retry task	✓	✓	✓	✓	-	-
Cancel task	✓	✓	-	✓	✓	-
Bulk retry	✓	✓	-	-	-	-
Purge queue	✓	✓	✓	-	-	-
Requeue dead letter	-	✓	-	-	-	-
List dead letters	-	✓	-	-	-	-

The matrix shows each adapter's default capabilities. Dramatiq additionally promotes pending-only cancel when z4j-dramatiq[abort] is installed and the broker contains a real dramatiq_abort.Abortable middleware, and promotes dead-letter listing on its Redis, RabbitMQ and stub brokers. Huey's default cancel is also pending-only. Neither adapter interrupts running work. The dashboard and API gate retry and cancel controls on the capabilities advertised by the connected adapter; they do not synthesize unsupported retry, cancel, bulk, or purge actions. Celery additionally advertises its remote worker-control operations; see the engine page for that wider surface.

Event capture strategy

Each adapter uses the engine's native signal / middleware / hook system:

Engine	Capture mechanism
Celery	task_received / task_prerun / task_postrun / task_retry / task_failure / task_revoked signals, plus a broker-events consumer in the worker's main process for the events prefork children raise
RQ	wrap of Worker.execute_job (the parent-side execution boundary) + optional per-job callbacks
Dramatiq	custom Middleware that hooks after_enqueue / before_process_message / after_process_message
Huey	handlers on eleven Huey signals, from SIGNAL_ENQUEUED / SIGNAL_EXECUTING / SIGNAL_COMPLETE to the retry, error, revoke, lock and expiry signals
arq	on_job_start / on_job_end hooks on the worker
taskiq	middleware: TaskiqMiddleware.pre_send / pre_execute / post_execute / on_error

Patches are additive - they don't replace your existing signal handlers.

Per-engine pages

See the left sidebar - one page per engine with install, config, events, actions, and caveats.