Events

Execution Workflow

• Decide whether the event bus is the right tool: decoupled in-process side effects, not app lifecycle or broker-backed messaging.

• Define stable event IDs and argument contracts before wiring emitters and listeners.

• Register listeners on the Litestar app with listeners=[...] .

• Emit events from handlers or services through request.app.emit(...) or another app reference.

• Keep listeners independent so multiple listeners can react to the same event safely.

• Replace the default emitter backend only when retry, persistence, or external infrastructure requirements justify it.

Core Rules

• Treat event IDs as stable contracts, not ad hoc strings scattered through the codebase.

• Make every listener for an event compatible with the full emitted *args and **kwargs set.

• Use **kwargs defensively when multiple listeners consume different subsets of the same event payload.

• Keep listener bodies side-effect focused and small; delegate heavy domain logic to services.

• Use the built-in in-memory emitter for simple in-process async fanout.

• Implement a custom emitter backend only when persistence, retry, scheduling, or external transport is required.

• Do not confuse the event bus with on_startup / on_shutdown ; those are different Litestar mechanisms.

Decision Guide

• Use events when one action should trigger one or more async side effects without coupling the route handler to each implementation.

• Use multiple listeners when several side effects should react to the same event independently.

• Use one listener with multiple event IDs only when the argument contract and behavior are genuinely shared.

• Use a custom backend when event delivery must survive process boundaries or support retry/history semantics.

• Use litestar-channels instead when the problem is real pub-sub or cross-process fanout.

• Use litestar-app-setup instead when the task is startup/shutdown initialization.

Reference Files

Read only the sections you need:

• For listener registration, multi-event listeners, multiple listeners, argument-shape rules, emission patterns, and service-layer design, read references/listener-patterns.md.

• For backend selection, SimpleEventEmitter , custom backend requirements, async context manager behavior, and failure semantics, read references/emitter-backends.md.

Recommended Defaults

• Centralize event ID constants or naming rules.

• Emit keyword arguments instead of positional arguments when contracts may evolve.

• Keep listener signatures tolerant of extra kwargs when multiple listeners share an event.

• Prefer the default SimpleEventEmitter unless concrete requirements force a custom backend.

• Keep emitted payloads domain-oriented and free of request-specific transport details where possible.

Anti-Patterns

• Using events for startup/shutdown resource management.

• Emitting inconsistent argument shapes for the same event ID.

• Writing listeners that break as soon as another listener needs an extra kwarg.

• Hiding critical synchronous business steps behind fire-and-forget event listeners.

• Reaching for a custom backend before the in-process emitter's limits are real.

• Using events as a substitute for channels when cross-process delivery is required.

Validation Checklist

• Confirm each emitted event ID has an intentional contract and owner.

• Confirm every listener can accept the full emitted arg/kwarg shape.

• Confirm multiple listeners for the same event remain independent and idempotent enough for the use case.

• Confirm event emission is placed after the authoritative state change that should trigger it.

• Confirm the default emitter backend is sufficient, or document why a custom backend is required.

• Confirm listener failures do not accidentally cancel sibling listeners.

• Confirm tests cover both emission side effects and listener argument compatibility.

Cross-Skill Handoffs

• Use litestar-app-setup for startup/shutdown hooks and lifespan ownership.

• Use litestar-lifecycle-hooks for request/response interception and instrumentation.

• Use litestar-channels for broker-backed or cross-process publish-subscribe flows.

• Use litestar-testing for event-emission assertions and listener-failure tests.

Litestar References

• https://docs.litestar.dev/2/usage/events.html

• https://docs.litestar.dev/2/reference/events.html

• https://docs.litestar.dev/2/reference/config.html