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BPMN ElementsEventsSignals

Signals

Signals are broadcast to all instances waiting on a matching signal reference — unlike messages, which target a single instance.

<intermediateCatchEvent id="waitForShutdown">
  <signalEventDefinition signalRef="SystemShutdown" />
</intermediateCatchEvent>

Broadcasting a signal

curl -X POST http://localhost:3000/api/signals \
  -H "Content-Type: application/json" \
  -d '{
    "signalName": "system.shutdown",
    "variables": { "reason": "maintenance" }
  }'

All instances with an active subscription for system.shutdown are woken simultaneously. The response includes the count of woken instances and new instances created via signal start events.

Delivery tiers

Signal broadcast follows the same 4-tier dispatch as messages but without correlation key filtering:

  1. Signal boundary subscriptions — all instances with matching boundary events
  2. Intermediate signal catch subscriptions — all waiting catch events
  3. Signal start definitions — creates new instances for each matching start event
  4. Event subprocess subscriptions — triggers signal ESPs in all matching instances

No correlation

Signals have no correlation mechanism. Every instance waiting on the signal reference receives the broadcast. Use messages when you need to target a specific instance.

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MessagesBoundary Events