Receive Tasks

Receive tasks are tasks which references a message. They are used to wait until a proper message is received.

Receive Tasks

When a receive task is entered then a corresponding message subscription is created. The workflow instance stops at this point and waits until the message is correlated.

A message can published using one of the Zeebe clients. When the message is correlated, the receive task gets completed and the workflow instance continues.

An alternative to receive tasks are message intermediate catch events which behaves the same but can be used together with event-based gateways.

Messages

A message can be referenced by one or more receive tasks. It must define the name of the message (e.g. Money collected) and the correlationKey expression (e.g. = orderId).

Usually, the name of the message is defined as a static value (e.g. order canceled), but it can also be defined as expression (e.g. = "order " + awaitingAction). The expression is evaluated on activating the receive task and must result in a string.

The correlationKey is an expression that usually accesses a variable of the workflow instance that holds the correlation key of the message. The expression is evaluated on activating the receive task and must result either in a string or in a number.

In order to correlate a message to the receive task, the message is published with the defined name (e.g. Money collected) and the value of the correlationKey expression. For example, if the workflow instance has a variable orderId with value "order-123" then the message must be published with the correlation key "order-123".

Variable Mappings

By default, all message variables are merged into the workflow instance. This behavior can be customized by defining an output mapping at the receive task.

Additional Resources

XML representation

A receive task with message definition:

<bpmn:message id="Message_1iz5qtq" name="Money collected">
   <bpmn:extensionElements>
     <zeebe:subscription correlationKey="orderId" />
   </bpmn:extensionElements>
</bpmn:message>

<bpmn:receiveTask id="money-collected" name="Money collected"
  messageRef="Message_1iz5qtq">
</bpmn:receiveTask>

Using the BPMN modeler

Adding a receive task with message:

receive-task

Workflow Lifecycle

Workflow instance records of a receive task:

Intent Element Id Element Type
ELEMENT_ACTIVATING money-collected RECEIVE_TASK
ELEMENT_ACTIVATED money-collected RECEIVE_TASK
... ... ...
EVENT_OCCURRED money-collected RECEIVE_TASK
ELEMENT_COMPLETING money-collected RECEIVE_TASK
ELEMENT_COMPLETED money-collected RECEIVE_TASK

References: