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Receive tasks

Receive tasks reference a message; these are used to wait until a proper message is received.

Receive Tasks

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

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

:::inote An alternative to receive tasks is a message intermediate catch event, which behaves the same way 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 process 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 number.

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 process instance has a variable orderId with value "order-123", the message is published with the correlation key "order-123".

Variable mappings

Output variable mappings are used to customize how variables are merged into the process instance. These can contain multiple elements that specify which variables should be mapped. The Process Variable Name of an output denotes the variable name outside the activity.

Visit our documentation on input and output variable mappings for more information on this topic.

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>

References