Tasks

Tasks are the atomic units of work in a Fleans workflow. Each task maps to a <bpmn:*Task> element and runs exactly once per activation. Fleans supports four task variants; a fifth (Send Task) is not yet implemented — see Send Task below.

See also: BPMN Support matrix for the full coverage table.

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Each task type reaches the WorkflowInstance its own way: plain tasks complete at once, scripts run in the evaluator, user tasks wait for a person, and service tasks run on a gRPC worker. Open interactive diagram ↗

Plain Task

A Plain Task (<bpmn:task>) completes immediately with no executor — the engine advances to the next element as soon as activation is recorded. Use it for modelling a human activity or a placeholder that will be replaced later.

BPMN:

<bpmn:task id="Task_1" name="Do something" />

Note

Plain Tasks auto-complete — they never block the workflow. Source: BpmnConverter.cs#L303.

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Script Task

A Script Task (<bpmn:scriptTask scriptFormat="csharp">) executes a C# expression via DynamicExpresso. The expression string is read from <camunda:script> and evaluated against a _context variable bag that exposes the current workflow variables.

BPMN:

<bpmn:scriptTask id="Task_1" name="Compute total" scriptFormat="csharp">
  <bpmn:extensionElements>
    <camunda:script><![CDATA[_context.total = _context.price * _context.qty]]></camunda:script>
  </bpmn:extensionElements>
</bpmn:scriptTask>

Note

_context is an ExpandoObject backed by the workflow’s variable store. Mutations are merged back after completion. Source: BpmnConverter.cs#L354.

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User Task

A User Task (<bpmn:userTask>) suspends the workflow and waits for a human to act. Fleans exposes a claim → complete (or fail / cancel) lifecycle via REST and the admin UI.

BPMN:

<!-- Requires xmlns:fleans="https://fleans.io/schema/bpmn/1.0" on <bpmn:definitions> -->
<bpmn:userTask id="Task_1" name="Approve request">
  <bpmn:extensionElements>
    <fleans:assignmentDefinition assignee="manager" candidateGroups="approvers" />
  </bpmn:extensionElements>
</bpmn:userTask>

Note

assignee and candidateGroups are stored as task metadata. The workflow is paused until the task is completed via POST /Execution/complete-activity. Source: BpmnConverter.cs#L313.

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Service Task (Custom Task)

A Service Task (<bpmn:serviceTask type="…">) delegates execution to a handler identified by the type attribute. It runs on a worker connected over gRPC — your own, or the ready-made plugins’ image; the engine images bundle none — and its result comes back through <fleans:output> bindings.

BPMN:

<!-- Requires xmlns:fleans="https://fleans.io/schema/bpmn/1.0" on <bpmn:definitions> -->
<bpmn:serviceTask id="Task_1" name="Call external API">
  <bpmn:extensionElements>
    <fleans:taskDefinition type="rest-call" />
    <fleans:ioMapping>
      <fleans:input source="=apiUrl"  target="url" />
      <fleans:output source="=__response.body" target="result" />
    </fleans:ioMapping>
  </bpmn:extensionElements>
</bpmn:serviceTask>

The type value must match the task type a worker registers — rest-call above is the REST Caller plugin from fleans-plugins. To learn more:

• Custom Tasks — architecture, event flow, parameter mapping, and the ready-made plugins.
• Input/Output Mapping — the <fleans:ioMapping> expression syntax, shared by every task type.
• Hosting workers — run workers next to the engine.
• Writing custom tasks — step-by-step authoring guide.

Camunda back-compat

Files exported from Camunda Zeebe (e.g. <extensionElements><zeebe:taskDefinition type="..."/></extensionElements>) are accepted as-is — the BPMN converter understands both <fleans:taskDefinition> and the legacy <zeebe:taskDefinition> shape. New Fleans-authored files should use the <fleans:...> namespace; see BPMN extension namespaces for the convention.

Source: BpmnConverter.cs#L333.

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Input/output mapping

Every task type accepts <fleans:ioMapping>: inputs compute task-local variables from C# expressions before the task runs, and outputs pick what it hands back to the process. See Input/Output Mapping.

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Send Task

Send Task (<bpmn:sendTask>) is not yet implemented in Fleans. If a BPMN file contains a Send Task, the converter will not recognise it and the element will be skipped or cause a parse error. A dedicated fixture and implementation are tracked in issue #420-E.