Process Gets stuck when parallel branch has no parallel join

[mhanrahan]

We recently updated our Activiti version from 5.16.3 to 5.21, and we have found a scenario in one of our existing processes where a process will get stuck with no way to recover the process.

Basically if you have a parallel gateway, one of the branches has a service task that is asynchronous, and the other branch is not asynchronous and flows through to an end event straight away, the branch that is asynchronous will never have a job fired to process the async continuation and be stuck forever.

This is a sample process that illustrates the issue:

<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:activiti="http://activiti.org/bpmn" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlnsmgdc="http://www.omg.org/spec/DD/20100524/DC" xmlnsmgdi="http://www.omg.org/spec/DD/20100524/DI" typeLanguage="http://www.w3.org/2001/XMLSchema" expressionLanguage="http://www.w3.org/1999/XPath" targetNamespace="http://www.activiti.org/test">
  <process id="ParallelGatewayTest" name="My ParallelGatewayTest" isExecutable="true">
    <startEvent id="startevent1" name="Start"></startEvent>
    <serviceTask id="servicetask1" name="Asynchronous Task" activiti:async="true" activiti:class="com.example.SomeListener"></serviceTask>
    <parallelGateway id="parallelgateway1" name="Parallel Gateway"></parallelGateway>
    <sequenceFlow id="flow1" sourceRef="startevent1" targetRef="parallelgateway1"></sequenceFlow>
    <sequenceFlow id="flow2" sourceRef="parallelgateway1" targetRef="servicetask1"></sequenceFlow>
    <serviceTask id="shouldAlwaysRun" name="Is Never Run" activiti:class="com.example.SomeOtherListener"></serviceTask>
    <sequenceFlow id="flow3" sourceRef="servicetask1" targetRef="shouldAlwaysRun"></sequenceFlow>
    <endEvent id="endevent1" name="End"></endEvent>
    <sequenceFlow id="flow4" sourceRef="shouldAlwaysRun" targetRef="endevent1"></sequenceFlow>
    <sequenceFlow id="flow5" sourceRef="parallelgateway1" targetRef="servicetask2"></sequenceFlow>
    <serviceTask id="servicetask2" name="Flow Through task" activiti:class="com.example.SomeThirdListener"></serviceTask>
    <sequenceFlow id="flow6" sourceRef="servicetask2" targetRef="endevent1"></sequenceFlow>
  </process>
</definitions>

Adding a parallel join at the end resolves the issue, but the process I am working with is much more complicated than this example.

Any other suggestions?

[gdharley]

This is a known architectural issue and one of the main reasons for the engine redesign that is part of version 6.

You can read about the problem here:

Activiti 6: An Evolution of the Core Engine | Small steps with big feet 

Until you start using the Version 6 engine, you are best served using parallel joins after a parallel branch and I tend to use inclusive joins and branches as they tend to behave more predictably.

Cheers,

Greg

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