Static member is set to null by the process engine

[sor1]

Hello,
I have a static member:

public final class MySingletonClass
{
    public static MyClass MyUniqueObject;
}‍‍‍‍

MyClass is a class extending the interface Com4jObject.

I need to use this static object in 2 service tasks of my workflow: the first service task create it and start to use it. The second service task also use it (and dispose it).
I cannot set this object as a process variable as it is not serializable (com object).
My problem is that my static object is randomly set to null before I try to access it in the second service task.

Why is this static member set to null and how would you do solve this problem?

Thanks.

[jbarrez]

Can you post the process xml, cause I don't quite follow what you are trying to do.
Also, can you included the code of your service tasks?

[sor1]

public class MyFirstServiceTaskDelegate extends JavaDelegate
{
    public void execute(DelegateExecution execution)
    {
        MyClass connection = new MyClass();
        connection.login("MyUserName");
        MySingletonClass.MyUniqueObject = connection;                                           
    }
}public class MySecondServiceTaskDelegate extends JavaDelegate
{
    public void execute(DelegateExecution execution)
    {
        MySingletonClass.MyUniqueObject.logOff; // I have a java.lang.NullPointerException because MySingletonClass.MyUniqueObject is null!!
        MySingletonClass.MyUniqueObject.Dispose();
    }
}The process:
<process id="sid-ecb59ae4-724e-4e3a-913d-4ba70efe620a" name="MyProcess" isExecutable="true">

        <startEvent id="StartEvent" name="Start">
            <documentation id="sid-c4a36fd8-83f9-49ad-ae93-e090c82e6cbd">Comment…
            </documentation>
            <extensionElements>
                <signavio:signavioMetaData metaKey="bgcolor" metaValue="#ffffff"/>
            </extensionElements>
            <outgoing>sid-43298455-F11D-464C-A804-9999D7A63A52</outgoing>
        </startEvent>
        <serviceTask activiti:class="com.persistent.greenlab.workflow.scheduler.ValidCommandComingDelegate" completionQuantity="1" id="ValidAnalysis" implementation="webService" isForCompensation="false" name="Valid analysis is coming" startQuantity="1">
            <extensionElements>
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                <signavio:signavioMetaData metaKey="risklevel" metaValue=""/>
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            </extensionElements>
            <incoming>sid-43298455-F11D-464C-A804-9999D7A63A52</incoming>
            <outgoing>sid-16330616-A681-4C50-A56E-0D7824FF9C55</outgoing>
        </serviceTask>
        <exclusiveGateway gatewayDirection="Diverging" id="IsValidCommand" name="Valid Command?">
            <extensionElements>
                <signavio:signavioMetaData metaKey="bgcolor" metaValue="#ffffff"/>
            </extensionElements>
            <incoming>sid-16330616-A681-4C50-A56E-0D7824FF9C55</incoming>
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            <outgoing>sid-1A88D597-C65D-493F-BDE4-35B36CA3BB34</outgoing>
        </exclusiveGateway>
        <serviceTask activiti:class="com.persistent.greenlab.workflow.scheduler.InstrumentsCheckupDelegate" completionQuantity="1" id="InstrumentsCheckup" implementation="webService" isForCompensation="false" name="Instrument Checkup" startQuantity="1">
            <extensionElements>
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                <signavio:signavioMetaData metaKey="risklevel" metaValue=""/>
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            <outgoing>sid-E5F8C44A-9D50-4054-A75A-03675C2A77BB</outgoing>
        </serviceTask>
        <receiveTask completionQuantity="1" id="MonitoringInstrumentStatusChange" implementation="webService" instantiate="false" isForCompensation="false" name="Monitoring Instrument status change (until priority = 1)" startQuantity="1">
            <extensionElements>
                <signavio:signavioMetaData metaKey="bgcolor" metaValue="#ffffcc"/>
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        </receiveTask>
        <serviceTask activiti:class="com.persistent.greenlab.workflow.scheduler.UpdateAnalysisStateToScheduledDelegate" completionQuantity="1" id="UpdateAnalysisStateToScheduled" implementation="webService" isForCompensation="false" name="Update analysis state to scheduled" startQuantity="1">
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        </serviceTask>
        <exclusiveGateway gatewayDirection="Diverging" id="IsInstrumentInError" name="Instrument&#10;in error in Lab ?">
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                <signavio:signavioMetaData metaKey="bgcolor" metaValue="#ffffff"/>
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            <outgoing>sid-7AF88DEA-00C9-40F8-9725-5DB1925388A1</outgoing>
        </exclusiveGateway>
        <exclusiveGateway gatewayDirection="Diverging" id="IsInstrumentIdlePriorityOrder1" name="Instrument Idle&#10;and&#10;Priority order =1">
            <extensionElements>
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        </exclusiveGateway>
        <serviceTask activiti:class="com.persistent.greenlab.workflow.scheduler.MyFirstServiceTaskDelegate" completionQuantity="1" id="StartAnalysis" implementation="webService" isForCompensation="false" name="MyFirstServiceTask" startQuantity="1">
            <extensionElements>
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        </serviceTask>
        <parallelGateway gatewayDirection="Diverging" id="sid-CDB70F30-11B7-4936-917A-60C48CBB17D7" name="">
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        <serviceTask activiti:class="com.persistent.greenlab.workflow.scheduler.UpdateAnalysisStateToInProgressDelegate" completionQuantity="1" id="UpdateAnalysisStateToInProgress" implementation="webService" isForCompensation="false" name="Update analysis state to in progress" startQuantity="1">
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        <parallelGateway gatewayDirection="Converging" id="sid-3B14D52E-5449-44B9-B344-68EB68793C39" name="">
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        </parallelGateway>
        <serviceTask activiti:class="com.persistent.greenlab.workflow.scheduler.UpdateInstrumentStatusToRunningDelegate" completionQuantity="1" id="UpdateInstrumentStatusIdlToRunning" implementation="webService" isForCompensation="false" name="Update intrument status from idle to running" startQuantity="1">
            <extensionElements>
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        </serviceTask>
        <serviceTask activiti:async="true" activiti:class="com.persistent.greenlab.workflow.scheduler.MonitoringAnalysisDelegate" completionQuantity="1" id="MonitoringAnalysis" implementation="webService" isForCompensation="false" name="Monitoring Analysis" startQuantity="1">
            <extensionElements>
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        </serviceTask>
        <intermediateCatchEvent id="TimerWaitingEndOfRun" name="Waiting end of run">
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            <timerEventDefinition id="sid-6bc87052-3b45-4914-88b1-714fcfa104da">
                <timeDuration id="sid-2953e909-fb2e-4732-a092-a8b7715c1eba" xsi:type="tFormalExpression">${RunTime}</timeDuration>
            </timerEventDefinition>
        </intermediateCatchEvent>
        <exclusiveGateway gatewayDirection="Diverging" id="GateWayRunFinished" name="Run is finished?">
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        </parallelGateway>
        <serviceTask activiti:class="com.persistent.greenlab.workflow.scheduler.SendAnEmailDelegate" completionQuantity="1" id="sid-67D25F92-398D-4020-A0CD-BA527395F9B5" implementation="webService" isForCompensation="false" name="Send an e-mail" startQuantity="1">
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            <documentation id="sid-11623193-a6f4-4e85-a6b2-a9ce2c49e40c">Primary defined instrument is in error. Instrument used for analysis is: ${ChosenInstrumentName}. Please validate vial position on ${ChosenInstrumentName}.</documentation>
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                <activiti:formProperty id="VialNumber" name="Vial Number" readable="true" required="false" type="string" variable="VialNumber" writable="true"/>
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        <sequenceFlow id="sid-3294B7FF-FCB0-4A3B-8F06-9273A3C8F921" isImmediate="true" name="" sourceRef="sid-270AAB82-043E-4B33-96F3-E8B09651C221" targetRef="EndEvent"/>
        <sequenceFlow id="sid-43EA876B-AE52-409A-B142-0349ABC27640" isImmediate="true" name="" sourceRef="sid-67D25F92-398D-4020-A0CD-BA527395F9B5" targetRef="sid-2A87A051-E234-42DC-B153-6FFE5739D8AE"/>
        <sequenceFlow id="sid-D7362764-2A68-4E45-843E-0450D6008B3D" isImmediate="true" name="" sourceRef="UpdateAnalysisStateInProgressToEnded" targetRef="sid-270AAB82-043E-4B33-96F3-E8B09651C221"/>
        <sequenceFlow id="sid-D1E44199-7EB7-4A49-B104-6D6A9355838C" isImmediate="true" name="" sourceRef="StartAnalysis" targetRef="sid-CDB70F30-11B7-4936-917A-60C48CBB17D7"/>
        <sequenceFlow id="sid-0D2E4763-AFE9-46E2-BB78-9CEBB9914F7E" isImmediate="true" name="No" sourceRef="IsInstrumentInError" targetRef="UpdateAnalysisStateToScheduled">
            <conditionExpression id="sid-0dca0b5d-2c34-4199-93ed-da4ccb4c2ef2" xsi:type="tFormalExpression"> ${IsInstrumentInError==false}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-9A40CAAD-EA28-43D3-B0B6-89129321B64B" isImmediate="true" name="" sourceRef="sid-CDB70F30-11B7-4936-917A-60C48CBB17D7" targetRef="UpdateAnalysisStateToInProgress"/>
        <sequenceFlow id="sid-615FBB43-F773-4701-9C35-5860E7AE10B2" isImmediate="true" name="No" sourceRef="DoesUserContinue" targetRef="UpdateAnalysisStateToError">
            <conditionExpression id="sid-cb9cfe8e-f4b5-4a51-bc3e-015a064413e0" xsi:type="tFormalExpression"> ${empty VialNumber}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-43298455-F11D-464C-A804-9999D7A63A52" isImmediate="true" name="" sourceRef="StartEvent" targetRef="ValidAnalysis"/>
        <sequenceFlow id="sid-41894BD6-0CAB-47DB-992F-1882A517AB9F" isImmediate="true" name="" sourceRef="UpdateAnalysisStateToError" targetRef="EndEventError"/>
        <sequenceFlow id="sid-C917E421-F0E4-4F6D-A644-1A750404D45E" isImmediate="true" name="Yes" sourceRef="IsInstrumentIdlePriorityOrder1" targetRef="StartAnalysisInEZChrom">
            <conditionExpression id="sid-cd925f7c-e81d-42be-983d-040a029e8dad" xsi:type="tFormalExpression"> ${IsInstrumentIdle==true}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-408E46D7-84BE-4D3E-A767-68F89091C695" isImmediate="true" name="No" sourceRef="IsInstrumentIdlePriorityOrder1" targetRef="IsInstrumentInError">
            <conditionExpression id="sid-f287908b-bf26-4b03-a876-f91bd4134013" xsi:type="tFormalExpression"> ${IsInstrumentIdle==false}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-37FCF0E5-45E5-468B-A37F-9B9379C41B58" isImmediate="true" name="" sourceRef="sid-6C7071D6-CE99-46D9-9D15-9D59E8C47118" targetRef="UpdateIntrumentStatusToError"/>
        <sequenceFlow id="sid-E405AE84-E015-4AB8-BFEB-502A804D39C9" isImmediate="true" name="" sourceRef="UpdateAnalysisStateToScheduled" targetRef="MonitoringInstrumentStatusChange"/>
        <sequenceFlow id="sid-CF3B924A-46FC-40E6-BC4A-285AE0CC9C4C" isImmediate="true" name="" sourceRef="UserConfirmVial" targetRef="DoesUserContinue"/>
        <sequenceFlow id="sid-06C49699-C486-4287-8753-6D4631760D1E" isImmediate="true" name="" sourceRef="AutomaticInstrumentSelection" targetRef="UserConfirmVial"/>
        <sequenceFlow id="sid-BAF33379-610C-4603-8BE9-F61BDBDB3D49" isImmediate="true" name="" sourceRef="MonitoringInstrumentStatusChange" targetRef="InstrumentsCheckup">
            <extensionElements>
                <activiti:executionListener class="com.persistent.greenlab.workflow.scheduler.MonitorInstrumentFinishedExecutionListener"/>
            </extensionElements>
        </sequenceFlow>
        <sequenceFlow id="sid-16330616-A681-4C50-A56E-0D7824FF9C55" isImmediate="true" name="" sourceRef="ValidAnalysis" targetRef="IsValidCommand"/>
        <sequenceFlow id="sid-E5F8C44A-9D50-4054-A75A-03675C2A77BB" isImmediate="true" name="" sourceRef="InstrumentsCheckup" targetRef="IsInstrumentIdlePriorityOrder1"/>
        <sequenceFlow id="sid-442912D1-02D2-42A2-BDB4-D5ECBC843FFD" isImmediate="true" name="Yes" sourceRef="IsValidCommand" targetRef="InstrumentsCheckup">
            <conditionExpression id="sid-d02274f0-894a-41c1-88dc-39f9082a76b7" xsi:type="tFormalExpression"> ${IsValidCommand==true}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-55B0D7CE-0A83-4D9C-94C0-6EADBC5F311A" isImmediate="true" name="" sourceRef="sid-2A87A051-E234-42DC-B153-6FFE5739D8AE" targetRef="IsThereAtLeastOneInstrumentOK"/>
        <sequenceFlow id="sid-7AF88DEA-00C9-40F8-9725-5DB1925388A1" isImmediate="true" name="Yes" sourceRef="IsInstrumentInError" targetRef="sid-6C7071D6-CE99-46D9-9D15-9D59E8C47118">
            <conditionExpression id="sid-ac14e665-709d-45cf-bc31-0dc7078dc50b" xsi:type="tFormalExpression"> ${IsInstrumentInError==true}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-521E196C-F674-443B-8439-A6A4F873507C" isImmediate="true" name="" sourceRef="sid-CDB70F30-11B7-4936-917A-60C48CBB17D7" targetRef="UpdateInstrumentStatusIdlToRunning"/>
        <sequenceFlow id="sid-DFFBD589-C235-4A9E-AEFD-FEECEDB28D75" isImmediate="true" name="" sourceRef="sid-54E7C57C-4100-4318-9359-C398FC3FCDBD" targetRef="UpdateInstrumentRunningToIdle"/>
        <sequenceFlow id="sid-73440689-B306-4AAA-8B5C-E865886AAAC5" isImmediate="true" name="" sourceRef="UpdateInstrumentRunningToIdle" targetRef="sid-270AAB82-043E-4B33-96F3-E8B09651C221"/>
        <sequenceFlow id="sid-3DA1F847-D44C-4972-93B8-2E76F2D0E4F8" isImmediate="true" name="Yes" sourceRef="IsThereAtLeastOneInstrumentOK" targetRef="AutomaticInstrumentSelection">
            <conditionExpression id="sid-8fdb2d9e-9161-4dae-9dd4-333b24a527b3" xsi:type="tFormalExpression"> ${IsThereAtLeastOneInstrumentOK==true}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-826DEFCA-04C2-4781-A783-3FE4CC0BF8A5" isImmediate="true" name="" sourceRef="sid-6C7071D6-CE99-46D9-9D15-9D59E8C47118" targetRef="sid-67D25F92-398D-4020-A0CD-BA527395F9B5"/>
        <sequenceFlow id="sid-EA0D402C-EB86-481B-BD52-FF8D201E9F37" isImmediate="true" name="" sourceRef="sid-54E7C57C-4100-4318-9359-C398FC3FCDBD" targetRef="UpdateAnalysisStateInProgressToEnded"/>
        <sequenceFlow id="sid-1A88D597-C65D-493F-BDE4-35B36CA3BB34" isImmediate="true" name="No" sourceRef="IsValidCommand" targetRef="EndEventInvalidCommand">
            <conditionExpression id="sid-6941bb0b-3c3c-4675-acb6-e7d230e40ea9" xsi:type="tFormalExpression"> ${IsValidCommand==false}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-BD22C095-E7E8-48B3-A8B8-77D671C40354" isImmediate="true" name="" sourceRef="UpdateIntrumentStatusToError" targetRef="sid-2A87A051-E234-42DC-B153-6FFE5739D8AE"/>
        <sequenceFlow id="sid-FA00DF1B-6B7E-42F1-8439-AA2E62EAE606" isImmediate="true" name="Yes" sourceRef="DoesUserContinue" targetRef="UpdateXMLPartOtherInstrument">
            <conditionExpression id="sid-7416ab38-9047-4306-85ef-97e64c8b0c40" xsi:type="tFormalExpression"> ${!empty VialNumber}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-6E601F06-BBF8-4708-8EF0-4FD1D95C8A03" isImmediate="true" name="No" sourceRef="IsThereAtLeastOneInstrumentOK" targetRef="UpdateAnalysisStateToError">
            <conditionExpression id="sid-c8545b25-dcc0-4aa8-bec0-7894c4906f6f" xsi:type="tFormalExpression"> ${IsThereAtLeastOneInstrumentOK==false}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-FF527D19-F32D-4D49-87C3-F638838885C2" isImmediate="true" name="" sourceRef="UpdateXMLPartOtherInstrument" targetRef="InstrumentsCheckup"/>
        <sequenceFlow id="sid-BA416BE3-A5CD-4DA2-8006-90A43264F265" isImmediate="true" name="" sourceRef="UpdateInstrumentStatusIdlToRunning" targetRef="sid-3B14D52E-5449-44B9-B344-68EB68793C39"/>
        <sequenceFlow id="sid-F79DE1A4-EFD9-44EF-87CE-8C662658DCA1" isImmediate="true" name="" sourceRef="sid-3B14D52E-5449-44B9-B344-68EB68793C39" targetRef="MonitoringAnalysis"/>
        <sequenceFlow id="sid-25CA92FA-094F-4789-8932-887E6B7EF165" isImmediate="true" name="" sourceRef="UpdateAnalysisStateToInProgress" targetRef="sid-3B14D52E-5449-44B9-B344-68EB68793C39"/>
        <sequenceFlow id="sid-E54E2C94-5D7C-485A-96C6-7D9E4228A7CB" name="" sourceRef="MonitoringAnalysis" targetRef="GateWayRunFinished"/>           
        <sequenceFlow id="sid-A63C7EFD-8B52-45D8-A74C-074528E3CF24" name="Yes" sourceRef="GateWayRunFinished" targetRef="sid-54E7C57C-4100-4318-9359-C398FC3FCDBD">
  <conditionExpression id="RunIsFinished" xsi:type="tFormalExpression"> ${RunIsFinished==true}</conditionExpression>
        </sequenceFlow>
        <sequenceFlow id="sid-C4543058-915D-45C9-A15C-5F27B4AD16E1" name="" sourceRef="TimerWaitingEndOfRun" targetRef="MonitoringAnalysis"/>
        <sequenceFlow id="sid-A4EB997B-29B6-4590-B229-6EB28D010183" name="No" sourceRef="GateWayRunFinished" targetRef="TimerWaitingEndOfRun">
            <conditionExpression id="RunIsNotFinished" xsi:type="tFormalExpression"> ${RunIsFinished==false}</conditionExpression>
        </sequenceFlow> 
    </process>

[jbarrez]

JavaDelegate is an interface, so how could you write something like:

public class MySecondServiceTaskDelegate extends JavaDelegate

Did you mean implements there?

Secondly, when both service tasks run in the same jvm, the static value shouldn't be null …

[sor1]

Sorry, yes, I mean implements.

I do not know if both service tasks run in the same jvm:
My process is executed by an external jar that is reponsible to start the process. The 2 delegate are defined in a same jar file.
The first task is synchrone, and the second task is asynchrone. If the second task is asynchrone, does that mean it is done in another jvm?

My tests seems to show that the same JVM is running for all the process: in the process list of the windows task manager, I can see one single java.exe corresponding to the jar responsible of starting the processes.
I can see that my problem (static variable set to null) happens after going throw an intermediateCatchEvent (timer), maybe this can help to understand the problem.

[frederikherema1]

How does your singleton-code look?

[sor1]

Thanks for spending time on this problem.
See at the beginning of this topic, this is explained: this is very simple (static class and static member). I cannot use the singleton pattern (with a getInstance() method that would re-create my object if it is null) because I really need to re-use my object (created in the first service task) in the second service task.

[jbarrez]

Then I got no clue what goes wrong … could you create a simple unit test demonstrating the problem, with a minimal bpmn 2.0 xml?

[sor1]

OK, I have to send a simple prototype. I am starting immediatly but it will take sometimes. Thanks.

[sor1]

To reproduce the problem:
1)Have a simple process with a timer set to PT30S between the 2 service tasks: Start–>FirstTask–>Timer–>SecondTask–> End.
2)And the static member manipulation explained above.
3)Have a jar file responsible of starting the process: so it does this kind of code: activitiRuntimeService.startProcessInstanceByKey("MySimpleProcess");
4)Activiti Explorer is deployed on tomcat and the tomcat service is started.

Result:
In the second task, you have a java.lang.NullPointerException because the static object is null.
If now I stop the tomcat server, I do not have the exception and the process ends successfully.

My interpretation is that Activiti Explorer takes the responsibility to continue the process after the timer (according to the Activiti database content). So in its JVM, of course the static member was not initialized.
If an expert could confirm this interpretation I would appreciate.

Thanks.