[GSS] (6.4.z) ProcessInstance is not correctly persisted when loaded with readOnly = true early in the same transaction

With conditions below:

• Parent/Sub process
• Tx1
  • Start a parent process instance
  • Sub process is started by CallActivity
  • Reached to a Human Task in the sub process. Tx Committed
• Tx2
  • Load the parent process with getProcessInstance(parentProcessInstanceId, true) // readOnly = true
  • Complete the Task in the sub process
  • Sub process is completed
  • Parent process instance is resumed
  • Reached to a Human Task in the parent process. Tx Committed

Parent ProcessInstance is not correctly persisted at the last step. For example, process variable is not updated.

Analysis
By debugging, I found that:

• If you load a process instance with readOnly = true for the first time in the transaction, it will be stored in JPAProcessInstanceManager.processInstances
• Then, if the same process instance is loaded with readOnly = false (e.g. a parent process instance is signaled on sub process completion), JPAProcessInstanceManager.getProcessInstance() will find the processInstance from "processInstances" cache.
• processInstance.isPersisted() is false at that moment. So TransactionManagerHelper.addToUpdatableSet() is not called

https://github.com/kiegroup/jbpm/blob/6.5.x/jbpm-persistence-jpa/src/main/java/org/jbpm/persistence/processinstance/JPAProcessInstanceManager.java#L111-L127

• So the process instance is not listed in "toBeUpdated" in TriggerUpdateTransactionSynchronization.beforeCompletion() so ProcessInstanceInfo.transform() is not called.

https://github.com/kiegroup/drools/blob/6.5.x/drools-persistence-jpa/src/main/java/org/drools/persistence/TriggerUpdateTransactionSynchronization.java#L36