Why you need the process instance id of child / parent? That is your use case?
In my project I need the relation between child and parent process instance for process monitoring. There is no api to get this information but I could create a process event listener for my case. After the re-usable sub process node is triggered the process instance id of sub-process store in the sub-process node. The listener read this information and store it for application.
@Override
public void afterNodeTriggered(ProcessNodeTriggeredEvent event)
{
if (event.getNodeInstance() instanceof SubProcessNodeInstance)
{
long processInstanceId = event.getProcessInstance().getId();
SubProcessNodeInstance subProcessNodeInstance = (SubProcessNodeInstance) event.getNodeInstance();
long subProcessInstanceId = subProcessNodeInstance.getProcessInstanceId();
SubProcessNode subProcessNode = (SubProcessNode) event.getNodeInstance().getNode();
String subProcessId = subProcessNode.getProcessId();
String subProcessVersion = processInstanceManager.getProcessInstance(subProcessInstanceId)
.getProcess().getVersion();
String nodeName = subProcessNode.getName();
// store information
}
}
It works but it would be much better with api access.