ProcessInstanceInfo set start date when constructed

In the `PrometheusProcessEventListener`, the field `startDate` from a `processInstance` is used to time the process instance duration metric.
https://github.com/kiegroup/droolsjbpm-integration/blob/4fb9e4c239dfc21ea99ea5b701877cafeafcbe1d/kie-server-parent/kie-server-services/kie-server-services-prometheus/src/main/java/org/kie/server/services/prometheus/PrometheusProcessEventListener.java#L96

However, the start date was always null because it is being set when `getProcessInstance` is first called.
Since `getProcessInstance` is not called before we trigger the event listener, the start date was never set.
The `ProcessInstance` start date should be set when the `ProcessInstanceInfo` object is first created.

jbpm-persistence/jbpm-persistence-jpa/src/main/java/org/jbpm/persistence/processinstance/ProcessInstanceInfo.java

@@ -55,6 +55,7 @@
 import org.jbpm.marshalling.impl.ProtobufRuleFlowProcessInstanceMarshaller;
 import org.jbpm.persistence.api.PersistentProcessInstance;
 import org.jbpm.process.instance.impl.ProcessInstanceImpl;
+import org.jbpm.workflow.instance.WorkflowProcessInstance;
 import org.jbpm.workflow.instance.impl.WorkflowProcessInstanceImpl;
 import org.kie.api.runtime.Environment;
 import org.kie.api.runtime.process.ProcessInstance;
@@ -103,6 +104,16 @@ public ProcessInstanceInfo(ProcessInstance processInstance) {
         this.processInstance = processInstance;
         this.processId = processInstance.getProcessId();
         startDate = new Date();
+
+        // If we are creating a second Process Instance Info for the same process instance,
+        // it should not generate a new start date
+        if (this.processInstance != null) {
+            if (((WorkflowProcessInstanceImpl) this.processInstance).getStartDate() == null) {
+                ((WorkflowProcessInstanceImpl) processInstance).internalSetStartDate(this.startDate);
+            } else {
+                startDate = ((WorkflowProcessInstanceImpl) this.processInstance).getStartDate();
+            }
+        }
     }
 
     public ProcessInstanceInfo(ProcessInstance processInstance,

jbpm-persistence/jbpm-persistence-jpa/src/test/java/org/jbpm/persistence/map/impl/MapPersistenceTest.java

@@ -272,15 +272,18 @@ public void processWithNotNullStartDateTest() {
         KieBase kbase = createKieBase(process);
         StatefulKnowledgeSession crmPersistentSession = createSession(kbase);
 
-        RuleFlowProcessInstance processInstance = (RuleFlowProcessInstance) crmPersistentSession.startProcess( processId );   
+        RuleFlowProcessInstance processInstance = (RuleFlowProcessInstance) crmPersistentSession.startProcess( processId );
+
+        // Ensure the Process Instance Start Date is set immediately when the processInstanceInfo is created
+        Assert.assertNotNull(processInstance.getStartDate());
+
         InternalKnowledgeRuntime kruntime = processInstance.getKnowledgeRuntime();
         Assert.assertEquals( ProcessInstance.STATE_ACTIVE,
                              processInstance.getState() );
 
         ProcessInstanceInfo processInstanceInfo = new ProcessInstanceInfo(processInstance);
         processInstance = (RuleFlowProcessInstance) processInstanceInfo.getProcessInstance(kruntime, crmPersistentSession.getEnvironment());
 
-        Assert.assertNotNull(processInstance.getStartDate());
         Assert.assertEquals(processInstance.getStartDate(), processInstanceInfo.getStartDate());
     }