check with jps that the pid file contains a pid that actually is an elasticsearch process

relates to #12063

dev-tools/src/main/resources/ant/integration-tests.xml

@@ -227,6 +227,27 @@
 
       <extract-pid file="@{es.pidfile}" property="integ.pid"/>
       <echo>Shutting down external node PID ${integ.pid}</echo>
+      <!-- verify with jps that this actually is the correct pid.
+      See if we can find the line "pid org.elasticsearch.bootstrap.Elasticsearch" in the output of jps -l.-->
+      <exec executable="jps">
+        <arg value="-l"/>
+        <redirector outputproperty="jps.pid.line">
+          <outputfilterchain>
+            <linecontains>
+              <contains value="${integ.pid} org.elasticsearch.bootstrap.Elasticsearch"/>
+            </linecontains>
+          </outputfilterchain>
+        </redirector>
+      </exec>
+      <fail
+          message="pid file at @{es.pidfile} is ${integ.pid} but jps -l did not report any process with org.elasticsearch.bootstrap.Elasticsearch and this pid.
+          Did you run mvn clean? Maybe an old pid file is still lying around.">
+        <condition>
+          <not>
+            <isset property="jps.pid.line"/>
+          </not>
+        </condition>
+      </fail>
 
       <exec executable="taskkill" failonerror="true" osfamily="winnt">
         <arg value="/F"/>
@@ -279,8 +300,6 @@
     <startup-elasticsearch/>
   </target>
 
-  <!-- TODO, for some more safety, add back some of the old jps logic
-       and verify the pid is really an ES process! (fail otherwise) -->
   <target name="stop-external-cluster" if="integ.pidfile.exists">
     <stop-node/>
   </target>