topic Re: Very Simple Process with Timer Start Event throws Exception in Alfresco Archive

Very Simple Process with Timer Start Event throws Exception

ct1 — Thu, 28 Jun 2012 17:55:32 GMT

I am seeing the OptimisticLockingException that plagues my use of timers and boundary events.While trying to use a timer start event, I am getting the OptimisticLockingException.With this very simple process, I am just trying to start the process at a specified time and log via a script task that it

Re: Very Simple Process with Timer Start Event throws Exception

frederikherema1 — Fri, 29 Jun 2012 05:28:50 GMT

Hi, seems like there are 2 job-executors running:


 at org.activiti.engine.impl.jobexecutor.AcquireJobsRunnable.run(AcquireJobsRunnable.java:57)

Make sure there are not more activiti.cfg.xml-files on your class path if you are using the ProcessEngines.getDefaultProcessEngine() approach (explorer does this by default). Alternatively, you can try to specify the correct file to load instead of just using ProcessEngines.getDefaultProcessEngine…

Re: Very Simple Process with Timer Start Event throws Exception

ct1 — Fri, 29 Jun 2012 15:51:37 GMT

Thank you for reviewing my post.

Here is a little more information.

I looked in the Activiti Rest classpath for activiti.cfg.xml files and found only one.
(It was in the …webapps\activiti-rest\WEB-INF\classes directory.) Do you think
there could be one hidden in one of the .jar files?

I used Activiti Explorer to deploy the BPMN20.xml file below. Then signed out of Explorer.

I stopped Tomcat and restarted the entire workstation. This should have stopped any
Process Engines that were running.

Then I started the instance of Tomcat that has the activiti-rest.war file in its webapp directory.
Looking at the Log File below, it looks like two Job Executors were started. Does it look like that to you?
Do you still think this indicates the presence of multiple activiti.cfg.xml files?

When the timer start event was supposed to start, the exception was thrown, as before. The next task
in the process did run, even though the exception was thrown.

I do have a general question, in addition to the specific ones above. If the existance of multiple
ProcessEngines causes a Timer Start Event to throw this exception, would the exception also
be thrown when I have another application that completes tasks in another BPMN process while
this Timer Start Event is waiting to start?

Log file when starting Tomcat:

Jun 29, 2012 8:57:41 AM org.activiti.engine.ProcessEngines initProcessEnginFromResource
INFO: initializing process engine for resource file:/C:/Workflow/Tomcat/apache-tomcat-7.0.27/webapps
/activiti-rest/WEB-INF/classes/activiti.cfg.xml

http://www.slf4j.org/codes.html#StaticLoggerBinder

Jun 29, 2012 8:57:43 AM org.activiti.engine.impl.ProcessEngineImpl <init>
INFO: ProcessEngine default created <<<<<<<<<<<<<<<<<<<<<<<<< ——— One ProcessEngine created???
Jun 29, 2012 8:57:43 AM org.activiti.engine.impl.jobexecutor.JobExecutor start
INFO: Starting up the JobExecutor[org.activiti.engine.impl.jobexecutor.DefaultJobExecutor].
Jun 29, 2012 8:57:43 AM org.activiti.engine.ProcessEngines initProcessEnginFromResource
INFO: initialised process engine default
Jun 29, 2012 8:57:43 AM org.activiti.engine.impl.jobexecutor.AcquireJobsRunnable run

INFO: Loading XML bean definitions from URL [file:/C:/Workflow/Tomcat/apache-tomcat-7.0.27/webapps/a
ctiviti-rest/WEB-INF/classes/activiti-context.xml]

Jun 29, 2012 8:57:43 AM org.activiti.engine.impl.ProcessEngineImpl <init>
INFO: ProcessEngine default created <<<<<<<<<<<<<<<<<<<<<<<<< ————- Second ProcessEngine created??????
Jun 29, 2012 8:57:43 AM org.activiti.engine.impl.jobexecutor.JobExecutor start
INFO: Starting up the JobExecutor[org.activiti.engine.impl.jobexecutor.DefaultJobExecutor].
Jun 29, 2012 8:57:43 AM org.activiti.engine.impl.jobexecutor.AcquireJobsRunnable run

The bpmn20.xml file:

http://www.omg.org/spec/BPMN/20100524/MODEL

http://www.w3.org/2001/XMLSchema-instance

http://activiti.org/bpmn

http://www.omg.org/spec/BPMN/20100524/DI

http://www.omg.org/spec/DD/20100524/DC

http://www.omg.org/spec/DD/20100524/DI

http://www.w3.org/2001/XMLSchema

http://www.w3.org/1999/XPath

http://www.activiti.org/test

Contents of the webapps directory. Several of the Projects contain activiti.cfg.xml files, but
activiti-rest would not be looking in any of them for a cfg file, would it?

For information, here are the contents of the directory containing the activiti.cfg.xml file:

Thank you.

Re: Very Simple Process with Timer Start Event throws Exception

frederikherema1 — Mon, 02 Jul 2012 12:32:11 GMT

Activiti-explorer uses a separate "java" engine than the REST-webapp… If you point the two configs to the same database, they'll play nicely together.

Re: Very Simple Process with Timer Start Event throws Exception

ct1 — Mon, 02 Jul 2012 13:29:49 GMT

Thank you.

That is good news. So it is alright to have multiple ProcessEngines pointing to the same database.

However, it does not seem to speak to my situation. I have both REST and Explorer configured to point to the same database, and both deployed in the same instance of Tomcat.

I am only starting the instance of Tomcat that has the activiti-explorer.war and the activiti-rest.war in its webapp directory. I do not attempt to use either Activiti Explorer or the REST interface in any application. The only action anticipated is that the timer start event defined as the first task in a process will start at the specified time and the process will continue until it hits a wait state, in this case, the end event. Instead of running cleanly, the timer start event seems to cause an exception.

Should this happen? If not, what should I do to prevent it?

Thank you again.

Re: Very Simple Process with Timer Start Event throws Exception

frederikherema1 — Mon, 02 Jul 2012 13:36:15 GMT

Since 2 engine's are running, 2 job-executors are active by default. One of them a quires the job together with the second one. The first one will execute the job successfully. The second one, unaware of the job being acquired already (transactions overlap) will execute also and get an exception. This is intended to work this way. The second "execute" is rolled back. So you timer fires correctly and the second job-executor execution is a no-op (due to the rollback).

This is fine when you system integrates with the activiti transactions (or the other way around). The only downside is that you get these exceptions? To overcome this, you can disable the job-executor in one of the engines. This way, only one engine (eg. webapp-rest) is responsible for all timer and async-related operations.

Re: Very Simple Process with Timer Start Event throws Exception

ct1 — Mon, 02 Jul 2012 14:06:58 GMT

Thank you.

Your response really made this much clearer. So, I should put

<property name="jobExecutorActivate" value="false" />
in the activiti.cfg.xml file in the …/webapps/activiti-explorer/WEB-INF/classes directory?

The, all processes with a timer start event or a timer boundary event will be handled by the Job
Executor defined in the activiti.cfg.xml file in the …activiti-rest/WEB-INF/classes directory. Right?

Thank you.

Re: Very Simple Process with Timer Start Event throws Exception

frederikherema1 — Mon, 02 Jul 2012 14:33:28 GMT

spot on!

Re: Very Simple Process with Timer Start Event throws Exception

ct1 — Tue, 03 Jul 2012 14:54:35 GMT

I am trying your solution.

I turned off the jobExecutorActivate (set to "false") in the …\webapps\activiti-explorer\WEB-INF\classes\activiti.cfg.xml file, stopped Tomcat, started Tomcat, used Explorer to redeploy the BPMN20.xml file containing the timer start event. I then logged off Explorer and waited for the timer start event to execute. The exception was thrown again.

I have several applications deployed on that instance of Tomcat that use ProcessEngines. I will next remove each of their war files from the webapps directory and delete the application directories that Tomcat created from each of them. Then I will try the timer start event again.

Related to the reply you gave above, do I need to be concerned that the …\webapps\activiti-rest\WEB-INF\classes\activiti-context.xml file has the property
'<property name="jobExecutorActivate" value="true" />'
in the bean id processEngineConfiguration? Will that create another JobExecutor? I was under the impression that when I use the activiti.cfg.xml to configure Activiti, that the activiti-context.xml would not be used, but I know I could be mistaken. Do I also need to set that to "false" also?

Thank you.

Re: Very Simple Process with Timer Start Event throws Exception

ct1 — Fri, 06 Jul 2012 21:23:11 GMT

Thank you for all your help getting to this point.

I am attempting to implement your suggestion by removing all applications, except activiti-rest, that might create a Job Executor from the Tomcat instance running activiti-rest.

I deployed the BPMN20 process that contains the timer start event using Activiti Explorer. Then I stopped Tomcat, removed the activiti-explorer directory from the …/webapps directory and then restarted Tomcat. I got the log shown below which seems to show two Process Engines created but only on JobExecutor started. The directory listing of the …/webapps directory is below, showing activiti-rest to be the only Activiti application deployed.

This is the log file when I restarted Tomcat:

INFO: initializing process engine for resource file:/C:/Workflow/Tomcat/apache-tomcat-7.0.27/webapps
/activiti-rest/WEB-INF/classes/activiti.cfg.xml

http://www.slf4j.org/codes.html#StaticLoggerBinder

INFO: ProcessEngine default created

<<<<<<<<—————-First Process Engine Starts

INFO: Starting up the JobExecutor[org.activiti.engine.impl.jobexecutor.DefaultJobExecutor].

<<<— Job Executor Starts

<<<<<<<—– Second Process Engine Starts

INFO: ProcessEngine default created

<<<<<<< —- No Second Job Executor started

…/webapps directory:

<<<<<<<<<<—- Only app with a JobExecutor

At the time the timer start event was configured to start, this was logged:

The timer start event ran as scheduled and did not throw an exception.

Now, my question is, is this a reasonable configuration (one instance of the activiti.cfg.xml file with the "JobExecutorActivate=true") considering that we may need instances of Tomcat running activiti-rest on multiple servers accessing the same database? If we run like that and the server that created the JobExecutor goes down, won't we then miss executing all the timer events scheduled for the time the JobExecutor is down?

Thank you again for helping.

Re: Very Simple Process with Timer Start Event throws Exception

frederikherema1 — Mon, 16 Jul 2012 08:00:38 GMT

THis is a reasonable approach for avoiding concurrency-exceptions on job-executors. However, enabling them all is fine as well, if you processes don do non-transactional stuff. If they do, they get rolled back cleanly and it seems like the second job executor never executed (only proof is execution-stacktrace).

Offcourse, if that one machine goes down, no jobs will be executed. I'm afraid you'll have to come up with a custom solution for this, activiti has nothing built-in for this.