Suspend Process Instance in JavaDelegate

Camunda 7 Topics Discussion & Questions
1

Dear Community,

I am trying to suspend a process instance in one of its service tasks. I did it like described in Camunda synchronous process instance wont suspend - Stack Overflow

However, doing it like that I get an optimistic locking exception. Apparently, when I suspend the process instance at the same time the process engine finishes the Java Delegate and wants to write that to the DB as well.

So, as a workaround I included a Thread#sleep for testing purposes. Now the process engine behaves funny. The Java Delegate repeats getting executed. Why is that?

The code of my JavaDelegate

@Service
public class SuspensionDelegate implements JavaDelegate {

	@Override
	public void execute(DelegateExecution execution) throws Exception {

		RuntimeService runtimeService = execution.getProcessEngineServices().getRuntimeService();

		String pid = execution.getProcessInstanceId();

		VariableMap variables = Variables//
				.createVariables()//
				.putValue("processInstanceToSuspend", pid);
		runtimeService.startProcessInstanceByKey("Process_Suspension", variables);

		System.out.println("Suspending Process Instance ...");

		runtimeService//
				.updateProcessInstanceSuspensionState()//
				.byProcessInstanceId(pid)//
				.suspend();

		Thread.sleep(5000);
	}
}

Any hint is appreciated.

2

Hi @philipp.hehnle,

Each JavaDelegateis executed by a job executor. A job that gets stuck, may prevent the completion of the process. Therefore, a timeout is implemented. This timeout is configurable via the property camunda.bpm.job-execution.lock-time-in-millis the default is 300000. Can it be, that the lock time is too restrictive?

3

I did not change this property. So, it should still be the default value.

4

Hi @philipp.hehnle,

Is your delegate called by a service task?
I assume that the following is happening:

  1. Your delegate is called
  2. You suspend the process
  3. You add the Thread sleep
  4. Your delegate completes BUT fails because its process instance has been suspended and completing a task would advance the token, which is an invalid operation for suspended processes. Since the delegate failed, the service task will be repeated.

You can try using a TaskListener or an ExecutionListener.

1 Like
5

Hi @StephanHaarmann,

I tried the same setup with an execution listener. I get the same result.

Your assumption seems plausible. Can you think of a way to get it working?

6

Hi @philipp.hehnle,

Below is a great simple example created by @Niall

Notice: “Suspend this instance” service task is synchronously executed.

2 Likes
7

@hassang Thank you for sharing the example.

However, I am not entirely getting the point of the thread. Niall states that you need to set async continuations in the process model. At those points the suspension can become effective.https://forum.camunda.io/t/suspending-a-process-instance-unconditionally/15325/16?u=philipp.hehnle

He does not say anything about the event subprocess. So, as far as I understand the fact that the suspension is triggered in an event subprocess should not have any influence. Am I right or am I missing something?

I set an async continuation before at the subsequent activity. However, the SuspensionDelegate keeps repeating itself.

8

You could “Message Throw” to a different process, with a message containing your process id.
This other process starts on “Message Receive” and suspends the process with the ID in the message.

9

Only make sure that you don’t set it for the SuspensionDelegate service task.

10

I believe using an event sub-process is required for the solution to work. Otherwise, suspension implementation will get in an infinite loop.

1 Like
11