You don't have to do anything for that. Maybe we should document that 😉
Activiti uses optimistic locking on the DB to deal with concurrency. So it leverages the DB capabilities for the hard work of concurrency control. DB's are optimised for that. That works just the same from 2 threads from the same ProcessEngine as from 2 threads on different ProcessEngines on different machines. It's most efficient if you configure the JobExecutor only on one machine. That prevents that multiple JobExecutors compete for the same jobs resulting in unnecessary optimistic locking failures.
But we don't have a lot of QA/CI for this yet. We only tested proper operation of the optimistic locking exceptions by controlling individual threads from the unit test thread. We hope to expand this soon to full load and stress testing.
If you experiment with this, let us know your findings.
