Error initializing flowable engine

1

My team is currently experiencing an issue where attempts to start the flowable engine builder fail with the following error:

java.lang.ClassCastException: class org.flowable.eventregistry.impl.cfg.StandaloneEventRegistryEngineConfiguration cannot be cast to class org.flowable.engine.ProcessEngineConfiguration (org.flowable.eventregistry.impl.cfg.StandaloneEventRegistryEngineConfiguration and org.flowable.engine.ProcessEngineConfiguration are in unnamed module of loader coldfusion.bootstrap.BootstrapClassLoader @7af52ec7)
at org.flowable.management.jmx.JMXConfigurator.configure(JMXConfigurator.java:119) ~[flowable-jmx-6.8.0.jar:6.8.0]
at org.flowable.common.engine.impl.AbstractEngineConfiguration.configuratorsAfterInit(AbstractEngineConfiguration.java:1120) ~[flowable-engine-common-6.8.0.jar:6.8.0]
at org.flowable.eventregistry.impl.EventRegistryEngineConfiguration.init(EventRegistryEngineConfiguration.java:255) ~[flowable-event-registry-6.8.0.jar:6.8.0]
at org.flowable.eventregistry.impl.EventRegistryEngineConfiguration.buildEventRegistryEngine(EventRegistryEngineConfiguration.java:207) ~[flowable-event-registry-6.8.0.jar:6.8.0]
at org.flowable.eventregistry.impl.configurator.EventRegistryEngineConfigurator.initEventRegistryEngine(EventRegistryEngineConfigurator.java:87) ~[flowable-event-registry-configurator-6.8.0.jar:6.8.0]
at org.flowable.eventregistry.impl.configurator.EventRegistryEngineConfigurator.configure(EventRegistryEngineConfigurator.java:64) ~[flowable-event-registry-configurator-6.8.0.jar:6.8.0]
at org.flowable.common.engine.impl.AbstractEngineConfiguration.configuratorsAfterInit(AbstractEngineConfiguration.java:1120) ~[flowable-engine-common-6.8.0.jar:6.8.0]
at org.flowable.engine.impl.cfg.ProcessEngineConfigurationImpl.init(ProcessEngineConfigurationImpl.java:1022) ~[flowable-engine-6.8.0.jar:6.8.0]
at org.flowable.engine.impl.cfg.ProcessEngineConfigurationImpl.buildProcessEngine(ProcessEngineConfigurationImpl.java:906) ~[flowable-engine-6.8.0.jar:6.8.0]

From the information our sysadmin helped dig up, this issue started occurring for us a few days ago (9/29) after our server restarted. We have not deployed/installed any updates to Flowable since updating to 6.8.0 in June, so it’s a bit odd that it’s decided to fail out of nowhere. Could this be a configuration file that was corrupted or edited improperly, or something more serious?

2

An update: We have resolved this issue, turned out to be a weird case of extremely precise bad timing.

When Flowable is first spinning up, it locks the schema down to prevent changes while it’s loading and then releases it once the connection has been made - but if you get extremely unlucky on timing with your server shutting down automatically, that lock never gets cleared.

The table in question where the lock is stored is FLW_EV_DATABASECHANGELOGLOCK. When it has LOCKED = 1, and LOCKGRANTED and LOCKEDBY not null, new connections get blocked - so if it gets stuck just set LOCKED to 0 and LOCKGRANTED and LOCKEDBY to null and it should be fine again.