When following this doc page to run rules engine in active mode
https://docs.jboss.org/drools/release/6.5.0.Final/drools-docs/html/ch07.html#d0e7301

If application code opens another thread and do ksession.insert(fact) then it's possible to have threading issues.

https://access.redhat.com/solutions/3645752

Requesting to add suggestion to highlight "ThreadSafeTrackableTimeJobFactoryManager" should be used in multithreading environment, code example:
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KieSessionConfiguration kconf = KnowledgeBaseFactory.newKnowledgeSessionConfiguration();
((org.drools.core.SessionConfiguration)kconf).setTimerJobFactoryType( TimerJobFactoryType.ok );
KieSession ksession = kContainer.newKieSession("ksession-name", kconf);
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Following code change has been made to update the default implementation to use ThreadSafeTrackableTimeJobFactoryManager :
https://github.com/kiegroup/drools/commit/92623e2435401db4f80eaf5e3e804c13ac776c0d