Candlepin gets stuck during startup forever, logging huge thread dump to error.log

Issue

• having problems to send messages to qpidd in past, such that candlepin was in Suspended mode
• resolving the issues with qpidd broker / katello_event_queue / ListenOnCandlepinEvents task
• restarting tomcat to restore candlepin fails after few minutes, logging huge thread dump to /var/log/candlepin/error.log
• candlepin CPU utilization is extremely high, such as a few hundreds percent to thousands percent and all the "/rhsm" related passenger requests are stuck and queuing for extremely long time, such as 30 minutes to an hour.