Converged Application Server is a multi-threaded application server that carefully manages resource allocation, concurrency, and thread synchronization for the modules it hosts. To obtain the greatest advantage from the Converged Application Server architecture, make use of the Converged Application Server concurrency utilities as described in "SIP Servlet Concurrency".

If an application needs to access the Future object of a task that belongs to a SIP application session that is not the current SIP application session, create a non-scheduled managed task to access it. For more information about submitting a task with a different application session as its context, see "Specifying Application Session Programmatically".

For scheduled managed tasks, applications should always access future objects from the SIPApplicationSession interface so that they get consistent access to a task's state across the cluster. This approach is highly recommended if a task needs to be cancelled so as to avoid a locally-stored reference. Cancellation of a running task, using the Future or ScheduledFuture object, in interrupted mode does not always guarantee that the task is aborted. See the description of the cancel method in:

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Future.html

Customers should use appropriate concurrency modes based on their application needs so that messages and/or timers belonging to the same Sip application session do not lead to concurrency access issues, such as race conditions or deadlocks. Converged Application Server employs its own locking framework based on the chosen concurrency mode. Discrete multiple operations associated with the same Sip Application session may lead to multiple lock-and-unlock routines. Such a situation should be avoided by combining these operations into a single non-scheduled managed task for that SIP application session.

Avoid nested lock situations. However, when applications employ nested SIP Application Session locks, the application logic associated with managing these locks must be designed with great care. Sometimes and in special circumstances, a nested SIP Application Session lock may lead to a deadlock. In such a situation, enabling the wlss.concurrent debug flag in the Converged Application Server Administration Console can assist you in your attempts to troubleshoot the issue. For information about setting the debug flag in Converged Application Server, see Converged Application Server Administrator's Guide.