Chapter 79 Exclusive Areas, RTI Connext Threads, and User Listeners

Connext Event and Receive threads may invoke user code through the Listener callbacks installed on different Entities while executing internal Connext code. In turn, user code inside the callbacks may invoke Connext APIs that reenter the internal code space of Connext. For thread safety, Connext allocates and uses mutual exclusion semaphores (mutexes).

As discussed in 18.8.8 Exclusive Areas (EAs), when multiple threads and multiple mutexes are mixed together, deadlock may result. To prevent deadlock from occurring, Connext is designed using careful analysis and following rules that force mutexes to be taken in a certain order when a thread must take multiple mutexes simultaneously.

However, because the Event and Receive threads already hold mutexes when invoking user callbacks, and because the Connext APIs that the user code can invoke may try to take other mutexes, deadlock may still result. Thus, to prevent user code to cause internal Connext threads to deadlock, we have created a concept called Exclusive Areas (EA) that follow rules that prevent deadlock. The more EAs that exist in a system, the more concurrency is allowed through Connext code. However, the more EAs that exist, the more restrictions on the Connext APIs that are allowed to be invoked in Entity Listener callbacks.

For a more detailed discussion on EAs and the restrictions on the use of Connext APIs within Entity Listener methods, please see 18.8.8 Exclusive Areas (EAs).