If the server pool experiences failure while attempting to create or start a new runnable server for the pool, then the server pool attempts to shut down all threads in the pool and exits with an exception. Since the pool expansion is performed by the server pool thread, this type of failure can occur at any time, asynchronous to any call to start() or resize(). To detect this kind of failure, periodically test the completion state of the server pool or register a callback for the RW_THR_EXCEPTION state.