LinearExecutor uses an instance variable "command" to enqueue a command to be executed. It starts a new thread to read this variable and perform the command. A subsequent call to the "execute()" method without the processor thread being fully started will lead to an IAE.
ILW = HLM
I = H: It will crash the application with IAE
L = L: One needs to call the "execute()" methods in very rapid succession
W = M: One can provide his own implementation of the ClientNotifForwarder executor (via the "jmx.remote.x.fetch.notifications.executor" key in the provided env map)