Since JDK 6, the RMI implementation (sun.rmi.runtime.RuntimeUtil) has used an instance of java.util.concurrent.ScheduledThreadPoolExecutor in order to execute activities with timed delays (this replaced use of a java.util.Timer in some cases and dedicated waiting threads in others). With the current implementation, however, the threads in this scheduled thread pool (by default only one), once they are created, never time out.

The Java SE 6 java.util.concurrent API does allow such threads to time out (without having to shut down the whole thread pool) with the use of the new ThreadPoolExecutor.allowCoreThreadTimeOut method, and the RMI implementation code actually has an invocation on that method, but it is currently commented out because at the time this RMI code was written, there were a couple of bugs that made using the allowCoreThreadTimeOut method on a ScheduledThreadPoolExecutor (in particular) problematic (6327342 and 6440728). These bugs were fixed in later builds of JDK 6, so therefore, it would be good to update the RMI implementation to actually use this feature to reduce the existence of unnecessary threads.