The problem was discussed with Emmanuel Lecharny in mail lists:
If you compare OrderedThreadPoolExecutor and standard ThreadPoolExecutor, you can see that ThreadPoolExecutor has useful params:
- core pool size
- maximum pool size
- work queue size
If you use unbounded thread pools and queues with mina Acceptor or Connector, you may get OutOfMemoryError under critical load because Java creates too many threads.
With ThreadPoolExecutor you may limit the number of threads (maximumPoolSize) and use a bounded queue (ex. LinkedBlockingQueue of limited capacity).
Unfortunately, this does not work with OrderedThreadPoolExecutor -both "waitingSessions" and "sessionTasksQueue" do not allow to configure their size nor pass a different queue implementation.
Even though OrderedThreadPoolExecutor extends ThreadPoolExecutor, it overrides the behavior significantly - seems that its meaning of "corePoolSize" and "maximumPoolSize" is different.