Each time you create an ejb-timer (m_sessionContext.getTimerService().createTimer(...)), a new thread is created (Threadgroup JBoss, name "Timer-x", where x is a number).

But these threads are never terminated. This happens at least, if the timer has a timeout of 0, even if you explicitely cancel the timer in the ejbTimeout-event (we did not test, if there is the same problem for timers with a timeout > 0).

=> each canceled timer there is a Thread with state WAITING (which requires 400k stack-space by default).