Couldn't you use yield() to generate a context-switch? It would only happen in that spot, but should produce some good testing. -----Original Message----- From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Dean Jones Sent: Monday, July 16, 2007 5:48 AM To: Rules Users List Subject: Re: [rules-users] Rule compilation errors under heavy load On 7/14/07, Mark Proctor <mproctor(a)codehaus.org&gt; wrote: Okay, I've just converted the simple test that I added earlier to a Junit test. The test is not guaranteed to fail if there are thread safety errors, just very likely to fail (don't know if this is acceptable for you). Initially, I wrote a test which guaranteed that calls to the addPackage() and getPackage() methods were interleaved by different threads, but, annoyingly, this test passed. It seems that a context-switch halfway through one of these methods is necessary to provoke the problem (which is difficult to guarantee :-) Dean.