putForExternalRead will certainly help, but only as an optimisation (i.e., the put in line 3 would be a putForExternalRead so it doesn't interfere with other readers) The check in line 1 will need to use some form of synchronisation/locking. I'd recommend looking at the Hibernate code base as a reference. http://fisheye.jboss.org/browse/Hibernate/trunk/Hibernate3 View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4050158#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...