Serializing any amount of data while other threads might change that data entails the risk of creating an inconsistent snapshot. Mutual exclusion (locking) would be one way, but since there's no progress during this time anyway you might as well stop the session. If you have the memory, serialize to a byte[] and write this out to secondary storage after restarting. -W On 13 July 2012 03:23, chrisLi <shengtao0077(a)163.com&gt; wrote: