Jimmy, multiple agents will not access the variable simultaneously unless you have fired them in separate threads. In the standard MASON distribution, this is only possible via ParallelSequence or AsynchronousSteppable. So you'll need to be more specific about what you mean here. As to concurrent access control, Java does this like any other multithreaded system. Create a lock variable that both agents have access to -- perhaps an instance variable. An empty array works nicely: Object[] lock = new Object[0]; Then later your agents access the variable of choice like this: synchronized(lock) { // do stuff with my variable } Sean On Dec 25, 2006, at 3:28 PM, Jimmy Ong wrote: > Merry Christmas to all! > > Can someone show me how do i prevent concurrent access to some > variable > between 2 or more agents? I tried to synchronize on state.schedule > or an > arbitrary object, but it doesn't work. > > Thanks in advance, > Jim.