Sync entry methods are special in that calls to sync entry methods are blocking - they do not return control to the caller until the method is finished executing completely. Sync methods may have return values; however, they may only return messages.
Exclusive entry methods, which exist only on node groups, are entry methods that do not execute while other exclusive entry methods of its node group are executing in the same node. If one exclusive method of a node group is executing on node 0, and another one is scheduled to run on that same node, the second exclusive method will wait for the first to finish before it executes. To make an entry method exclusive, add the keyword exclusive to that entry method's attribute list.