question: public Set addMembershipListenerAndAdviseGeneric ( MembershipListener listener ) { initializationGate ( ) ; membershipListeners . putIfAbsent ( listener , Boolean . TRUE ) ; return adviseGeneric ( ) ; }
target:  Atomically add listener to the list to receive notification when a *new* profile is added or a profile is removed, and return adviseGeneric(). This ensures that no membership listener calls are missed, but there is no guarantee that there won't be redundant listener calls.