Called (usually by the FLUSH protocol), as an indication that the member should stop sending messages. Any messages sent after returning from this callback might get blocked by the FLUSH protocol. When the FLUSH protocol is done, and messages can be sent again, the FLUSH protocol will simply unblock all pending messages. If a callback for unblocking is desired, implement org.jgroups.ExtendedMembershipListener#unblock(). Note that block() is the equivalent of reception of a BlockEvent in the pull mode.