BaseServer.getConnection creates a socket and puts it in the shared map under a lock.

However it does not connect the socket inside the lock, so another thread calling getConnection at the same time can get the unconnected socket, which will throw a NPE when used because it's not connected yet (all the checks before returning and using it only look for isOpen, not isConnected).

java.lang.NullPointerException
at org.jgroups.blocks.cs.TcpConnection.doSend(TcpConnection.java:184)
at org.jgroups.blocks.cs.TcpConnection._send(TcpConnection.java:171)
at org.jgroups.blocks.cs.TcpConnection.send(TcpConnection.java:141)
at org.jgroups.blocks.cs.BaseServer.send(BaseServer.java:185)