public synchronized void release() {
            if( received ) {
                return;
            }
            // Else signal an error for the callers
            this.error = "Closing connection";
            this.received = true;
        }
Sort of like a Future, holds a locked reference to a response
 until the remote call has completed and returned a response.
jme3-networking/src/main/java/com/jme3/network/service/rpc/RpcConnection.java