The previous code to block the socket from receiving on that pipe during a disconnect was vulnerable to a race condition. This code calls with the terminate functions of both ends of the pipe - I believe this should be safer. This required storing a pointer to the socket end of the pipe

src/session_base.hpp

@@ -103,6 +103,9 @@ namespace zmq
 
         //  Pipe connecting the session to its socket.
         zmq::pipe_t *pipe;
+        
+        //  Socket end of the pipe, for delay attach scenario
+        zmq::pipe_t *outpipe;
 
         //  This flag is true if the remainder of the message being processed
         //  is still in the in pipe.