linking fd to pipe identity via socket option

src/session_base.cpp

@@ -353,7 +353,8 @@ void zmq::session_base_t::process_attach (i_engine *engine_)
         //  Remember the local end of the pipe.
         zmq_assert (!pipe);
         pipe = pipes [0];
-
+        // Store engine assoc_fd for lilnking pipe to fd 
+        pipe->assoc_fd=engine_->get_assoc_fd();
         //  Ask socket to plug into the remote end of the pipe.
         send_bind (socket, pipes [1]);
     }