Case found not covered in latest zmq::proxy() code.

src/proxy.cpp

@@ -66,6 +66,8 @@
     delete poller_receive_blocked;\
     delete poller_send_blocked;\
     delete poller_both_blocked;\
+    delete poller_frontend_only;\
+    delete poller_backend_only\
 
 
 #define CHECK_RC_EXIT_ON_FAILURE()\
@@ -173,14 +175,18 @@ int zmq::proxy (
 
     //  If frontend_==backend_ 'poller_send_blocked' and 'poller_receive_blocked' are the same, 'ZMQ_POLLIN' is ignored.
     //  In that case 'poller_send_blocked' is not used. We need only 'poller_receive_blocked'.
-    //  We also don't need 'poller_both_blocked', no need to initialize it.
+    //  We also don't need 'poller_both_blocked', 'poller_backend_only' nor 'poller_frontend_only' no need to initialize it.
     //  We save some RAM and time for initialization.
     zmq::socket_poller_t *poller_send_blocked = NULL;                    //  All except 'ZMQ_POLLIN' on 'backend_'.
     zmq::socket_poller_t *poller_both_blocked = NULL;                    //  All except 'ZMQ_POLLIN' on both 'frontend_' and 'backend_'.
+    zmq::socket_poller_t *poller_frontend_only = NULL;                   //  Only 'ZMQ_POLLIN' and 'ZMQ_POLLOUT' on 'frontend_'.
+    zmq::socket_poller_t *poller_backend_only = NULL;                    //  Only 'ZMQ_POLLIN' and 'ZMQ_POLLOUT' on 'backend_'.
 
     if (frontend_ != backend_) {
         poller_send_blocked = new (std::nothrow) zmq::socket_poller_t;   //  All except 'ZMQ_POLLIN' on 'backend_'.
         poller_both_blocked = new (std::nothrow) zmq::socket_poller_t;   //  All except 'ZMQ_POLLIN' on both 'frontend_' and 'backend_'.
+        poller_frontend_only = new (std::nothrow) zmq::socket_poller_t;  //  Only 'ZMQ_POLLIN' and 'ZMQ_POLLOUT' on 'frontend_'.
+        poller_backend_only = new (std::nothrow) zmq::socket_poller_t;   //  Only 'ZMQ_POLLIN' and 'ZMQ_POLLOUT' on 'backend_'.
         frontend_equal_to_backend = false;
     } else
         frontend_equal_to_backend = true;
@@ -222,6 +228,10 @@ int zmq::proxy (
         CHECK_RC_EXIT_ON_FAILURE ();
         rc = poller_receive_blocked->add (backend_, NULL, ZMQ_POLLIN | ZMQ_POLLOUT);  //  All except 'ZMQ_POLLIN' on 'frontend_'.
         CHECK_RC_EXIT_ON_FAILURE ();
+        rc = poller_frontend_only->add (frontend_, NULL, ZMQ_POLLIN | ZMQ_POLLOUT);
+        CHECK_RC_EXIT_ON_FAILURE ();
+        rc = poller_backend_only->add (backend_, NULL, ZMQ_POLLIN | ZMQ_POLLOUT);
+        CHECK_RC_EXIT_ON_FAILURE ();
     }
 
     //  Register 'control_' with pollers.
@@ -239,6 +249,10 @@ int zmq::proxy (
             CHECK_RC_EXIT_ON_FAILURE ();
             rc = poller_both_blocked->add (control_, NULL, ZMQ_POLLIN);
             CHECK_RC_EXIT_ON_FAILURE ();
+            rc = poller_frontend_only->add (control_, NULL, ZMQ_POLLIN);
+            CHECK_RC_EXIT_ON_FAILURE ();
+            rc = poller_backend_only->add (control_, NULL, ZMQ_POLLIN);
+            CHECK_RC_EXIT_ON_FAILURE ();
         }
     }
 
@@ -342,34 +356,50 @@ int zmq::proxy (
                         if (poller_wait == poller_both_blocked)
                             poller_wait = poller_send_blocked;
                         else
-                            if (poller_wait == poller_receive_blocked)
+                            if (poller_wait == poller_receive_blocked || poller_wait == poller_frontend_only)
                                 poller_wait = poller_in;
                     }
                     if (reply_processed) {   //  'backend_' -> 'frontend_'
                         if (poller_wait == poller_both_blocked)
                             poller_wait = poller_receive_blocked;
                         else
-                            if (poller_wait == poller_send_blocked)
+                            if (poller_wait == poller_send_blocked || poller_wait == poller_backend_only)
                                 poller_wait = poller_in;
                     }
                 }
             } else {
-                //  No requests have been processed, there were no 'ZMQ_POLLOUT' events.
-                //  That means that receiving end queue(s) is/are full.
-                //  Disable receiving 'ZMQ_POLLIN' for sockets for which there's no 'ZMQ_POLLOUT'.
+                //  No requests have been processed, there were no 'ZMQ_POLLIN' with corresponding 'ZMQ_POLLOUT' events.
+                //  That means that out queue(s) is/are full or one out queue is full and second one has no messages to process.
+                //  Disable receiving 'ZMQ_POLLIN' for sockets for which there's no 'ZMQ_POLLOUT',
+                //  or wait only on both 'backend_''s or 'frontend_''s 'ZMQ_POLLIN' and 'ZMQ_POLLOUT'.
                 if (frontend_in) {
-                    if (poller_wait == poller_send_blocked)
-                        poller_wait = poller_both_blocked;
-                    else
-                        poller_wait = poller_receive_blocked;
+                    if (frontend_out)
+                        // If frontend_in and frontend_out are true, obviously backend_in and backend_out are both false.
+                        // In that case we need to wait for both 'ZMQ_POLLIN' and 'ZMQ_POLLOUT' only on 'backend_'.
+                        // We'll never get here in case of frontend_==backend_ because then frontend_out will always be false.
+                        poller_wait = poller_backend_only;
+                    else {
+                        if (poller_wait == poller_send_blocked)
+                            poller_wait = poller_both_blocked;
+                        else
+                            if (poller_wait == poller_in)
+                                poller_wait = poller_receive_blocked;
+                    }
                 }
                 if (backend_in) {
                     //  Will never be reached if frontend_==backend_, 'backend_in' will
                     //  always be false due to design in 'for' event processing loop.
-                    if (poller_wait == poller_receive_blocked)
-                        poller_wait = poller_both_blocked;
-                    else
-                        poller_wait = poller_send_blocked;
+                    if (backend_out)
+                        // If backend_in and backend_out are true, obviously frontend_in and frontend_out are both false.
+                        // In that case we need to wait for both 'ZMQ_POLLIN' and 'ZMQ_POLLOUT' only on 'frontend_'.
+                        poller_wait = poller_frontend_only;
+                    else {
+                        if (poller_wait == poller_receive_blocked)
+                            poller_wait = poller_both_blocked;
+                        else
+                            if (poller_wait == poller_in)
+                                poller_wait = poller_send_blocked;
+                    }
                 }
             }