Fix another degradation, CPU maxes out when POLLOUT is set because poll exits on…

Fix another degradation, CPU maxes out when POLLOUT is set because poll exits on POLLOUT and doesn't wait for POLLIN.

src/proxy.cpp

@@ -108,11 +108,15 @@ int zmq::proxy (
     int more;
     size_t moresz;
     zmq_pollitem_t items [] = {
-        { frontend_, 0, ZMQ_POLLIN | ZMQ_POLLOUT, 0 },
-        { backend_, 0, ZMQ_POLLIN | ZMQ_POLLOUT, 0 },
+        { frontend_, 0, ZMQ_POLLIN, 0 },
+        { backend_, 0, ZMQ_POLLIN, 0 },
         { control_, 0, ZMQ_POLLIN, 0 }
     };
     int qt_poll_items = (control_ ? 3 : 2);
+    zmq_pollitem_t itemsout [] = {
+        { frontend_, 0, ZMQ_POLLOUT, 0 },
+        { backend_, 0, ZMQ_POLLOUT, 0 }
+    };
 
     //  Proxy can be in these three states
     enum {
@@ -127,6 +131,12 @@ int zmq::proxy (
         if (unlikely (rc < 0))
             return -1;
 
+        //  Get the pollout separately because when combining this with pollin it maxes the CPU
+        //  because pollout shall most of the time return directly
+        rc = zmq_poll (&itemsout [0], 2, 0);
+        if (unlikely (rc < 0))
+            return -1;
+
         //  Process a control command if any
         if (control_ && items [2].revents & ZMQ_POLLIN) {
             rc = control_->recv (&msg, 0);
@@ -160,7 +170,7 @@ int zmq::proxy (
         //  Process a request
         if (state == active
         &&  items [0].revents & ZMQ_POLLIN
-        &&  items [1].revents & ZMQ_POLLOUT) {
+        &&  itemsout [1].revents & ZMQ_POLLOUT) {
             rc = forward(frontend_, backend_, capture_,msg);
             if (unlikely (rc < 0))
                 return -1;
@@ -168,7 +178,7 @@ int zmq::proxy (
         //  Process a reply
         if (state == active
         &&  items [1].revents & ZMQ_POLLIN
-        &&  items [0].revents & ZMQ_POLLOUT) {
+        &&  itemsout [0].revents & ZMQ_POLLOUT) {
             rc = forward(backend_, frontend_, capture_,msg);
             if (unlikely (rc < 0))
                 return -1;