Set the ZMQ Receive Buffer High Water Mark only if it changes (#444) (#445)

This is to reduce the impact of a bug present in ZMQ 4.2.0 and ZMQ 4.2.1
which led to a bad lwm and hwm calculation when ZMQ_RCVHWM was set after
the bind of the socket. See cppTango#444 for more details

Author: bourtemb

cppapi/client/eventconsumer.h

@@ -638,6 +638,7 @@ private :
 	void print_error_message(const char *mess) {ApiUtil *au=ApiUtil::instance();au->print_error_message(mess);}
 	void set_ctrl_sock_bound() {sock_bound_mutex.lock();ctrl_socket_bound=true;sock_bound_mutex.unlock();}
 	bool is_ctrl_sock_bound() {bool _b;sock_bound_mutex.lock();_b=ctrl_socket_bound;sock_bound_mutex.unlock();return _b;}
+	void set_socket_hwm(size_t hwm);
 
     bool check_zmq_endpoint(const string &);
 

cppapi/client/zmqeventconsumer.cpp

@@ -886,7 +886,7 @@ bool ZmqEventConsumer::process_ctrl(zmq::message_t &received_ctrl,zmq::pollitem_
 
             if (connect_pub == true)
             {
-                event_sub_sock->setsockopt(ZMQ_RCVHWM,&sub_hwm,sizeof(sub_hwm));
+                set_socket_hwm(sub_hwm);
 
                 event_sub_sock->connect(endpoint);
                 if (force_connect == 0)
@@ -3497,6 +3497,26 @@ void ZmqEventConsumer::get_subscribed_event_ids(DeviceProxy *_dev,vector<int> &_
     }
 }
 
+/**
+ *
+ * Set the ZMQ Receive Buffer High Water Mark only if it changes
+ * This is to reduce the impact of a bug present in ZMQ 4.2.0 and ZMQ 4.2.1
+ * which leads to a bad lwm and hwm calculation when ZMQ_RCVHWM is set after
+ * the bind of the socket. See cppTango#444 for more details
+ *
+ * @param hwm: new ZMQ receive buffer high water mark
+ */
+void ZmqEventConsumer::set_socket_hwm(size_t hwm)
+{
+    int current_sub_hwm = SUB_HWM;
+    size_t curr_sub_hw_size = sizeof(current_sub_hwm);
+    event_sub_sock->getsockopt(ZMQ_RCVHWM,&current_sub_hwm, &curr_sub_hw_size);
+    if(hwm != current_sub_hwm)
+    {
+        event_sub_sock->setsockopt(ZMQ_RCVHWM, &hwm, sizeof(hwm));
+    }
+}
+
 //--------------------------------------------------------------------------------------------------------------------
 //
 // method :