Change mutex used for EventSupplier::detect_change

Remove detect_mutex and protect detect_change method with
event_mutex to synchronize access to the old attribute value.

Fixes data race between:
* polling thread (EventSupplier::detect_and_push_xxx_event)
* and user thread pushing events (EventSupplier::detect_change)

This is a backport of 8d4a1bb from tango-9-lts.

Author: mliszcz

cppapi/server/attribute.cpp

@@ -4462,29 +4462,33 @@ void Attribute::fire_archive_event(DevFailed *except)
 		{
 
 //
-// Execute detect_change only to calculate the delta_change_rel and
-// delta_change_abs and force_change !
 //
 
 			bool force_change   = false;
 			bool quality_change = false;
 			double delta_change_rel = 0.0;
 			double delta_change_abs = 0.0;
 
-            if (event_supplier_nd != NULL)
-                event_supplier_nd->detect_change(*this, ad,true,delta_change_rel,delta_change_abs,except,force_change,dev);
-            else if (event_supplier_zmq != NULL)
-                event_supplier_zmq->detect_change(*this, ad,true,delta_change_rel,delta_change_abs,except,force_change,dev);
-
-
-			vector<string> filterable_names;
-			vector<double> filterable_data;
-			vector<string> filterable_names_lg;
-			vector<long> filterable_data_lg;
-
 			{
 				omni_mutex_lock oml(EventSupplier::get_event_mutex());
 
+				// Execute detect_change only to calculate the delta_change_rel and
+				// delta_change_abs and force_change !
+
+				if (event_supplier_nd || event_supplier_zmq)
+				{
+					EventSupplier* event_supplier = event_supplier_nd ? event_supplier_nd : event_supplier_zmq;
+					event_supplier->detect_change(
+					    *this,
+					    ad,
+					    true,
+					    delta_change_rel,
+					    delta_change_abs,
+					    except,
+					    force_change,
+					    dev);
+				}
+
 				if (except != NULL)
 				{
 					prev_archive_event.err    = true;
@@ -4521,6 +4525,11 @@ void Attribute::fire_archive_event(DevFailed *except)
 				prev_archive_event.inited = true;
 			}
 
+			vector<string> filterable_names;
+			vector<double> filterable_data;
+			vector<string> filterable_names_lg;
+			vector<long> filterable_data_lg;
+
 			filterable_names.push_back("forced_event");
 			if (force_change == true)
 				filterable_data.push_back((double)1.0);

cppapi/server/eventsupplier.cpp

@@ -1182,12 +1182,6 @@ bool EventSupplier::detect_change(Attribute &attr, struct SuppliedEventData &att
         the_new_any = &(attr_value.attr_val->value);
     }
 
-//
-// get the mutex to synchronize the sending of events
-//
-
-    omni_mutex_lock l(detect_mutex);
-
 //
 // Send event, if the read_attribute failed or if it is the first time that the read_attribute succeed after a failure.
 // Same thing if the attribute quality factor changes to INVALID

cppapi/server/eventsupplier.h

@@ -174,9 +174,7 @@ protected :
 	static omni_mutex 		push_mutex;
 	static omni_condition	push_cond;
 
-	// Added a mutex to synchronize the access to
-	//	detect_event which is used
-	// from different threads
+	// Unused, replaced with event_mutex. Left for backward compatibility.
 	static omni_mutex		detect_mutex;
 
 private: