server GetField ensure no duplicate reply

src/server/pv/responseHandlers.h

@@ -687,6 +687,7 @@ public:
     void destroy();
     void send(epics::pvData::ByteBuffer* buffer, TransportSendControl* control);
 private:
+    bool done;
     epics::pvData::Status _status;
     epics::pvData::FieldConstPtr _field;
 };

src/server/pv/serverChannelImpl.h

@@ -48,7 +48,7 @@ public:
     void unregisterRequest(pvAccessID id);
 
     void installGetField(const GetFieldRequester::shared_pointer& gf);
-    void completeGetField();
+    void completeGetField(GetFieldRequester *req);
 
     //! may return NULL
     Destroyable::shared_pointer getRequest(pvAccessID id);

src/server/responseHandlers.cpp

@@ -2783,20 +2783,25 @@ void ServerGetFieldHandler::getFieldFailureResponse(Transport::shared_pointer co
 ServerGetFieldRequesterImpl::ServerGetFieldRequesterImpl(
     ServerContextImpl::shared_pointer const & context, ServerChannel::shared_pointer const & channel,
     const pvAccessID ioid, Transport::shared_pointer const & transport) :
-    BaseChannelRequester(context, channel, ioid, transport), _field()
+    BaseChannelRequester(context, channel, ioid, transport), done(false)
 {
 }
 
 void ServerGetFieldRequesterImpl::getDone(const Status& status, FieldConstPtr const & field)
 {
+    bool twice;
     {
         Lock guard(_mutex);
         _status = status;
         _field = field;
+        twice = done;
+        done = true;
     }
-    TransportSender::shared_pointer thisSender = shared_from_this();
-    _transport->enqueueSendRequest(thisSender);
-    _channel->completeGetField();
+    if(!twice) {
+        TransportSender::shared_pointer thisSender = shared_from_this();
+        _transport->enqueueSendRequest(thisSender);
+    }
+    _channel->completeGetField(this);
 }
 
 void ServerGetFieldRequesterImpl::destroy()

src/server/serverChannelImpl.cpp

@@ -121,12 +121,13 @@ void ServerChannel::installGetField(const GetFieldRequester::shared_pointer& gf)
     }
 }
 
-void ServerChannel::completeGetField()
+void ServerChannel::completeGetField(GetFieldRequester *req)
 {
     GetFieldRequester::shared_pointer prev;
     {
         epicsGuard<epicsMutex> G(_mutex);
-        prev.swap(_active_requester);
+        if(_active_requester.get()==req)
+            prev.swap(_active_requester);
     }
 }