[inner-1762] fix：no handler (cherry pick)

src/main/java/com/actiontech/dble/services/mysqlsharding/MySQLResponseService.java

@@ -50,7 +50,7 @@ import java.util.concurrent.locks.LockSupport;
 public class MySQLResponseService extends VariablesService {
     private static final Logger LOGGER = LoggerFactory.getLogger(MySQLResponseService.class);
 
-    private ResponseHandler responseHandler;
+    private volatile ResponseHandler responseHandler;
 
     protected final AtomicBoolean isHandling = new AtomicBoolean(false);
 
@@ -458,7 +458,7 @@ public class MySQLResponseService extends VariablesService {
         for (Map.Entry<String, String> entry : tmpSysVars.entrySet()) {
             String value = DbleServer.getInstance().getSystemVariables().getDefaultValue(entry.getKey());
             try {
-                BigDecimal vl = new BigDecimal(value);
+                new BigDecimal(value);
             } catch (NumberFormatException e) {
                 value = "`" + value + "`";
             }

src/main/java/com/actiontech/dble/services/mysqlsharding/MysqlBackendLogicHandler.java

@@ -156,12 +156,11 @@ public class MysqlBackendLogicHandler {
         if (service.getSession() != null && !service.isTesting() && service.getLogResponse().compareAndSet(false, true)) {
             service.getSession().setBackendResponseEndTime(this.service);
         }
-        service.setExecuting(false);
-        service.setRowDataFlowing(false);
         service.getLogResponse().set(false);
-        service.signal();
-        if (service.getResponseHandler() != null) {
-            service.getResponseHandler().rowEofResponse(data, false, service);
+        ResponseHandler respHand = service.getResponseHandler();
+        if (respHand != null) {
+            service.backendSpecialCleanUp();
+            respHand.rowEofResponse(data, false, service);
         } else {
             closeNoHandler();
         }