show variables exception

Author: yanhuqing666

src/main/java/com/actiontech/dble/DbleServer.java

@@ -271,7 +271,12 @@ private void pullVarAndMeta() throws IOException {
         if (!this.getConfig().isDataHostWithoutWR()) {
             //init for sys VAR
             VarsExtractorHandler handler = new VarsExtractorHandler(config.getDataHosts());
-            systemVariables = handler.execute();
+            SystemVariables newSystemVariables = handler.execute();
+            if (newSystemVariables == null) {
+                throw new IOException("Can't get variables from data node");
+            } else {
+                systemVariables = newSystemVariables;
+            }
             reviseSchemas();
             initDataHost();
             //init tmManager

src/main/java/com/actiontech/dble/manager/response/ReloadConfig.java

@@ -43,6 +43,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.List;
@@ -274,10 +275,13 @@ public static void reloadAll(final int loadAllMode) throws Exception {
         Map<ERTable, Set<ERTable>> newErRelations = loader.getErRelations();
         FirewallConfig newFirewall = loader.getFirewall();
 
-        SystemVariables newSystemVariables = DbleServer.getInstance().getSystemVariables();
+        SystemVariables newSystemVariables = null;
         if (!loader.isDataHostWithoutWH()) {
             VarsExtractorHandler handler = new VarsExtractorHandler(newDataHosts);
             newSystemVariables = handler.execute();
+            if (newSystemVariables == null) {
+                throw new IOException("Can't get variables from data node");
+            }
             ConfigInitializer confInit = new ConfigInitializer(newSystemVariables.isLowerCaseTableNames());
             newUsers = confInit.getUsers();
             newSchemas = confInit.getSchemas();

src/main/java/com/actiontech/dble/server/variables/VarsExtractorHandler.java

@@ -27,7 +27,7 @@ public class VarsExtractorHandler {
     private Lock lock;
     private Condition done;
     private Map<String, PhysicalDBPool> dataHosts;
-    private SystemVariables systemVariables = new SystemVariables();
+    private volatile SystemVariables systemVariables = null;
     public VarsExtractorHandler(Map<String, PhysicalDBPool> dataHosts) {
         this.dataHosts = dataHosts;
         this.extracting = false;
@@ -77,7 +77,8 @@ private PhysicalDatasource getPhysicalDatasource() {
         return ds;
     }
 
-    public void handleVars(Map<String, String> vars) {
+    void handleVars(Map<String, String> vars) {
+        systemVariables = new SystemVariables();
         for (Map.Entry<String, String> entry : vars.entrySet()) {
             String key = entry.getKey();
             String value = entry.getValue();