restart runMainThread in cluster discovery

src/Interpreters/ClusterDiscovery.cpp

@@ -322,19 +322,29 @@ void ClusterDiscovery::start()
     }
 
     main_thread = ThreadFromGlobalPool([this]
+    {
+        bool finish = false;
+        while (!finish)
         {
             try
             {
-            runMainThread();
+                finish = runMainThread();
             }
             catch (...)
             {
+                /*
+                 * it can be zk error (will take new session) or other retriable error,
+                 * should not stop discovery forever
+                 */
                 tryLogCurrentException(log, "Caught exception in cluster discovery runMainThread");
             }
+        }
     });
 }
 
-void ClusterDiscovery::runMainThread()
+
+/// Returns `true` on gracefull shutdown (no restart required)
+bool ClusterDiscovery::runMainThread()
 {
     setThreadName("ClusterDiscover");
     LOG_DEBUG(log, "Worker thread started");
@@ -362,6 +372,7 @@ void ClusterDiscovery::runMainThread()
         }
     }
     LOG_DEBUG(log, "Worker thread stopped");
+    return stop_flag;
 }
 
 void ClusterDiscovery::shutdown()

src/Interpreters/ClusterDiscovery.h

@@ -94,7 +94,7 @@ private:
     bool updateCluster(const String & cluster_name);
     bool updateCluster(ClusterInfo & cluster_info);
 
-    void runMainThread();
+    bool runMainThread();
     void shutdown();
 
     /// cluster name -> cluster info (zk root, set of nodes)