Perf improvement on Monitor read_only_check

if possible, try to call mysql_query_start() as early as possible

lib/MySQL_Monitor.cpp

@@ -546,25 +546,25 @@ void * monitor_read_only_thread(void *arg) {
 	if (!GloMTH) return NULL;	// quick exit during shutdown/restart
 
 	mmsd->mysql=GloMyMon->My_Conn_Pool->get_connection(mmsd->hostname, mmsd->port);
-	unsigned long long start_time=mysql_thr->curtime;
-
-
-	mmsd->t1=start_time;
 
+	unsigned long long start_time=mysql_thr->curtime;
 	bool crc=false;
-	if (mmsd->mysql==NULL) { // we don't have a connection, let's create it
-		bool rc;
-		rc=mmsd->create_new_connection();
-		crc=true;
-		if (rc==false) {
-			goto __exit_monitor_read_only_thread;
+	if (mmsd->mysql==NULL) {
+		mmsd->mysql=GloMyMon->My_Conn_Pool->get_connection(mmsd->hostname, mmsd->port);
+
+		mmsd->t1=start_time;
+		if (mmsd->mysql==NULL) { // we don't have a connection, let's create it
+			bool rc;
+			rc=mmsd->create_new_connection();
+			crc=true;
+			if (rc==false) {
+				goto __exit_monitor_read_only_thread;
+			}
 		}
+		mmsd->t1=monotonic_time();
+		mmsd->async_exit_status=mysql_query_start(&mmsd->interr,mmsd->mysql,"SHOW GLOBAL VARIABLES LIKE 'read_only'");
 	}
-
-	mmsd->t1=monotonic_time();
-	//async_exit_status=mysql_change_user_start(&ret_bool, mysql,"msandbox2","msandbox2","information_schema");
-	//mmsd->async_exit_status=mysql_ping_start(&mmsd->interr,mmsd->mysql);
-	mmsd->async_exit_status=mysql_query_start(&mmsd->interr,mmsd->mysql,"SHOW GLOBAL VARIABLES LIKE 'read_only'");
+  start_time=mmsd->t1;
 	while (mmsd->async_exit_status) {
 		mmsd->async_exit_status=wait_for_mysql(mmsd->mysql, mmsd->async_exit_status);
 		unsigned long long now=monotonic_time();
@@ -1223,6 +1223,13 @@ void * MySQL_Monitor::monitor_read_only() {
 				//	perror("Thread creation monitor_read_only_thread");
 				//}
 				WorkItem* item;
+				{ // try to initialize it here
+					mmsd->mysql=GloMyMon->My_Conn_Pool->get_connection(mmsd->hostname, mmsd->port);
+					if (mmsd->mysql) {
+						mmsd->t1=monotonic_time();
+						mmsd->async_exit_status=mysql_query_start(&mmsd->interr,mmsd->mysql,"SHOW GLOBAL VARIABLES LIKE 'read_only'");
+					}
+				}
 				item=new WorkItem(mmsd,monitor_read_only_thread);
 				GloMyMon->queue.add(item);
 			}