Fix for MDEV-8301; Statistics for a thread could be counted twice in SHOW...

Fix for MDEV-8301;  Statistics for a thread could be counted twice in SHOW STATUS while thread was ending

Fixed by adding a marker if we have added the thread statistics to the global counters.

sql/sql_class.cc

@@ -1263,6 +1263,7 @@ void THD::init(void)
   bzero((char *) &status_var, sizeof(status_var));
   bzero((char *) &org_status_var, sizeof(org_status_var));
   start_bytes_received= 0;
+  status_in_global= 0;
 
   if (variables.sql_log_bin)
     variables.option_bits|= OPTION_BIN_LOG;
@@ -1366,6 +1367,7 @@ void THD::change_user(void)
   cleanup();
   reset_killed();
   cleanup_done= 0;
+  status_in_global= 0;
   init();
   stmt_map.reset();
   my_hash_init(&user_vars, system_charset_info, USER_VARS_HASH_SIZE, 0, 0,

sql/sql_class.h

@@ -1733,11 +1733,11 @@ public:
   /* Do not set socket timeouts for wait_timeout (used with threadpool) */
   bool skip_wait_timeout;
 
-  /* container for handler's private per-connection data */
-  Ha_data ha_data[MAX_HA];
-
   bool prepare_derived_at_open;
 
+  /* Set to 1 if status of this THD is already in global status */
+  bool status_in_global;
+
   /* 
     To signal that the tmp table to be created is created for materialized
     derived table or a view.
@@ -1746,6 +1746,9 @@ public:
 
   bool save_prep_leaf_list;
 
+  /* container for handler's private per-connection data */
+  Ha_data ha_data[MAX_HA];
+
 #ifndef MYSQL_CLIENT
   binlog_cache_mngr *  binlog_setup_trx_data();
 
@@ -3116,6 +3119,8 @@ public:
   {
     mysql_mutex_lock(&LOCK_status);
     add_to_status(&global_status_var, &status_var);
+    /* Mark that this THD status has already been added in global status */
+    status_in_global= 1;
     mysql_mutex_unlock(&LOCK_status);
   }
 

sql/sql_show.cc

@@ -3109,7 +3109,10 @@ void calc_sum_of_all_status(STATUS_VAR *to)
 
   /* Add to this status from existing threads */
   while ((tmp= it++))
+  {
+    if (!tmp->status_in_global)
       add_to_status(to, &tmp->status_var);
+  }
   
   mysql_mutex_unlock(&LOCK_thread_count);
   DBUG_VOID_RETURN;