PS-3951: Fix decreasing status counters

Status counters were cleaned in THD::release_resources, before an optional thread cleanup.
The cleanup could possibly perform a rollback, or other counter-increasing operations.
In this case, these additions to the thread local counters were lost during the destruction of the thread, but were visible for a short time, before the thread was removed from the global thread list.

This change avoids this issue by moving the global counter update to the end of the release_resources method, ensuring that possible counter-changing operation happen before it.

mysql-test/r/bug90351.result

@@ -0,0 +1,6 @@
+CREATE TABLE t1 (i INTEGER);
+INSERT INTO t1 VALUES (1);
+SET AUTOCOMMIT=0;
+START TRANSACTION;
+DELETE FROM t1;
+DROP TABLE t1;

mysql-test/t/bug90351.test

@@ -0,0 +1,26 @@
+#
+# Bug 90351: status counters decrease on thread destruction
+#
+--source include/have_innodb.inc
+--source include/count_sessions.inc
+
+connect (con1,localhost,root,,);
+
+connection con1;
+CREATE TABLE t1 (i INTEGER);
+INSERT INTO t1 VALUES (1);
+let $con1_id= `SELECT connection_id()`;
+SET AUTOCOMMIT=0;
+START TRANSACTION;
+DELETE FROM t1;
+
+connection default;
+--disable_query_log
+eval KILL $con1_id;
+--enable_query_log
+
+connection default;
+DROP TABLE t1;
+
+disconnect con1;
+--source include/wait_until_count_sessions.inc

sql/sql_class.cc

@@ -1773,11 +1773,6 @@ void THD::release_resources()
   mysql_mutex_assert_not_owner(&LOCK_thread_count);
   DBUG_ASSERT(m_release_resources_done == false);
 
-  mysql_mutex_lock(&LOCK_status);
-  add_to_status(&global_status_var, &status_var);
-  memset(&status_var, 0, sizeof(status_var));
-  mysql_mutex_unlock(&LOCK_status);
-
   /* Ensure that no one is using THD */
   mysql_mutex_lock(&LOCK_thd_data);
 
@@ -1802,6 +1797,10 @@ void THD::release_resources()
   if (m_enable_plugins)
     plugin_thdvar_cleanup(this);
 
+  mysql_mutex_lock(&LOCK_status);
+  add_to_status(&global_status_var, &status_var);
+  mysql_mutex_unlock(&LOCK_status);
+  memset(&status_var, 0, sizeof(status_var));
   m_release_resources_done= true;
 }
 
@@ -1816,6 +1815,14 @@ THD::~THD()
   if (!m_release_resources_done)
     release_resources();
 
+#ifndef DBUG_OFF
+  {
+    const char* empty_status[sizeof(status_var)] = {};
+    DBUG_ASSERT(memcmp(reinterpret_cast<void*>(&status_var),
+                empty_status, sizeof(status_var))==0);
+  }
+#endif // DBUG_OFF
+
   clear_next_event_pos();
 
   /* Ensure that no one is using THD */