MDEV-17167 - InnoDB: Failing assertion: table->get_ref_count() == 0 upon

             truncating a temporary table

TRUNCATE expects only one TABLE instance (which is used by TRUNCATE
itself) to be open. However this requirement wasn't enforced after
"MDEV-5535: Cannot reopen temporary table".

Fixed by closing unused table instances before performing TRUNCATE.

mysql-test/main/temp_table.result

@@ -548,3 +548,27 @@ DROP TABLE nonexisting_table, t1;
 ERROR 42S02: Unknown table 'temp_db.nonexisting_table'
 # Cleanup
 DROP DATABASE temp_db;
+USE test;
+#
+# MDEV-17167 - InnoDB: Failing assertion: table->get_ref_count() == 0
+#              upon truncating a temporary table
+#
+CREATE TEMPORARY TABLE t1(a INT) ENGINE=InnoDB;
+SELECT * FROM t1 AS t1a1, t1 AS t2a2;
+a	a
+TRUNCATE TABLE t1;
+LOCK TABLES t1 WRITE;
+TRUNCATE TABLE t1;
+SELECT * FROM t1;
+a
+UNLOCK TABLES;
+LOCK TABLES t1 AS t1a1 WRITE, t1 AS t1a2 WRITE;
+TRUNCATE TABLE t1;
+SELECT * FROM t1 AS t1a1, t1 AS t1a2;
+a	a
+UNLOCK TABLES;
+CREATE TABLE t2(a INT) ENGINE=InnoDB;
+LOCK TABLES t2 WRITE;
+TRUNCATE TABLE t1;
+UNLOCK TABLES;
+DROP TABLE t1, t2;

mysql-test/main/temp_table.test

@@ -594,4 +594,30 @@ DROP TABLE nonexisting_table, t1;
 
 --echo # Cleanup
 DROP DATABASE temp_db;
+USE test;
 
+
+--echo #
+--echo # MDEV-17167 - InnoDB: Failing assertion: table->get_ref_count() == 0
+--echo #              upon truncating a temporary table
+--echo #
+CREATE TEMPORARY TABLE t1(a INT) ENGINE=InnoDB;
+SELECT * FROM t1 AS t1a1, t1 AS t2a2;
+TRUNCATE TABLE t1;
+
+LOCK TABLES t1 WRITE;
+TRUNCATE TABLE t1;
+SELECT * FROM t1;
+UNLOCK TABLES;
+
+LOCK TABLES t1 AS t1a1 WRITE, t1 AS t1a2 WRITE;
+TRUNCATE TABLE t1;
+SELECT * FROM t1 AS t1a1, t1 AS t1a2;
+UNLOCK TABLES;
+
+CREATE TABLE t2(a INT) ENGINE=InnoDB;
+LOCK TABLES t2 WRITE;
+TRUNCATE TABLE t1;
+UNLOCK TABLES;
+
+DROP TABLE t1, t2;

sql/sql_class.h

@@ -4628,6 +4628,7 @@ class THD :public Statement,
 
   TMP_TABLE_SHARE* save_tmp_table_share(TABLE *table);
   void restore_tmp_table_share(TMP_TABLE_SHARE *share);
+  void close_unused_temporary_table_instances(const TABLE_LIST *tl);
 
 private:
   /* Whether a lock has been acquired? */

sql/sql_plist.h

@@ -184,7 +184,12 @@ class I_P_List_iterator
     list= &a;
     current= a.m_first;
   }
-  /* Operator for it++ */
+  /**
+    Operator for it++
+
+    @note since we save next element pointer, caller may remove current element.
+    Such modification doesn't invalidate iterator.
+  */
   inline T* operator++(int)
   {
     T *result= current;

sql/sql_truncate.cc

@@ -401,6 +401,8 @@ bool Sql_cmd_truncate_table::truncate_table(THD *thd, TABLE_LIST *table_ref)
     /* In RBR, the statement is not binlogged if the table is temporary. */
     binlog_stmt= !thd->is_current_stmt_binlog_format_row();
 
+    thd->close_unused_temporary_table_instances(table_ref);
+
     error= handler_truncate(thd, table_ref, TRUE);
 
     /*

sql/temporary_tables.cc

@@ -1540,3 +1540,33 @@ void THD::unlock_temporary_tables()
   DBUG_VOID_RETURN;
 }
 
+
+/**
+  Close unused TABLE instances for given temporary table.
+
+  @param tl [IN]                      TABLE_LIST
+
+  Initial use case was TRUNCATE, which expects only one instance (which is used
+  by TRUNCATE itself) to be open. Most probably some ALTER TABLE variants and
+  REPAIR may have similar expectations.
+*/
+
+void THD::close_unused_temporary_table_instances(const TABLE_LIST *tl)
+{
+  TMP_TABLE_SHARE *share= find_tmp_table_share(tl);
+
+  if (share)
+  {
+    All_share_tables_list::Iterator tables_it(share->all_tmp_tables);
+
+     while (TABLE *table= tables_it++)
+     {
+       if (table->query_id == 0)
+       {
+         /* Note: removing current list element doesn't invalidate iterator. */
+         share->all_tmp_tables.remove(table);
+         free_temporary_table(table);
+       }
+     }
+  }
+}