block using QC in case of having tables locked by LOCK... (BUG#12385)

mysql-test/r/query_cache_noembeded.result

+set GLOBAL query_cache_size=1355776;
+reset query cache;
+flush status;
+CREATE TABLE t1 ( a INT NOT NULL PRIMARY KEY AUTO_INCREMENT ) ENGINE =
+MyISAM;
+LOCK TABLE t1 READ LOCAL;
+INSERT INTO t1 VALUES (), (), ();
+SELECT * FROM t1;
+a
+SELECT * FROM t1;
+a
+1
+2
+3
+SELECT * FROM t1;
+a
+drop table t1;
+set GLOBAL query_cache_size=default;

mysql-test/t/query_cache_noembeded.test

+-- source include/have_query_cache.inc
+-- source include/not_embedded.inc
+
+#
+# Tests with query cache
+#
+set GLOBAL query_cache_size=1355776;
+
+# Reset query cache variables.
+
+reset query cache;
+flush status;
+
+#
+# do not use QC if tables locked (BUG#12385)
+#
+connect (root,localhost,root,,test,$MASTER_MYPORT,master.sock);
+connection root;
+CREATE TABLE t1 ( a INT NOT NULL PRIMARY KEY AUTO_INCREMENT ) ENGINE =
+MyISAM;
+LOCK TABLE t1 READ LOCAL;
+connect (root2,localhost,root,,test,$MASTER_MYPORT,master.sock);
+connection root2;
+INSERT INTO t1 VALUES (), (), ();
+connection root;
+SELECT * FROM t1;
+connection root2;
+SELECT * FROM t1;
+connection root;
+SELECT * FROM t1;
+drop table t1;
+
+set GLOBAL query_cache_size=default;

sql/sql_cache.cc

@@ -739,7 +739,7 @@ void Query_cache::store_query(THD *thd, TABLE_LIST *tables_used)
   TABLE_COUNTER_TYPE local_tables;
   ulong tot_length;
   DBUG_ENTER("Query_cache::store_query");
-  if (query_cache_size == 0)
+  if (query_cache_size == 0 || thd->locked_tables)
     DBUG_VOID_RETURN;
 
   if ((local_tables= is_cacheable(thd, thd->query_length,
@@ -750,7 +750,10 @@ void Query_cache::store_query(THD *thd, TABLE_LIST *tables_used)
     STRUCT_LOCK(&structure_guard_mutex);
 
     if (query_cache_size == 0)
+    {
+      STRUCT_UNLOCK(&structure_guard_mutex);
       DBUG_VOID_RETURN;
+    }
     DUMP(this);
 
     /* Key is query + database + flag */
@@ -874,7 +877,7 @@ Query_cache::send_result_to_client(THD *thd, char *sql, uint query_length)
   byte flags;
   DBUG_ENTER("Query_cache::send_result_to_client");
 
-  if (query_cache_size == 0 ||
+  if (query_cache_size == 0 || thd->locked_tables ||
       /*
 	it is not possible to check has_transactions() function of handler
 	because tables not opened yet