main.mdev-504 unveils assertion failure in TABLE_SHARE::visit_subgraph

CREATE TABLE t1(a INT);

SELECT * FROM t1;

SET debug_sync='tc_acquire_table SIGNAL ready WAIT_FOR go';

--send SELECT * FROM t1

connect(con1, localhost, root,, test);

SET debug_sync='now WAIT_FOR ready';

FLUSH TABLE t1;

SET debug_sync='now SIGNAL go';

connection default;

reap;

disconnect con1;

DROP TABLE t1;

=== modified file 'sql/table_cache.cc'

--- sql/table_cache.cc	2014-03-20 07:11:13 +0000

+++ sql/table_cache.cc	2014-03-27 15:02:31 +0000

@@ -334,6 +334,8 @@ static TABLE *tc_acquire_table(THD *thd,

   table= share->tdc.free_tables.pop_front();

   mysql_mutex_unlock(&share->tdc.LOCK_table_share);

+  DEBUG_SYNC(thd, "tc_acquire_table");

+

   if (table)

   {

     DBUG_ASSERT(!table->in_use);