MDEV-5492 - Reduce usage of LOCK_open: TABLE::in_use

Move TABLE::in_use out of LOCK_open.

This is done with assumtion that foreign threads accessing TABLE::in_use
will only need consistent value _after_ marking table for flush and purging
unused table instances. In this case TABLE::in_use will always point to a
valid thread object.

Previously FLUSH TABLES thread may wait for tables flushed subsequently by
concurrent threads which breaks the above assumption, e.g.:
open tables: t1 (version= 1)
thr1 (FLUSH TABLES): refresh_version++
thr1 (FLUSH TABLES): purge table cache
open tables: none
thr2 (SELECT * FROM t1): open tables: t1
open tables: t1 (version= 2)
thr2 (FLUSH TABLES): refresh_version++
thr2 (FLUSH TABLES): purge table cache
thr1 (FLUSH TABLES): wait for old tables (including t1 with version 2)

It is fixed so that FLUSH TABLES waits only for tables that were open
heretofore.

1 files changed, 5 insertions, 4 deletions

diff --git a/sql/sql_test.cc b/sql/sql_test.cc
index 922423bef26..8588d6564ca 100644
--- a/sql/sql_test.cc
+++ b/sql/sql_test.cc
@@ -94,12 +94,13 @@ static void print_cached_tables(void)
     TABLE_SHARE::All_share_tables_list::Iterator it(share->tdc.all_tables);
     while ((entry= it++))
     {
+      THD *in_use= entry->in_use;
       printf("%-14.14s %-32s%6ld%8ld%6d  %s\n",
-             entry->s->db.str, entry->s->table_name.str, entry->s->version,
-             entry->in_use ? entry->in_use->thread_id : 0,
+             entry->s->db.str, entry->s->table_name.str, entry->s->tdc.version,
+             in_use ? in_use->thread_id : 0,
              entry->db_stat ? 1 : 0,
-             entry->in_use ? lock_descriptions[(int)entry->reginfo.lock_type] :
-                             "Not in use");
+             in_use ? lock_descriptions[(int)entry->reginfo.lock_type] :
+                      "Not in use");
     }
   }
   mysql_mutex_unlock(&LOCK_open);