MDEV-4956 - Reduce usage of LOCK_open: TABLE_SHARE::tdc.used_tables

- tc_acquire_table and tc_release_table do not access
  TABLE_SHARE::tdc.used_tables anymore
- in tc_acquire_table(): release LOCK_tdc after we relase LOCK_open
  (saves a few CPU cycles in critical section)
- in tc_release_table(): if we reached table cache threshold, evict
  to-be-released table without moving it to unused_tables. unused_tables
  must be empty at this point.

1 files changed, 15 insertions, 13 deletions

diff --git a/sql/sql_test.cc b/sql/sql_test.cc
index 1a241521fd7..151ceed4006 100644
--- a/sql/sql_test.cc
+++ b/sql/sql_test.cc
@@ -92,21 +92,23 @@ static void print_cached_tables(void)
   mysql_mutex_lock(&LOCK_open);
   while ((share= tdc_it.next()))
   {
-    TABLE_SHARE::TABLE_list::Iterator it(share->tdc.used_tables);
+    TABLE_SHARE::All_share_tables_list::Iterator it(share->tdc.all_tables);
     while ((entry= it++))
     {
-      printf("%-14.14s %-32s%6ld%8ld%6d  %s\n",
-             entry->s->db.str, entry->s->table_name.str, entry->s->version,
-             entry->in_use->thread_id, entry->db_stat ? 1 : 0,
-             lock_descriptions[(int)entry->reginfo.lock_type]);
-    }
-    it.init(share->tdc.free_tables);
-    while ((entry= it++))
-    {
-      unused++;
-      printf("%-14.14s %-32s%6ld%8ld%6d  %s\n",
-             entry->s->db.str, entry->s->table_name.str, entry->s->version,
-             0L, entry->db_stat ? 1 : 0, "Not in use");
+      if (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->thread_id, entry->db_stat ? 1 : 0,
+               lock_descriptions[(int)entry->reginfo.lock_type]);
+      }
+      else
+      {
+        unused++;
+        printf("%-14.14s %-32s%6ld%8ld%6d  %s\n",
+               entry->s->db.str, entry->s->table_name.str, entry->s->version,
+               0L, entry->db_stat ? 1 : 0, "Not in use");
+      }
     }
   }
   tdc_it.deinit();