Optimize flush tables with read lock (FTWRL) to not wait for select's

Part of MDEV-5336 Implement LOCK FOR BACKUP

The idea is that instead of waiting in close_cached_tables() for all
tables to be closed, we instead call flush_tables() that does:
- Flush not used objects in table cache to free memory
- Collect all tables that are open
- Call HA_EXTRA_FLUSH on the objects, to get them into "closed state"
- Added HA_EXTRA_FLUSH support to archive and CSV
- Added multi-user protection to HA_EXTRA_FLUSH in MyISAM and Aria

The benefit compared to old code is:
- FTWRL doesn't have to wait for long running read operations or
  open HANDLER's

1 files changed, 15 insertions, 1 deletions

diff --git a/mysql-test/main/mdl_sync.result b/mysql-test/main/mdl_sync.result
index 3880fc5ef91..bf659a3616f 100644
--- a/mysql-test/main/mdl_sync.result
+++ b/mysql-test/main/mdl_sync.result
@@ -3055,7 +3055,7 @@ disconnect con3;
 #
 CREATE TABLE t1(a INT) ENGINE=InnoDB;
 SET debug_sync='open_tables_after_open_and_process_table SIGNAL ready WAIT_FOR go';
-SELECT * FROM t1;
+INSERT INTO t1 values (1);
 connect  con1,localhost,root,,;
 SET debug_sync='now WAIT_FOR ready';
 SET lock_wait_timeout=1;
@@ -3063,7 +3063,21 @@ FLUSH TABLES WITH READ LOCK;
 ERROR HY000: Lock wait timeout exceeded; try restarting transaction
 SET debug_sync='now SIGNAL go';
 connection default;
+# After MDEV-5536, SELECT will not block FLUSH TABLES
+SET debug_sync='RESET';
+SET debug_sync='open_tables_after_open_and_process_table SIGNAL ready WAIT_FOR go';
+SELECT * FROM t1;
+connection con1;
+SET debug_sync='now WAIT_FOR ready';
+SET lock_wait_timeout=1;
+FLUSH TABLES WITH READ LOCK;
+SET debug_sync='now SIGNAL go';
+connection default;
 a
+1
+connection con1;
+unlock tables;
+connection default;
 SET debug_sync='RESET';
 DROP TABLE t1;
 disconnect con1;