Bug #45225 Locking: hang if drop table with no timeout

This patch introduces timeouts for metadata locks. 

The timeout is specified in seconds using the new dynamic system 
variable  "lock_wait_timeout" which has both GLOBAL and SESSION
scopes. Allowed values range from 1 to 31536000 seconds (= 1 year). 
The default value is 1 year.

The new server parameter "lock-wait-timeout" can be used to set
the default value parameter upon server startup.

"lock_wait_timeout" applies to all statements that use metadata locks.
These include DML and DDL operations on tables, views, stored procedures
and stored functions. They also include LOCK TABLES, FLUSH TABLES WITH
READ LOCK and HANDLER statements.

The patch also changes thr_lock.c code (table data locks used by MyISAM
and other simplistic engines) to use the same system variable.
InnoDB row locks are unaffected.

One exception to the handling of the "lock_wait_timeout" variable
is delayed inserts. All delayed inserts are executed with a timeout
of 1 year regardless of the setting for the global variable. As the
connection issuing the delayed insert gets no notification of 
delayed insert timeouts, we want to avoid unnecessary timeouts.

It's important to note that the timeout value is used for each lock
acquired and that one statement can take more than one lock.
A statement can therefore block for longer than the lock_wait_timeout 
value before reporting a timeout error. When lock timeout occurs, 
ER_LOCK_WAIT_TIMEOUT is reported.

Test case added to lock_multi.test.


include/my_pthread.h:
  Added macros for comparing two timespec structs.
include/thr_lock.h:
  Introduced timeouts for thr_lock.c locks.
mysql-test/r/mysqld--help-notwin.result:
  Updated result file with the new server variable.
mysql-test/r/mysqld--help-win.result:
  Updated result file with the new server variable.
mysql-test/suite/sys_vars/r/lock_wait_timeout_basic.result:
  Added basic test for the new server variable.
mysql-test/suite/sys_vars/t/lock_wait_timeout_basic.test:
  Added basic test for the new server variable.
mysys/thr_lock.c:
  Introduced timeouts for thr_lock.c locks.
sql/mdl.cc:
  Introduced timeouts for metadata locks.
sql/mdl.h:
  Introduced timeouts for metadata locks.
sql/sql_base.cc:
  Introduced timeouts in tdc_wait_for_old_versions().
sql/sql_class.h:
  Added new server variable lock_wait_timeout.
sql/sys_vars.cc:
  Added new server variable lock_wait_timeout.

1 files changed, 161 insertions, 0 deletions

diff --git a/mysql-test/t/lock_multi.test b/mysql-test/t/lock_multi.test
index 5b64f60b6eb..1080b44c448 100644
--- a/mysql-test/t/lock_multi.test
+++ b/mysql-test/t/lock_multi.test
@@ -877,5 +877,166 @@ drop view v1;
 drop table t1;
 
 
+--echo #
+--echo # Bug#45225 Locking: hang if drop table with no timeout
+--echo #
+--echo # These tests also provide function coverage for the
+--echo # lock_wait_timeout server variable.
+--echo #
+
+--disable_warnings
+DROP TABLE IF EXISTS t1;
+--enable_warnings
+
+CREATE TABLE t1 (id int);
+
+connect(con2, localhost, root,,);
+SET SESSION lock_wait_timeout= 1;
+
+--echo #
+--echo # Test 1: acquire exclusive lock
+--echo #
+
+--echo # Connection default
+connection default;
+START TRANSACTION;
+INSERT INTO t1 VALUES (1);
+
+--echo # Connection 2
+connection con2;
+--error ER_LOCK_WAIT_TIMEOUT
+DROP TABLE t1;
+
+--echo # Connection default
+connection default;
+COMMIT;
+
+--echo #
+--echo # Test 2: upgrade shared lock
+--echo #
+
+--echo # Connection default
+connection default;
+START TRANSACTION;
+SELECT * FROM t1;
+
+--echo # Connection 2
+connection con2;
+--error ER_LOCK_WAIT_TIMEOUT
+ALTER TABLE t1 RENAME TO t2;
+
+--echo # Connection default
+connection default;
+COMMIT;
+
+--echo #
+--echo # Test 3: acquire shared lock
+--echo #
+
+--echo # Connection default
+connection default;
+LOCK TABLE t1 WRITE;
+
+--echo # Connection 2
+connection con2;
+--error ER_LOCK_WAIT_TIMEOUT
+INSERT INTO t1(id) VALUES (2);
+
+--echo # Connection default
+connection default;
+UNLOCK TABLES;
+
+--echo #
+--echo # Test 4: table level locks
+--echo #
+
+--echo # Connection default
+connection default;
+LOCK TABLE t1 READ;
+
+--echo # Connection 2
+connection con2;
+--error ER_LOCK_WAIT_TIMEOUT
+INSERT INTO t1(id) VALUES(4);
+
+--echo # Connection default
+connection default;
+UNLOCK TABLES;
+
+--echo #
+--echo # Test 5: Waiting on Table Definition Cache (TDC)
+--echo #
+
+connect(con3, localhost, root);
+
+--echo # Connection default
+connection default;
+LOCK TABLE t1 READ;
+
+--echo # Connection con3
+connection con3;
+--echo # Sending:
+--send FLUSH TABLES
+
+--echo # Connection con2
+connection con2;
+let $wait_condition=
+  SELECT COUNT(*) = 1 FROM information_schema.processlist
+  WHERE state = "Flushing tables" AND info = "FLUSH TABLES";
+--source include/wait_condition.inc
+--error ER_LOCK_WAIT_TIMEOUT
+SELECT * FROM t1;
+
+--echo # Connection default
+connection default;
+UNLOCK TABLES;
+
+--echo # Connection con3
+connection con3;
+--echo # Reaping: FLUSH TABLES
+--reap
+
+--echo #
+--echo # Test 6: Timeouts in I_S queries
+--echo #
+
+--echo # Connection default
+connection default;
+CREATE TABLE t2 (id INT);
+LOCK TABLE t2 WRITE;
+
+--echo # Connection con3
+connection con3;
+--echo # Sending:
+--send DROP TABLE t1, t2
+
+--echo # Connection con2
+connection con2;
+let $wait_condition=
+  SELECT COUNT(*) = 1 FROM information_schema.processlist
+  WHERE state = "Waiting for table" AND info = "DROP TABLE t1, t2";
+--source include/wait_condition.inc
+# Note: This query causes two timeouts.
+# 1: try_acquire_high_prio_shared_mdl_lock on t1
+# 2: recover_from_failed_open on t1
+SELECT table_name, table_comment FROM information_schema.tables
+  WHERE table_schema= 'test' AND table_name= 't1';
+
+--echo # Connection default
+connection default;
+UNLOCK TABLES;
+
+--echo # Connection con3
+connection con3;
+--echo # Reaping: DROP TABLE t1, t2
+--reap
+
+--echo # Connection default
+connection default;
+--echo # Cleanup
+disconnect con2;
+disconnect con3;
+
+
 # Wait till all disconnects are completed
 --source include/wait_until_count_sessions.inc