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, 7 insertions, 7 deletions

diff --git a/sql/mdl.h b/sql/mdl.h
index 05a0b44dc9b..d43548fb65f 100644
--- a/sql/mdl.h
+++ b/sql/mdl.h
@@ -466,13 +466,14 @@ public:
   void destroy();
 
   bool try_acquire_lock(MDL_request *mdl_request);
-  bool acquire_lock(MDL_request *mdl_request);
-  bool acquire_locks(MDL_request_list *requests);
-  bool upgrade_shared_lock_to_exclusive(MDL_ticket *mdl_ticket);
+  bool acquire_lock(MDL_request *mdl_request, ulong lock_wait_timeout);
+  bool acquire_locks(MDL_request_list *requests, ulong lock_wait_timeout);
+  bool upgrade_shared_lock_to_exclusive(MDL_ticket *mdl_ticket,
+                                        ulong lock_wait_timeout);
 
   bool clone_ticket(MDL_request *mdl_request);
 
-  bool wait_for_lock(MDL_request *mdl_request);
+  bool wait_for_lock(MDL_request *mdl_request, ulong lock_wait_timeout);
 
   void release_all_locks_for_name(MDL_ticket *ticket);
   void release_lock(MDL_ticket *ticket);
@@ -644,7 +645,7 @@ private:
   MDL_ticket *find_ticket(MDL_request *mdl_req,
                           bool *is_transactional);
   void release_locks_stored_before(MDL_ticket *sentinel);
-  bool acquire_lock_impl(MDL_request *mdl_request);
+  bool acquire_lock_impl(MDL_request *mdl_request, ulong lock_wait_timeout);
 
   bool find_deadlock();
 
@@ -680,8 +681,7 @@ private:
     mysql_mutex_unlock(&m_signal_lock);
   }
 
-  mdl_signal_type wait();
-  mdl_signal_type timed_wait(ulong timeout);
+  mdl_signal_type timed_wait(struct timespec *abs_timeout);
 
   mdl_signal_type peek_signal()
   {