-----------------+
| GET_LOCK('lock3',10) |
+----------------------+
|                    1 |
+----------------------+

SELECT GET_LOCK('lock3',10);
+----------------------+
| GET_LOCK('lock3',10) |
+----------------------+
|                    1 |
+----------------------+

SELECT * FROM INFORMATION_SCHEMA.METADATA_LOCK_INFO;
+-----------+---------------------+---------------+-----------+--------------+-
----------+
| THREAD_ID | LOCK_MODE           | LOCK_DURATION | LOCK_TYPE | TABLE_SCHEMA |
TABLE_NAME |
+-----------+---------------------+---------------+-----------+--------------+-
----------+
|        46 | MDL_SHARED_NO_WRITE | NULL          | User lock | lock3        |
     |
+-----------+---------------------+---------------+-----------+--------------+-
----------+

SELECT RELEASE_LOCK('lock3');
+-----------------------+
| RELEASE_LOCK('lock3') |
+-----------------------+
|                     1 |
+-----------------------+

SELECT * FROM INFORMATION_SCHEMA.METADATA_LOCK_INFO;
+-----------+---------------------+---------------+-----------+--------------+-
----------+
| THREAD_ID | LOCK_MODE           | LOCK_DURATION | LOCK_TYPE | TABLE_SCHEMA |
TABLE_NAME |
+-----------+---------------------+---------------+-----------+--------------+-
----------+
|        46 | MDL_SHARED_NO_WRITE | NULL          | User lock | lock3        |
     |
+-----------+---------------------+---------------+-----------+--------------+-
----------+

SELECT RELEASE_LOCK('lock3');
+-----------------------+
| RELEASE_LOCK('lock3') |
+-----------------------+
|                     1 |
+-----------------------+

SELECT * FROM INFORMATION_SCHEMA.METADATA_LOCK_INFO;
Empty set (0.000 sec)

Timeout example: Connection 1:

SELECT GET_LOCK('lock4',10);
+----------------------+
| GET_LOCK('lock4',10) |
+----------------------+
|                    1 |
+----------------------+

Connection 2:

SELECT GET_LOCK('lock4',10);

After 10 seconds...

+----------------------+
| GET_LOCK('lock4',10) |
+----------------------+
|                    0 |
+----------------------+

Deadlocks are automatically detected and resolved. Connection 1:

SELECT GET_LOCK('lock5',10); 
+----------------------+
| GET_LOCK('lock5',10) |
+----------------------+
|                    1 |
+----------------------+

Connection 2:

SELECT GET_LOCK('lock6',10);
+----------------------+
| GET_LOCK('lock6',10) |
+----------------------+
|                    1 |
+----------------------+

Connection 1:

SELECT GET_LOCK('lock6',10); 
+----------------------+
| GET_LOCK('lock6',10) |
+----------------------+
|                    0 |
+----------------------+

Connection 2:

SELECT GET_LOCK('lock5',10);
ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting
transaction

URL: https://mariadb.com/kb/en/get_lock/https://mariadb.com/kb/en/get_lock/