Syntax
------ 
IS_USED_LOCK(str)
 
Description
----------- 
Checks whether the lock named str is in use (that is,
locked). If so,
it returns the connection identifier of the client that
holds the
lock. Otherwise, it returns NULL. str is case insensitive.
 
If the metadata_lock_info plugin is installed, the
Information Schema metadata_lock_info table contains
information about locks of this kind (as well as metadata
locks).
 
Statements using the IS_USED_LOCK() function are not safe
for replication.
 


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