How to check the status of a user defined lock using the IS_FREE_LOCK() function?

IS_FREE_LOCK(lock) is a MySQL built-in function that returns 1 if a given user lock is free, 0 otherwise. For example:

SELECT GET_LOCK('MyLock', 60), IS_FREE_LOCK('MyLock');
  -- +------------------------+------------------------+
  -- | GET_LOCK('MyLock', 60) | IS_FREE_LOCK('MyLock') |
  -- +------------------------+------------------------+
  -- |                      1 |                      0 |
  -- +------------------------+------------------------+

SELECT RELEASE_LOCK('MyLock'), IS_FREE_LOCK('MyLock');
  -- +------------------------+------------------------+
  -- | RELEASE_LOCK('MyLock') | IS_FREE_LOCK('MyLock') |
  -- +------------------------+------------------------+
  -- |                      1 |                      1 |
  -- +------------------------+------------------------+

Reference information of the IS_FREE_LOCK() function:

IS_FREE_LOCK(lock): boolean
  Returns 1 if a given user lock is free, 0 otherwise.

Arguments, return value and availability:
  lock: Required. The lock name to be examined.
  boolean: Return value. 1 if the lock is free, 0 otherwise.
  Available since MySQL 4.

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