The lock_id function
copies a locker ID, which is guaranteed to be unique in the specified lock
table, into the memory location referenced by idp.
The lock_id function returns a non-zero error value on failure and 0 on success.
Errors
The lock_id function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
If a catastrophic error has occurred, the lock_id function may fail and return
DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail
in the same way.