How to use Lock Objects in ABAP

Let say we have a customized table ZCUST_INFO that holds a specific customer information with MANDT(client number) and KUNNR(customer number) as the key field.

So let's create a Lock Object for our customized table:
1. Go to transaction SE11
2. Click on Lock Object radio button and type-in EZCUST_INFO on name field and click on create button.
3. On Tables Tab, type-in ZCUST_INFO on name field and choose Write Lock on Lock Mode.
4. Go to Lock Parameter Tab and on the first row, type-in mandt on lock parameter, zcust_info on
table, and mandt on field.
5. On second row, type-in custnum on lock parameter, zcust_info on table, and kunnr on field.
6. Click save and activate.

Now let say we also have a dialog program for managing this the content of this table. We have screen 100 for our selection screen with customer number as selection parameter, screen 200 for editing screen, and screen 300 for display screen.

On the PBO of screen 200, let's add the code below.

CALL FUNCTION 'ENQUEUE_EZCUST_INFO'
EXPORTING
MODE_ZCUST_INFO = 'X'
MANDT = sy-mandt
CUSTNUM = <customer number from screen 100>
EXCEPTIONS
FOREIGN_LOCK = 1
SYSTEM_FAILURE = 2
OTHERS = 3.
IF sy-subrc = 1.
MESSAGE 'This record is currently locked by another user!' type 'I'.
leave to screen 300.
ENDIF.

The code above will request for lock on the table zcust_info specifically on the record specified on
the mandt and custnum parameter. If the record is already locked by another user, the user will be
prompted and will be redirected to screen 300 which is the display screen.

Lastly, on the PAI of screen 200, add the code below to release and unlock the object queued on the PBO:

CALL FUNCTION 'DEQUEUE_EZCUST_INFO'
EXPORTING
MODE_ZCUST_INFO = 'X'
MANDT = sy-mandt
CUSTNUM = <customer number from screen 100>
EXCEPTIONS
FOREIGN_LOCK = 1
SYSTEM_FAILURE = 2
OTHERS = 3.