SAP ABAP - Locking

What Is Locking ?
When two users simultaneously attempt to access the same data record, this is synchronised by a lock mechanism.

When dialog transactions are programmed, locks are set and released by calling certain function modules. These function modules are generated automatically from the definition of so-called lock objects in the ABAP/4 Dictionary.

To synchronize the access to a table by setting and removing locks, a Lock object has to be defined in the ABAP/4 Dictionary. Activating the lock object automatically creates function modules for setting and removing locks. These function modules must be included when programming interactive transactions.

Lock Mechanism :

To set locks, a lock object must be defined in the ABAP/4 Dictionary. In this lock object, those tables in which data records are to be locked by calling a lock are determined. All tables included in a lock object must be connected to each other via foreign keys. The key fields of the tables in a lock object form the Lock arguments for the tables. The lock arguments are the basis for formulating the logical condition for identifying the records to be locked.

SAP provides you with the ability to restrict access to data while the table is being updated. This is fairly simple to implement via the use of a lock object (Created in SE11). 

Step 2 - ABAP code to lock table entries
Add the following code in-order to create the table lock. This function module must be called 
before any update takes place. If a lock has already been taken out it will display the appropriate message. 


before any update takes place. If a lock has already been taken out it will display the appropriate message. 

  CALL FUNCTION 'ENQUEUE_EZ_ZTABLENAME'

      EXPORTING

           mode_ZTABLENAME = 'E'  "E = Write Lock, S = Read Lock, X = Exclusive not cumulative

           mandt              = sy-mandt

           KEYFIELD1           = "Value

           KEYFIELD2           = "Value

           KEYFIELD3           = "Value

                   ...

*         X_KEYFIELD1            = ' '

*         X_KEYFIELD2            = ' '

*         X_KEYFIELD3            = ' '

                   ...

*         _SCOPE             = '2'

*         _WAIT              = ' '

*         _COLLECT           = ' '

*   If exceptions are not used, message is displayed within FM

    EXCEPTIONS

         FOREIGN_LOCK       = 1

         SYSTEM_FAILURE     = 2

         OTHERS             = 3.

  IF sy-subrc <> 0.

*   Retrieve message displayed within Function Module

    message id     sy-msgid

              type   'I'

              number sy-msgno

              with   sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.

    EXIT.

  ENDIF.

Step 3 - ABAP code to Remove table lock(s)
The following code will remove the lock for the specific table entries. 

CALL FUNCTION 'DEQUEUE_EZ_ZTABLENAME'

    EXPORTING

         MODE_ZTABLENAME = 'E'

         MANDT              = SY-MANDT

           mandt              = sy-mandt

           KEYFIELD1           = "Value

           KEYFIELD2           = "Value

           KEYFIELD3           = "Value

                   ...

    *         X_KEYFIELD1            = ' '

    *         X_KEYFIELD2            = ' '

    *         X_KEYFIELD3            = ' '

                   ...

*         _SCOPE             = '3'

*         _SYNCHRON          = ' '

*         _COLLECT           = ' '