[Code] Lock Mechanism

Lock:

CALL FUNCTION 'ENQUEUE_E_TRDIR'
  EXPORTING
    name           = 'PROGRAM_RUNNING'
    _scope         = '1'
  EXCEPTIONS
    foreign_lock   = 1
    system_failure = 2
    OTHERS         = 3.
IF sy-subrc <> 0.
  CALL FUNCTION 'DEQUEUE_ALL'.
  MESSAGE e000(zsd01) WITH 'Err: Program running!'.
ENDIF.

Unlock:

CALL FUNCTION 'DEQUEUE_ALL'.

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Reference Manual:

http://help.sap.com/saphelp_nwpi71/helpdata/EN/cf/21eed9446011d189700000e8322d00/frameset.htm