Syntax

1. *&---------------------------------------------------------------------*
   *& Report DEMO_OPT_ENQUEUE
   *&
   *&---------------------------------------------------------------------*
   *& Demo program for optimistic locks
   *&
   *& Besides the old lock modes
   *& - Non cumulative lock Mode = 'X'
   *& - Exclusive lock Mode = 'E'
   *& - Shared lock Mode = 'S'
   *&
   *& a new lock mode is introduced
   *& - Optimistic lock Mode = 'O'
   *& - Mode 'R' for pRomoting an 'O' lock into an 'E' lock
   *& Mode 'R' does not appear in the lock table
   *&
   *& See MODE_xxx-Parameter of the ENQUEUE_xxx FMs
   *&
   *& An optimistic lock is similar to a shared lock 'S'
   *& The differences are the following:
   *&
   *& - it can be promoted to an exclusive lock (mode 'E'),
   *& if there is no collision
   *& The promotion of n optimistic lock collides with
   *& - a shared lock 'S' which didn't collide with the 'O' lock
   *& but collides with the resulting 'E' lock
   *& - an own lock becomes a foreign lock due to passing it to the
   *& update
   *&
   *& - The successful promotion of an optimistic lock to an exclusive lock
   *& deletes all foreign optimistic locks which collide with the
   *& generated 'E' lock.
   *&
   *& - the optimistic lock can get lost due to the promotion of a
   *& foreign 'O' lock (see above).
   *&
   *& Optimistic locks are compatible to the known lock modes.
   *& Programs using ordinary pessimistic locks can coexist with programs
   *& that switched to optimistic locking and use the same
   *& Lock Objects and Enqueue function modules.
   *& You don't need to switch all programs at the same time
   *& Please take care of side effects!
   *&
   *& The existing ENQUEUE_xxx and DEQUEUE_xxx function modules can also
   *& be used for otimistic locks.
   *&
   *&---------------------------------------------------------------------*
   REPORT DEMO_OPT_ENQUEUE.
   DATA: lock_mode_opt type enqmode value 'O'.
   DATA: lock_mode_excl type enqmode value 'E'.
   DATA: lock_mode_opt_to_excl type enqmode value 'R'.
   *-----------------------------------------------------------------------
   * Set optimistic lock.
   * The operation is successful when there is no collision with foreign
   * 'E' and 'X' locks.
   *-----------------------------------------------------------------------
   CALL FUNCTION 'ENQUEUE_ENQ_SFLIGHT'
   EXPORTING
   MODE_SFLIGHT = lock_mode_opt
   EXCEPTIONS
   FOREIGN_LOCK = 1
   SYSTEM_FAILURE = 2
   OTHERS = 3.
   IF SY-SUBRC <> 0.
   MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
   WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
   ENDIF.
   *-----------------------------------------------------------------------
   * Promote optimistic lock into exclusive lock.
   * The operation is successful, if
   * - the own 'O' lock still exists
   * - there is no collision of the new 'E' lock with foreign locks
   *-----------------------------------------------------------------------
   CALL FUNCTION 'ENQUEUE_ENQ_SFLIGHT'
   EXPORTING
   MODE_SFLIGHT = lock_mode_opt_to_excl
   EXCEPTIONS
   FOREIGN_LOCK = 1
   SYSTEM_FAILURE = 2
   OTHERS = 3.
   IF SY-SUBRC <> 0.
   MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
   WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
   ENDIF.
   *-----------------------------------------------------------------------
   * Release exclusive lock
   *-----------------------------------------------------------------------
   CALL FUNCTION 'DEQUEUE_ENQ_SFLIGHT'
   EXPORTING
   MODE_SFLIGHT = lock_mode_excl.