How to synchronize concurrent access to static data in ABAP Objects

Question

Hi,
1) First of all I mwould like to know the scope of static (class-data) data of an ABAP Objects Class: If changing a static data variable is that change visible to all concurrent processes in the same Application Server?
2) If that is the case. How can concurrent access to such data (that can be shared between many processes) be controlled. In C one could use semaphores and in Java Synchronized methods and the monitor concept. But what controls are available in ABAP for controlling concurrent access to in-memory data?
Many thanks for your help!
Regards,
Christian

Answer 1

Hello Christian
Here is an example that shows that the static attributes of a class are not shared between two reports that are linked via SUBMIT statement.
*& Report  ZUS_SDN_OO_STATIC_ATTRIBUTES
REPORT  zus_sdn_oo_static_attributes.
DATA:
  gt_list        TYPE STANDARD TABLE OF abaplist,
  go_static      TYPE REF TO zcl_sdn_static_attributes.
<i>* CONSTRUCTOR method of class ZCL_SDN_STATIC_ATTRIBUTES:
**METHOD constructor.
*** define local data
**  DATA:
**    ld_msg    TYPE bapi_msg.
**  ADD id_count TO md_count.
**ENDMETHOD.
* Static public attribute MD_COUNT (type i), initial value = 1</i>
PARAMETERS:
  p_called(1)  TYPE c  DEFAULT ' ' NO-DISPLAY.
START-OF-SELECTION.
<b>* Initial state of static attribute:
*    zcl_sdn_static_attributes=>md_count = 0</b>
  syst-index = 0.
  WRITE: / syst-index, '. object: static counter=',
           zcl_sdn_static_attributes=>md_count.
  DO 5 TIMES.
<b>*   Every time sy-index is added to md_count</b>
    CREATE OBJECT go_static
      EXPORTING
        id_count = syst-index.
    WRITE: / syst-index, '. object: static counter=',
             zcl_sdn_static_attributes=>md_count.
<b>*   After the 3rd round we start the report again (via SUBMIT)
*   and return the result via list memory.
*   If the value of the static attribute is not reset we would
*   start with initial value of md_count = 7 (1+1+2+3).</b>
    IF ( p_called = ' '  AND
         syst-index = 3 ).
      SUBMIT zus_sdn_oo_static_attributes EXPORTING LIST TO MEMORY
        WITH p_called = 'X'
      AND RETURN.
      CALL FUNCTION 'LIST_FROM_MEMORY'
        TABLES
          listobject = gt_list
        EXCEPTIONS
          not_found  = 1
          OTHERS     = 2.
      IF sy-subrc <> 0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
*         WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
      ENDIF.
      CALL FUNCTION 'DISPLAY_LIST'
*       EXPORTING
*         FULLSCREEN                  =
*         CALLER_HANDLES_EVENTS       =
*         STARTING_X                  = 10
*         STARTING_Y                  = 10
*         ENDING_X                    = 60
*         ENDING_Y                    = 20
*       IMPORTING
*         USER_COMMAND                =
        TABLES
          listobject                  = gt_list
        EXCEPTIONS
          empty_list                  = 1
          OTHERS                      = 2.
      IF sy-subrc <> 0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
*         WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
      ENDIF.
    ENDIF.
  ENDDO.
<b>* Result: in the 2nd run of the report (via SUBMIT) we get
*         the same values for the static counter.</b>
END-OF-SELECTION.
Regards
  Uwe