topic Re: Shared Memory - handling cx_shm_build_failed exception in Application Development and Automation Discussions

Shared Memory - handling cx_shm_build_failed exception

jiri_medved — Mon, 23 Nov 2020 16:10:08 GMT

Hello Experts,

I use shared memory for caching personal data from external system. The build method looks like following

METHOD if_shm_build_instance~build.

* Autoload of SHMO (first time use, after system restart and so on)

  DATA: lcl_ldap TYPE REF TO zcl_ldap,
        lcl_ldap_root TYPE REF TO zcl_ldap_root,
        lx_exception TYPE REF TO cx_root.

  TRY.
      lcl_ldap = zcl_ldap=>attach_for_write( ).
    CATCH cx_shm_error INTO lx_exception.
      RAISE EXCEPTION TYPE cx_shm_build_failed
        EXPORTING
          previous = lx_exception.
  ENDTRY.

  TRY.
      CREATE OBJECT lcl_ldap_root AREA HANDLE lcl_ldap.
      lcl_ldap->set_root( lcl_ldap_root ).
      lcl_ldap_root->set_staff( ).
      lcl_ldap->detach_commit( ).
    CATCH cx_shm_error zcx_ldap_not_reachable
      INTO lx_exception.
      RAISE EXCEPTION TYPE cx_shm_build_failed
        EXPORTING
          previous = lx_exception.
  ENDTRY.

  IF invocation_mode = cl_shm_area=>invocation_mode_auto_build.
    CALL FUNCTION 'DB_COMMIT'.
  ENDIF.

the method set_staff( ) gets the data from an external system and populates the shared memory. It raises ZCX_LDAP_NOT_REACHABLE if calling the external system fails.

In the main program I attach the shared memory like following:

...
  DO 10 TIMES.
    TRY.
        lcl_ldap_shmo = zcl_ldap=>attach_for_read( ).
      CATCH cx_shm_inconsistent.
        zcl_ldap=>free_area( ).
      CATCH cx_shm_no_active_version
      cx_shm_read_lock_active
      cx_shm_change_lock_active
      cx_shm_exclusive_lock_active
      INTO lv_exception.
    ENDTRY.

    IF lcl_ldap_shmo IS NOT INITIAL.
      EXIT.
    ENDIF.
    WAIT UP TO 2 SECONDS.
  ENDDO.
...

It works fine if no exception is raised in the set_staff() method.

But if ZCX_LDAP_NOT_REACHABLE is raised the ATTACH_FOR_READ method raises CX_SHM_NO_ACTIVE_VERSION exception and there is a short dump of uncaught exception CX_SHM_BUILD_FAILED in ST22.

How can I catch the exception in order to avoid the short dump?

Re: Shared Memory - handling cx_shm_build_failed exception

nmirandaghn — Mon, 23 Nov 2020 17:49:32 GMT

Add the exception ZCX_LDAP_NOT_REACHABLE to the CATCH block.

Hope it helps.

    TRY.
        lcl_ldap_shmo = zcl_ldap=>attach_for_read( ).
      CATCH cx_shm_inconsistent.
        zcl_ldap=>free_area( ).
      CATCH cx_shm_no_active_version
      cx_shm_read_lock_active
      cx_shm_change_lock_active
      cx_shm_exclusive_lock_active 
      zcx_ldap_not_reachable " <--- Exception added
      INTO lv_exception.
    ENDTRY.

Re: Shared Memory - handling cx_shm_build_failed exception

jiri_medved — Mon, 23 Nov 2020 17:55:22 GMT

Unfortunately that does not work.

Re: Shared Memory - handling cx_shm_build_failed exception

nmirandaghn — Mon, 23 Nov 2020 18:02:45 GMT

What about if you add CX_ROOT exception to the CATCH block?

This exception will catch any exception.

Re: Shared Memory - handling cx_shm_build_failed exception

jiri_medved — Tue, 24 Nov 2020 09:39:07 GMT

I went through several SAP standard implementations of the interface IF_SHM_BUILD_INSTANCE. I could not find any common clear pattern in these implementations how to implement the method BUILD in the "right" way. I have noticed though that none of the implementations throw an exception in case the set method is not succesful.

I have modified my implementation in the following way.

METHOD if_shm_build_instance~build.

* Autoload of SHMO (first time use, after system restart and so on)

  DATA: lcl_ldap TYPE REF TO zcl_ldap,
        lcl_ldap_root TYPE REF TO zcl_ldap_root,
        lx_exception TYPE REF TO cx_root.

  TRY.
      lcl_ldap = zcl_ldap=>attach_for_write( ).
      CREATE OBJECT lcl_ldap_root AREA HANDLE lcl_ldap.
      lcl_ldap->set_root( lcl_ldap_root ).
    CATCH cx_shm_error
      INTO lx_exception.
      RAISE EXCEPTION TYPE cx_shm_build_failed
        EXPORTING
          previous = lx_exception.
  ENDTRY.

  TRY.
      lcl_ldap_root->set_staff( ).
  CATCH zcx_ldap_not_reachable.
      lcl_ldap->detach_rollback( ).
      RETURN.
  ENDTRY.

  TRY .
      lcl_ldap->detach_commit( ).
    CATCH cx_shm_error INTO lx_exception.
      RAISE EXCEPTION TYPE cx_shm_build_failed
        EXPORTING
          previous = lx_exception.
  ENDTRY.

  IF invocation_mode = cl_shm_area=>invocation_mode_auto_build.
    CALL FUNCTION 'DB_COMMIT'.
  ENDIF.
ENDMETHOD.

I am not sure if my implementation is 100% correct but it works - there are no short dumps in ST22 even if the third party system is not reachable.

Re: Shared Memory - handling cx_shm_build_failed exception

jiri_medved — Tue, 24 Nov 2020 09:44:16 GMT

I can catch the exception cx_shm_no_active_version. But there is always short dump in ST22. The auto build of the shared memory is executed in a separate thread and the exception is not propagated to the calling thread.

I have found a workable solution - see my answer. Any comments highly welcomed.