ABAP_to_the_Future

14
Shared Memory
RAISE EXCEPTION TYPE cx_shm_build_failed
EXPORTING
previous = lo_exception.
ENDTRY.
"Read the database and fill up the internal table
TRY.
"The broker class is sometimes called a "handle"
"as in 'Handle and Gretel'
CREATE OBJECT lo_root AREA HANDLE lo_broker.
lo_broker->set_root( lo_root ).
lo_root->load_monsters( ).
lo_broker->detach_commit( ).
CATCH cx_shm_error INTO lo_exception.
RAISE EXCEPTION TYPE cx_shm_build_failed
EXPORTING
previous = lo_exception.
ENDTRY.
IF invocation_mode = cl_shm_area=>invocation_mode_auto_build.
CALL FUNCTION 'DB_COMMIT'.
ENDIF.
ENDMETHOD."Build
Listing 14.6 Coding the BUILD Method
Most of the code in Listing 14.6 is stra ightforward enough, but notice how the
instance of the root class is created. Instead of a normal CREATE OBJECT statement,
which creates the instance in the memory of the running prog ram, there is the
AREA HANDLE addition, which means that instead the instance is created in shared
memory and stays there even after the calling program ends.
The other point to note is the DETACH_COMMIT method. For a transactional shared
memory area (such as the one in this example), the shared memory area only gets
updated once a COMMIT WORK occurs, which makes updating the shared memory
part of a logical unit of work fall under the “all shall change or none shall change”
principle. For a nontransactional area, DETACH_COMMIT updates the shared memory
at once.
In any event, as can be seen during a build, a DB_COMMIT function is called to
ensure that both types of shared memory area are updated. The build is running
in a separate session, so the COMMIT can have no side effects.
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