ABAP_to_the_Future

14
Shared Memory
class, and once you have that you can accessthe root class within the broker to get
your monster data.
DATA: lt_monsters TYPE STANDARD TABLE OF ztvc_monsters,
lo_monster TYPE REF TO zcl_monster_shmo.
DO 10 TIMES.
TRY.
"We create an instance of the broker class which
"contains within it a reference to the instance of
"the root class which lives in shared memory
"A (non exclusive) read lock is also set
lo_monster = zcl_monster_shmo=>attach_for_read( ).
"The root class contains our custom methods
lt_monsters[] = lo_monster->root->get_monsters( ).
"Release read lock ; ending the transaction would
"have the same result
lo_monster->detach( ).
EXIT."From Do-End-Do
CATCH cx_shm_no_active_version.
“The root instance has not been created – the BUILD
“method will be called asynchronously
"If after ten seconds the object has not initialised itself we
"give up
WAIT UP TO 1 SECONDS. "Takes a while to load up
CONTINUE. "With do-end-do
CATCH cx_shm_inconsistent "Root class is out of date
cx_shm_exclusive_lock_active "Someone trying to change
cx_shm_change_lock_active "Someone trying to change data
cx_shm_read_lock_active. "Amazingly, this can be an error
EXIT. "From do-end-do, we will use a real database read
ENDTRY.
ENDDO.
Listing 14.4 A Shared Memory Read Request
As is normal in programming, you can see that the bulk of the code in Listing 14.4
is in regard to error handling. There are two possible error situations:
왘 Another user may have the instance of the root class locked in such a way that
you’re not allowed access; someone may bein the middle of changing the data,
for example. In this case, it’s better to read the database directly. The calling
class is in the persistency layer, so reading from the database is not outside its
job description.
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