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GUIDELINE
Using Shared Objects
ABAP_BACKGROUND Access to shared objects is regulated by lock mechanisms. The individual locks are stored as administrative information with the area instances in the shared memory and are set and evaluated when they are accessed using area handles.
ABAP_RULE Shared buffer and exclusive buffer are suitable application scenarios for shared objects. The access to shared objects should be wrapped in loader and broker classes.
ABAP_DETAILS How locks work depends on how shared objects are used as follows:
Scenario 1 - Use as a shared buffer A shared buffer is a data store that is rarely changed (once a day up to a maximum of once an hour), usually by a single user only. The amount of data can be very large. In general, many users have read access to a shared buffer at the same time. A typical use of a shared buffer is to store a catalog.
Scenario 2 - Use as an exclusive buffer An exclusive buffer is a data store that is read or write accessed by one user only, or in rare cases, by one user with write access and another with read access. The data stored in an exclusive buffer should be available longer term, that is, longer than a programs lifetime. A typical use of an exclusive buffer is to store a shopping basket that is filled initially by the shopper and then read by the salesperson later. General shared memory programming is not possible. The current lock logic does not enable you to set specific locks for the following requirements:
Many parallel read and write accesses
Frequent write accesses
Division into changeable and non-changeable areas Although the lock logic makes the first two points technically possible, they are not practical because most accesses would be rejected.
Wrapping It is recommended that application programs do not access the shared objects memory directly. Instead (read) accesses to the shared objects should be wrapped in a wrapping class, whose methods are accessed by the individual programs. The area constructor class can be used as the wrapping class, for example. Wrapping has the following advantages:
Central administration of an area in the shared memory
An application program does not need to worry about area handles and locks.
