UIDs and Sharing

All KcsLoadable classes have unique identifiers (UIDs). The combination of a chunkSet and a chunkId allows you to save the state of KcsLoadable derivatives for later use. To do this, either minimize and regenerate by calling unload() and load(), or save the UID of the instance and reallocate the instance with the UID-based constructor.

Because classes that contain other loadable objects use the same chunkSet, you must save the chunkId within your own data store. To explain this further, an example with an KcsXform class is used; see Chapter 7, KcsXform Derivative for more information. For example, a sequence transformation saves its array of transform chunkIds in the same chunkset as it does its own state. The KcsXformSeq class has an array of pointers to KcsXforms when it is allocated in memory.

Since all of these transforms have unique identifiers, the KcsXformSeq class places the UID of each transform in an array and saves it. Once this sequence is constructed and told to load, (the chunkId is passed into the constructor) it gets the chunk and, for each transform chunkId, it calls the KcsXform::createXform(uid)() constructor. This constructor allocates the transform associated with that chunkId.

All loadable derivatives should support construction based on this chunkSet and chunkId combination. Loadable objects are shared by using a UID map table kept in the static KcsLoadable data member. When a new loadable object is created, this UID map table is searched first to see if an object with a particular ChunkSet and ChunkId has already been instantiated. If so, the pointer to that object is returned; if not, a new object is created and entered into the table.