DESKTOP FRAMEWORKS CONCEPTS - Concurrency and hierarchical locking

Concurrency and hierarchical locking

The Compound Document framework provides a hierarchical locking scheme for the persistent data objects:

Document component
Model
Presenter state

A locked component locks all of its child components and all of its parent document components. The CommonPoint application system provides two varieties of document component monitor entries to lock the component for reading or for reading and writing.

The component monitor entries are:

TDocumentComponentWriteEntry--The model and/or presenter state of a component can be looked up for reading as long as a TDocumentComponentReadEntry object exists for the component. Multiple readers are allowed.
TDocumentComponentReadEntry--The model or presenter state of a component can be looked up for writing as long as a TDocumentComponentWriteEntry object exists for the component. Only a single writer is allowed.

Persistence of lock

Component entries take a component reference (TModelPointerTo) and, while they exist, the component and all of the component's data (including any embedded components it might have) remain locked.

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