Defines contracts for transactional and concurrent access to cached entity and collection data.

Transactions pass in a timestamp indicating transaction start time which is then used to protect against concurrent access. Exactly how that happens is based on the actual access-strategy implementation used.

Two different implementation patterns are provided for:

• A transaction-aware cache implementation might be wrapped by a synchronous access strategy, where updates to the cache are written to the cache inside the transaction.
• A non-transaction-aware cache would be wrapped by an asynchronous access strategy, where items are merely "soft locked" during the transaction and then updated during the "after transaction completion" phase. The soft lock is not an actual lock on the database row, it only prevents access to the cached representation of the item.

The asynchronous access strategies are: read-only, read-write and nonstrict-read-write. The only synchronous access strategy is transactional.

Note that:

• for an asynchronous cache, cache invalidation must be a two-step process ("lock" then "unlock", or "lock" then "after update"), since this is the only way to guarantee consistency with the database for a non-transactional cache implementation, but
• for a synchronous cache, cache invalidation may be performed in a single operation ("evict" or "update").

Hence, the contracts org.hibernate.cache.spi.access.EntityDataAccess and org.hibernate.cache.spi.access.CollectionDataAccess define a three-step process to allow for both models (see the individual contracts for details).

Note that query result caching does not go through an access strategy; those caches are managed directly against the underlying org.hibernate.cache.spi.QueryResultsRegion.