org.azyva.dragom.model.config

Interface OptimisticLockHandle

public interface OptimisticLockHandle

Represents an optimistic lock held on an entity.

See Optimistic concurrency control for a general discussion about optimistic locking.

In Dragom, optimistic locking is used mainly by MutableNodeConfig and MutableNode, the latter being what is generally seen by applications using Dragom.

The idea is that an application that allow modifying the configuration data underlying a Model is expected to the Node's to the user in a hierarchical manner, allowing him to edit their properties on a Node by Node basis. The user can look at Node properties, modify them and then save the changes. At that point it is pertinent to ensure that the same Node properties have not been changed by another user. To do that, the application obtains an OptimisticLockHandle representing the state of the Node data. When saving the data, it provides the same OptimisticLockHandle which allows the object to validate the state of the data has not changed since it was read.

Typically, a last modification timestamp or unique revision number is maintained within an OptimisticLockHandle implementation.

An OptimisticLockHandle is mutable. When configuration data is saved successfully (the state of the OptimisticLockHandle corresponds to the state of the data it represents), it is updated to reflect the new state of the data so that the caller can save changed data repetitively withouth having to read them again.

Optimistic locking is managed externally to NodeConfigTransferObject, even though the data represented by an OptimisticLockHandle is generally the state of a NodeConfigTransferObject. The reason is to support the fact that applications manage multiple independent groups of properties for a given Node, for which independent NodeConfigTransferObject's are typically managed. But when one is saved, it must not rendre the lock representing the others since they all relate to the same conversation the user has. The caller can therefore obtain a single OptimisticLockHandle that it shares among the multiple groups of data.

Author:

David Raymond

Method Summary

Modifier and Type	Method and Description
void	clearLock() Clears the lock.
boolean	isLocked() Indicates if the OptimisticLockHandle is actually locked, meaning that it represents some state.

Method Detail

isLocked

boolean isLocked()

Indicates if the OptimisticLockHandle is actually locked, meaning that it represents some state.

An OptimisticLockHandle that is not locked is expected to get automatically locked to the state of data that is obtained (using a "get" method).

Returns:

Indicates if the OptimisticLockHandle is locked.

clearLock

void clearLock()

Clears the lock.