WorkflowPersistenceService Class

When certain conditions occur while the workflow is running, the workflow runtime engine persists state information about the workflow instance. Persistence can occur, for example, when an atomic transaction finishes, when the workflow instance becomes idle, when the host calls WorkflowInstance.Unload on the workflow instance, or when a workflow instance is terminated or finishes. When the workflow runtime engine semantics dictate that persistence should occur, the workflow runtime engine calls methods that are supplied by a persistence service to save state information about the workflow instance. Likewise, when the workflow runtime engine needs to restore a previously persisted workflow instance, it calls methods that are supplied by the persistence service to load this state information. The workflow runtime engine handles all the semantics regarding when to perform persistence. The persistence service handles actually saving and loading the workflow state information to or from a data store.

You can create a persistence service by deriving a class from the WorkflowPersistenceService class. You can add your persistence service to the workflow runtime engine by calling AddService or by making an appropriate entry in the application configuration file. The WorkflowRuntime should only contain one persistence service. Windows Workflow Foundation provides the SqlWorkflowPersistenceService class, an out-of-box persistence service, which you can use as is or extend.

The workflow runtime engine has semantics for locking workflow state information for use in environments where persistence services that run in different processes might have access to a single data store. The WorkflowPersistenceService class provides the capability to support this functionality of the workflow runtime engine by providing a parameter to SaveWorkflowInstanceState that specifies whether the state information of a workflow instance should be unlocked in the data store, and by providing a method UnlockWorkflowInstanceState to unlock previously locked workflow state information. In a persistence service that implements locking, a call to LoadWorkflowInstanceState should lock the state information for a workflow instance.

Your persistence service should throw a PersistenceException if it fails to save state information to its data store or load state information from its data store. The workflow runtime engine expects this behavior.

A batching mechanism is provided for services that use a durable store to save workflow state information. It is important in these cases to maintain consistency between the durable store that is used by the persistence service and the internal state of the workflow runtime engine. You can add functionality defined by the IPendingWork interface to your service, and then participate in workflow transaction batching provided by the WorkflowCommitWorkBatchService by adding changes to your data store as work items to the WorkBatch. The durable store itself should implement the IEnlistmentNotification interface, so that workflow information is not persisted incorrectly in the event of a transaction rollback. For more information, see SaveCompletedContextActivity or SaveWorkflowInstanceState.

.NET Framework

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference