【IT168技术文档】

  我们除了使用WF提供的SqlWorkflowPersistenceService外，还可以自定义持久化服务。因为有的时候你可能不想使用Sql Server数据库，我们就可以通过自定义持久化服务来使用其他的数据库，文件等来进行持久化存储。

  当从内存中卸载工作流时，工作流运行时可使用该服务将工作流实例状态保存到文件。该持久服务类代码如下FilePersistence.cs：

 public class FilePersistenceService : WorkflowPersistenceService
{
public readonly static TimeSpan MaxInterval = new TimeSpan(30, 0, 0, 0);
private bool unloadOnIdle = false;
private Dictionary<Guid,Timer> instanceTimers;
public FilePersistenceService(bool unloadOnIdle)
{
this.unloadOnIdle = unloadOnIdle;
this.instanceTimers = new Dictionary<Guid, Timer>();
}
protected override void SaveWorkflowInstanceState(Activity rootActivity, bool unlock)
{
// Save the workflow 
            Guid contextGuid = (Guid)rootActivity.GetValue(Activity.ActivityContextGuidProperty);
Console.WriteLine("Saving instance: {0}\n", contextGuid);
SerializeToFile( WorkflowPersistenceService.GetDefaultSerializedForm(rootActivity), contextGuid);
// See when the next timer (Delay activity) for this workflow will expire 
            TimerEventSubscriptionCollection timers = (TimerEventSubscriptionCollection)rootActivity.GetValue(TimerEventSubscriptionCollection.TimerCollectionProperty);
TimerEventSubscription subscription = timers.Peek();
if (subscription != null)
{
// Set a system timer to automatically reload this workflow when its next timer expires 
                TimerCallback callback = new TimerCallback(ReloadWorkflow);
TimeSpan timeDifference = subscription.ExpiresAt - DateTime.UtcNow;
// check to make sure timeDifference is in legal range 
                if (timeDifference > FilePersistenceService.MaxInterval)
{
timeDifference = FilePersistenceService.MaxInterval;
}
else if (timeDifference < TimeSpan.Zero)
{
timeDifference = TimeSpan.Zero;
}
this.instanceTimers.Add(contextGuid, new System.Threading.Timer(
callback,
subscription.WorkflowInstanceId,
timeDifference,
new TimeSpan(-1)));
}
}
private void ReloadWorkflow(object id)
{
// Reload the workflow so that it will continue processing 
            Timer toDispose;
if (this.instanceTimers.TryGetValue((Guid)id, out toDispose))
{
this.instanceTimers.Remove((Guid)id);
toDispose.Dispose();
}
this.Runtime.GetWorkflow((Guid)id);
}
// Load workflow instance state. 
        protected override Activity LoadWorkflowInstanceState(Guid instanceId)
{
Console.WriteLine("Loading instance: {0}\n", instanceId);
byte[] workflowBytes = DeserializeFromFile(instanceId);
return WorkflowPersistenceService.RestoreFromDefaultSerializedForm(workflowBytes, null);
}
// Unlock the workflow instance state.
// Instance state locking is necessary when multiple runtimes share instance persistence store 
        protected override void UnlockWorkflowInstanceState(Activity state)
{
//File locking is not supported in this sample 
        }
// Save the completed activity state. 
        protected override void SaveCompletedContextActivity(Activity activity)
{
Guid contextGuid = (Guid)activity.GetValue(Activity.ActivityContextGuidProperty);
Console.WriteLine("Saving completed activity context: {0}", contextGuid);
SerializeToFile(
WorkflowPersistenceService.GetDefaultSerializedForm(activity), contextGuid);
}
// Load the completed activity state. 
        protected override Activity LoadCompletedContextActivity(Guid activityId, Activity outerActivity)
{
Console.WriteLine("Loading completed activity context: {0}", activityId);
byte[] workflowBytes = DeserializeFromFile(activityId);
Activity deserializedActivities = WorkflowPersistenceService.RestoreFromDefaultSerializedForm(workflowBytes, outerActivity);
return deserializedActivities;
}
protected override bool UnloadOnIdle(Activity activity)
{
return unloadOnIdle;
}
// Serialize the activity instance state to file 
        private void SerializeToFile(byte[] workflowBytes, Guid id)
{
String filename = id.ToString();
FileStream fileStream = null;
try
{
if (File.Exists(filename))
File.Delete(filename);
fileStream = new FileStream(filename, FileMode.CreateNew, FileAccess.Write, FileShare.None);
// Get the serialized form 
                fileStream.Write(workflowBytes, 0, workflowBytes.Length);
}
finally
{
if (fileStream != null)
fileStream.Close();
}
}
// Deserialize the instance state from the file given the instance id 
        private byte[] DeserializeFromFile(Guid id)
{
String filename = id.ToString();
FileStream fileStream = null;
try
{
// File opened for shared reads but no writes by anyone 
                fileStream = new FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read);
fileStream.Seek(0, SeekOrigin.Begin);
byte[] workflowBytes = new byte[fileStream.Length];
// Get the serialized form 
                fileStream.Read(workflowBytes, 0, workflowBytes.Length);
return workflowBytes;
}
finally
{
fileStream.Close();
}
}
}