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WorkflowQueue Class

Represents a workflow queue.

Namespace:  System.Workflow.Runtime
Assembly:  System.Workflow.Runtime (in System.Workflow.Runtime.dll)

public class WorkflowQueue

Workflow queues are used to pass messages between a host or host services and activities in a workflow. Any activity can create a WorkflowQueue by calling WorkflowQueuingService.CreateWorkflowQueue, and a host, a service, or another activity can call Enqueue to add an item to that WorkflowQueue. You can subscribe to the QueueItemAvailable event to be notified when an item arrives on the WorkflowQueue. You can use Peek to examine an item at the beginning of the WorkflowQueue and Dequeue to remove an item from the WorkflowQueue. Each WorkflowQueue is associated with a WorkflowQueuingService that you can use to perform other management operations on the WorkflowQueue, such as deleting the queue. QueuingService exposes the WorkflowQueuingService associated with this WorkflowQueue.

The following code example demonstrates how you can create a WorkflowQueue by calling the WorkflowQueuingService.GetWorkflowQueue method. It also uses the Count property to determine whether any messages exist in the current queue. Finally, the code uses the Dequeue method to remove and return the first object in the queue.

This code example is part of the File Watcher Activity SDK Sample from the FileSystemEvent.cs file. For more information, see File System Watcher Activity.

private bool ProcessQueueItem(ActivityExecutionContext context)
    WorkflowQueuingService qService = context.GetService<WorkflowQueuingService>();
    if (!qService.Exists(this.QueueName))
        return false;

    WorkflowQueue queue = qService.GetWorkflowQueue(this.QueueName);

    // If the queue has messages, then process the first one 
    if (queue.Count == 0)
        return false;

    FileWatcherEventArgs e = (FileWatcherEventArgs)queue.Dequeue();

    // Raise the FileSystemEvent 
    base.RaiseGenericEvent<FileWatcherEventArgs>(FileSystemEvent.FileWatcherEventHandlerEvent, this, e);

    DoUnsubscribe(context, this);
    return true;


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0