public delegate void WorkItemHandler<TItem>(
	TItem workItem
)
where TItem : WorkItem

WorkItemHandler<WorkItem> workItemHandler = 
    delegate(WorkItem workItem)
    {
        AnalysisServices.GetService<ApplicationThread>().InvokeAsynchronously(delegate()
        {
            try
            {
                if (workItem.IsResultValid && !workItem.IsCanceled)
                {
                    // do something to the document.
                }
            }
            finally
            {
                // Tell threading framework that your work item handler is done.
                workItem.ReturnItem();
            }

        });
     };