Silverlight:异步调用中的 WaitOne 同步未按预期运行

我正在尝试使用 ManualResetEvent 来阻止，直到执行回调，但从未到达回调，即使我尝试在另一个线程上运行回调也是如此。

waitHandle = new ManualResetEvent(false);
DataServiceQueryer<MyEntity> dataServiceQueryer = new DataServiceQueryer<MyEntity>(dsQuery.Expression);
ThreadPool.QueueUserWorkItem(new WaitCallback(stateInfo =>
{
    dataServiceQueryer.ExecuteQuery();
}));
// waits here forever
waitHandle.WaitOne();
public class DataServiceQueryer<T> 
{
    //field, properties
    public void ExecuteQuery()
    {
        // this block is definitely executed
        _asyncResult = _query.BeginExecute(new AsyncCallback(c =>
        {
            // this is never reached
            QueryOperationResponse<T> result = _query.EndExecute(c) as QueryOperationResponse<T>;
            MainPage.ListRecords = new ObservableCollection<T>(result) as ObservableCollectionEx<MyEntity>;
            MainPage.waitHandle.Set();
        }), _query);
        // neither is this!
        var test = _asyncResult.AsyncWaitHandle.WaitOne(0);
    }
}

有什么建议吗？ 我最困惑的是为什么_asycResult任务似乎从未发生过。 我正在使用带有EF4的Silverlight 4和devart Oracle dotConnect提供程序。