How to porting the wp8 app

1.  http://qedcode.com/content/awaitable-critical-section: 仅仅支持异步请求，并且不再支持thread的lock 方法，使用

using (var section = await _criticalSection.EnterAsync())代替了。

wp7:
   1: lock (this)
   2: {
   3:     FileHandle file = FileHandle.Open();
   4:     file.Write(value);
   5:     file.Close();
   6: }
wp8:
   1: using (var section = await _criticalSection.EnterAsync())
   2: {
   3:     FileHandle file = await FileHandle.OpenAsync();
   4:     await file.WriteAsync(value);
   5:     file.Close();
   6: }
2. http://www.hanselman.com/blog/UpdatingMyWindowsPhoneAppToWindowsPhone8.aspx