1·For each remote service, GWT requires two interfaces on the client side: a remote service interface and a remote service async interface.
对于每个远程服务，GWT在客户端需要两个接口：一个远程服务接口和一个远程服务异步接口。
2·Pass session information to the async callback handler.
将会话信息传递到异步回调处理程序。
3·A simple utility class is created to easily get the instance of the async remote interface (lines 7-13 in Listing 8).
通过创建简单的实用程序类很容易获得异步远程接口的实例(清单8中的第7 - 13行)。
4·With.net 4.5 and the introduction of async, continuation style programming takes the forefront.
然而，有了。NET 4.5和其中引入的异步机制，顺序样式的编程就取而代之，占据主导地位。
5·As a consequence, Close takes a Timeout and has an async version (since it can block), and also Close can throw Exceptions.
因此，Close方法会接收一个Timeout参数，并包括一个异步版本(因为它可能阻塞线程)，而且Close还会抛出异常。