November 2020
Intermediate to advanced
226 pages
5h 34m
Chinese
Content preview from C#并发编程经典实例（第2版）
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38
｜
第
3
章
代表某些
I/O
密集型操作，比如数据库查询或
API
调用，那么消费者代码最终会阻塞
I/O
，
这并不理想。
IAsyncEnumerable<T>
的工作方式与
IEnumerable<T>
类似，但是它会异步获取
下一个元素。
3.3
异步流和
Task<IEnumerable<T>>
异步返回的集合完全可以包含多个数据项，
Task<List<T>>
就是一个常见的例子。返
回
List<T>
的
async
方法仍旧只有一条
return
语句，在将集合返回之前必须将其彻底填
充。即使是返回
Task<IEnumerable<T>>
的方法，也能够异步返回枚举，但随后该枚举将
被同步计算。注意，在
LINQ to Entities
中有一个
ToListAsync
LINQ
方法，该方法返回
Task<List<T>>
。当
LINQ
提供程序执行此操作时，它必须与数据库通信，并在完成填充列
表和返回它之前获取所有匹配的响应。
Task<IEnumerable<T>>
的局限在于无法返回刚获取的数据项。如果返回集合，那么它必
须把所有项都加载到内存中，填充该集合，然后一次性返回整个集合。即便它返回
LINQ
查询，并且可以异步构建该查询，但一经返回，该查询中的每一项也是同步获取的。
IAsyncEnumerable<T>
也会异步返回多个数据项，但区别在于，
IAsyncEnumerable<T>
可以
针对返回的每一项执行异步操作，这是真正由数据项组成的异步流。
3.4
异步流和
IObservable<T>
可观察对象是真正的异步流概念 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.