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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37
第 3 章
异步流
异步流
（
asynchronous stream
）是一种异步接收多个数据项的方式，其建立在异步枚举之
上（
IAsyncEnumerable<T>
）。异步枚举是一种异步版本的枚举，也就是说，它可以依照使
用者的要求异步生成数据项。
对比异步流与其他耳熟能详的类型，并思考它们之间的区别，这样做非常有用，可以帮助
我们理解何时应当使用异步流，何时其他类型更为适用。
3.1
异步流和
Task<T>
Task<T>
的标准异步方法只足以应对异步处理单个数据值。一旦某个
Task<T>
完成，任务就
结束了。单个
Task<T>
不能为其使用者提供多个
T
值。即使
T
是一个集合，该值也只能提
供一次。关于如何结合
Task<T>
与
async
，参见
1.2
节及第
2
章。
与
Task<T>
相比，异步流更类似于枚举。具体来说，
IAsyncEnumerator<T>
可以提供任意数量
的
T
值，而且一次一个。和
IEnumerator<T>
一样，
IAsyncEnumerator<T>
可以是无限长的。
3.2
异步流和
IEnumerable<T>
顾名思义，
IAsyncEnumerable<T>
与
IEnumerable<T>
相似。这或许并不奇怪，它们都能让使
用者以一次一个的方式获取元素。至于二者的差别，从名字上便能洞悉：一个是异步的，
而另一个不是。
当代码遍历
IEnumerable<T>
并从枚举获取每一个元素时，它会顺带阻塞。如果
IEnumerable<T>
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