Starting with C# 8.0, you can create and consume streams asynchronously. A method that returns an asynchronous stream has three properties:
- It's declared with the
asyncmodifier. - It returns an
System.Collections.Generic.IAsyncEnumerable<T> - The method contains
yield returnstatements to return successive elements in the asynchronous stream.
Consuming an asynchronous stream requires you to add the await keyword before the foreach keyword when you enumerate the elements of the stream. Adding the await keyword requires the method that enumerates the asynchronous stream to be declared with the async modifier and to return a type allowed for an async method. Typically that means returning a System.Threading.Tasks.Task or System.Threading.Tasks.Task<T>. It can also be a System.Threading.Tasks.ValueTask or System.Threading.Tasks.ValueTask<T>. A method can both consume and produce an asynchronous stream, which means it would return an System.Collections.Generic.IAsyncEnumerable<T>. The following code generates a sequence from 0 to 19. Every 3 elements, it pauses for 2 seconds to simulate retrieving the next set from a device:
You would enumerate the sequence using the await foreach statement:
Click the run button to experiment. Look at the times when elements are retrieved. Change some of the constants to experiment with different values, or time delays.
Note: This sandbox environment will timeout and halt programs that appear to be stuck. Avoid very long delays or very large sequences.