AsyncEnumerator 1.5.0

Introduces IAsyncEnumerable, IAsyncEnumerator, ForEachAsync(), and ParallelForEachAsync()


Helps to (a) create an element provider, where producing an element can take a lot of time
due to dependency on other asynchronous events (e.g. wait handles, network streams), and
(b) a consumer that processes those element as soon as they are ready without blocking
the thread (the processing is scheduled on a worker thread instead).


using System.Collections.Async;

static IAsyncEnumerable<int> ProduceAsyncNumbers(int start, int end)
 return new AsyncEnumerable<int>(async yield => {

   // Just to show that ReturnAsync can be used multiple times
   await yield.ReturnAsync(start);

   for (int number = start + 1; number <= end; number++)
     await yield.ReturnAsync(number);

   // You can break the enumeration loop with the following call:

   // This won't be executed due to the loop break above
   await yield.ReturnAsync(12345);

// Just to compare with synchronous version of enumerator
static IEnumerable<int> ProduceNumbers(int start, int end)
 yield return start;

 for (int number = start + 1; number <= end; number++)
   yield return number;

 yield break;

 yield return 12345;

static async Task ConsumeNumbersAsync()
 var asyncEnumerableCollection = ProduceAsyncNumbers(start: 1, end: 10);
 await asyncEnumerableCollection.ForEachAsync(async number => {
   await Console.Out.WriteLineAsync($"{number}");

// Just to compare with synchronous version of enumeration
static void ConsumeNumbers()
 // NOTE: IAsyncEnumerable is derived from IEnumerable, so you can use either
 var enumerableCollection = ProduceAsyncNumbers(start: 1, end: 10);
 //var enumerableCollection = ProduceNumbers(start: 1, end: 10);

 foreach (var number in enumerableCollection) {

There is a newer version of this package available.
See the version list below for details.
Install-Package AsyncEnumerator -Version 1.5.0
dotnet add package AsyncEnumerator --version 1.5.0
<PackageReference Include="AsyncEnumerator" Version="1.5.0" />
For projects that support PackageReference, copy this XML node into the project file to reference the package.
paket add AsyncEnumerator --version 1.5.0
The NuGet Team does not provide support for this client. Please contact its maintainers for support.

Release Notes

1.5.0: Add support for .NET Standard, minor improvements.
1.4.2: Add finalizer to AsyncEnumerator and call Dispose in ForEachAsync and ParallelForEachAsync extension methods.
1.4.0: Add new generic type AsyncEnumeratorWithState for performance optimization.
      Now IAsyncEnumerator<T> is covariant.
      Add ForEachAsync, ParallelForeachAsync, and LINQ-style extension methods for IAsyncEnumerator.
1.3.0: Significantly improve performance of AsyncEnumerator by reducing thread switching and re-using instances of TaskCompletionSource.
      Add support for a state object that can be passed into AsyncEnumerable and AsyncEnumerator for performance optimization.
      Remove CancellationToken from Select/Take/Skip/Where extension methods - fix improper implementation.
      Move AsyncEnumerationCanceledException out of the generic AsyncEnumerator type.
      Change default behavior of the ToAsyncEnumerable extension method - now MoveNextAsync will run synchronously by default.
1.2.3: AsyncEnumerationCanceledException is thrown to the async enumeration function when the AsyncEnumerator is disposed before reaching the end of enumeration, what allows to do the clean-up.
      Fixed MoveNextAsync() that threw an exception sometimes only when you passed the end of enumeration.
1.2.2: Fix exception propagation in AsyncEnumerator.
1.2.1: New Linq-style extension methods in System.Collections.Async namespace.
1.2.0: Contract breaking changes in ParallelForEachAsync: introduce ParallelForEachException to unify error outcome of the loop.
1.1.0: Add ParallelForEachAsync extension methods for IEnumerable<T> and IAsyncEnumerable<T> in System.Collections.Async namespace.


This package has no dependencies.

Showing the top 3 GitHub repositories that depend on AsyncEnumerator:

Repository Stars
Distributed transaction solution in micro-service base on eventually consistency, also an eventbus with Outbox pattern
Open source utility to manage Steam, Origin and Uplay libraries in ease of use with multi library support
Blockchain core in C#/.NET for persistent peer-to-peer online games

Version History

Version Downloads Last updated
4.0.0 0 10/18/2019
3.1.0 4,851 9/23/2019
2.2.2 278,773 1/27/2019
2.2.1 399,744 5/29/2018
2.2.0 14,213 5/18/2018
2.1.1 82,410 1/20/2018
2.1.0 156,828 5/22/2017
2.0.1 43,191 2/13/2017
1.5.0 3,006 2/12/2017
1.4.2 1,022 2/6/2017
1.3.0 1,293 1/20/2017
1.2.3 6,338 1/6/2017
1.2.2 1,311 12/11/2016
1.2.1 373 12/10/2016
1.2.0 13,455 11/29/2016
1.1.3 392 11/28/2016
1.1.2 16,719 8/29/2016
1.0.3 1,867 4/28/2016
Show less