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There is a newer version of this package available.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.

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Version History

Version Downloads Last updated
4.0.1 7,152 10/22/2019
4.0.0 1,408 10/18/2019
3.1.0 10,579 9/23/2019
2.2.2 326,660 1/27/2019
2.2.1 505,021 5/29/2018
2.2.0 15,137 5/18/2018
2.1.1 85,285 1/20/2018
2.1.0 162,069 5/22/2017
2.0.1 43,580 2/13/2017
1.5.0 3,049 2/12/2017
1.4.2 1,027 2/6/2017
1.3.0 1,295 1/20/2017
1.2.3 6,341 1/6/2017
1.2.2 1,342 12/11/2016
1.2.1 376 12/10/2016
1.2.0 14,428 11/29/2016
1.1.3 395 11/28/2016
1.1.2 17,108 8/29/2016
1.0.3 2,086 4/28/2016
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