Async enumerable sample

Author: danielmarbach

Async.Netcore.csproj

@@ -6,4 +6,10 @@
     <LangVersion>8.0</LangVersion>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Update="AsyncEnumerable.txt">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
 </Project>

AsyncDisposable.cs

@@ -10,7 +10,8 @@ public async Task Run()
         {
         }
 
-        await using (var correct = new CorrectDisposable())
+        await using (var correct = new CorrectDisposable()
+            .ConfigureAwait(false))
         {
         }        
     }

AsyncEnumerable.cs

@@ -0,0 +1,43 @@
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Tasks;
+
+class AsyncEnumerable : IRunnable
+{
+    public async Task Run()
+    {
+        using var tokenSource = new CancellationTokenSource();
+        tokenSource.CancelAfter(3200);
+        
+        await foreach (var delay in ReadDelays()
+            .WithCancellation(tokenSource.Token)
+            .ConfigureAwait(false))
+        {
+            Console.WriteLine($"await Task.Delay({delay})");
+
+            await Task.Delay(delay)
+                .ConfigureAwait(false);
+        }
+    }
+
+    async IAsyncEnumerable<int> ReadDelays([EnumeratorCancellation] CancellationToken token = default)
+    {
+        using (var stream = File.OpenRead("AsyncEnumerable.txt"))
+        using (var reader = new StreamReader(stream))
+        {
+            string line;
+            while ((line = await reader.ReadLineAsync()
+                .ConfigureAwait(false)) != null)
+            {
+                token.ThrowIfCancellationRequested();
+                Console.WriteLine("  Read next line");
+                yield return Convert.ToInt32(line);
+            }
+        }
+        Console.WriteLine("  Done enumerating");
+    }
+}

AsyncEnumerable.txt

@@ -0,0 +1,7 @@
+100
+200
+400
+800
+1600
+3200
+6400

AsyncEnumerableExtensions.cs

@@ -0,0 +1,13 @@
+using System.IO;
+
+static class AsyncEnumerableExtensions
+{
+    public static void Explain(this AsyncEnumerable runnable, TextWriter writer)
+    {
+        writer.WriteLine(@"
+- `IAsyncEnumerable<T>` allows to write asynchronous pull based streams, similar to regular enumerables with `yield return` and `yield break`
+- `WithCancellation` only adds the token to the enumerator but doesn't influence the state machine
+- `WithCancellation` in combination with `[EnumeratorCancellation]` can be used to ceate a combined token
+");
+    }
+}

README.md

@@ -4,3 +4,9 @@
 - `Stream`, `BinaryWriter`, `TextWriter`  calls `.Dispose` synchronously
 - `Stream` `FlushAsync` calls `Flush` on another thread which is bad behavior that should be overwritten
 
+## AsyncEnumerable
+
+- `Stream`, `Utf8JsonWriter`, `System.Threading.Timer`, `CancellationTokenRegistration`, `BinaryWriter`, `TextWriter` and `IAsyncEnumerator<T>` implement `IAsyncDisposable`
+- `Stream`, `BinaryWriter`, `TextWriter`  calls `.Dispose` synchronously
+- `Stream` `FlushAsync` calls `Flush` on another thread which is bad behavior that should be overwritten
+