AsyncDisposable Demo

Author: danielmarbach

.vscode/launch.json

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+{
+   // Use IntelliSense to find out which attributes exist for C# debugging
+   // Use hover for the description of the existing attributes
+   // For further information visit https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md
+   "version": "0.2.0",
+   "configurations": [
+        {
+            "name": ".NET Core Launch (console)",
+            "type": "coreclr",
+            "request": "launch",
+            "preLaunchTask": "build",
+            // If you have changed target frameworks, make sure to update the program path.
+            "program": "${workspaceFolder}/bin/Debug/netcoreapp3.0/Async.Netcore.dll",
+            "args": [],
+            "cwd": "${workspaceFolder}",
+            // For more information about the 'console' field, see https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md#console-terminal-window
+            "console": "internalConsole",
+            "stopAtEntry": false
+        },
+        {
+            "name": ".NET Core Attach",
+            "type": "coreclr",
+            "request": "attach",
+            "processId": "${command:pickProcess}"
+        }
+    ]
+}

.vscode/tasks.json

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+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "build",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "build",
+                "${workspaceFolder}/Async.Netcore.csproj"
+            ],
+            "problemMatcher": "$tsc"
+        },
+        {
+            "label": "publish",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "publish",
+                "${workspaceFolder}/Async.Netcore.csproj"
+            ],
+            "problemMatcher": "$tsc"
+        },
+        {
+            "label": "watch",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "watch",
+                "run",
+                "${workspaceFolder}/Async.Netcore.csproj"
+            ],
+            "problemMatcher": "$tsc"
+        }
+    ]
+}

Async.Netcore.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <LangVersion>8.0</LangVersion>
+  </PropertyGroup>
+
+</Project>

AsyncDisposable.cs

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+using System;
+using System.IO;
+using System.Threading.Tasks;
+
+class AsyncDisposable : IRunnable
+{
+    public async Task Run()
+    {
+        using (var wrong = new WrongDisposable())
+        {
+        }
+
+        await using (var correct = new CorrectDisposable())
+        {
+        }        
+    }
+
+    class WrongDisposable : BaseForAsyncDisposable, IDisposable
+    {
+        public void Dispose()
+        {
+            Log();
+
+            // sync over async anti-pattern
+            stream.FlushAsync().GetAwaiter().GetResult();
+            stream.Dispose();
+        }
+    }
+
+    class CorrectDisposable : BaseForAsyncDisposable, IAsyncDisposable, IDisposable
+    {
+        public async ValueTask DisposeAsync()
+        {
+            Log();
+
+            await stream.FlushAsync().ConfigureAwait(false);
+            stream.Dispose();
+            // or
+            await stream.DisposeAsync().ConfigureAwait(false);
+        }
+
+        public void Dispose()
+        {
+            Log();
+
+            stream.Flush();
+            stream.Dispose();
+        }
+    }
+}

AsyncDisposableExtensions.cs

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+using System;
+using System.IO;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Tasks;
+
+static class AsyncDisposableExtensions
+{
+    public static void Explain(this AsyncDisposable runnable, TextWriter writer)
+    {
+        writer.WriteLine(@"
+- `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
+");
+    }
+}
+
+class BaseForAsyncDisposable
+{
+    protected Stream stream;
+
+    protected BaseForAsyncDisposable()
+    {
+        stream = new FakeStream();
+    }
+
+    protected void Log([CallerMemberName] string member = null)
+    {
+        Console.WriteLine($"{GetType().Name}.{member}()");
+    }
+
+    class FakeStream : Stream
+    {
+        public override bool CanRead => throw new NotImplementedException();
+
+        public override bool CanSeek => throw new NotImplementedException();
+
+        public override bool CanWrite => throw new NotImplementedException();
+
+        public override long Length => throw new NotImplementedException();
+
+        public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
+
+        public override void Flush()
+        {
+            Thread.Sleep(1000);
+        }
+
+        public override async Task FlushAsync(System.Threading.CancellationToken cancellationToken)
+        {
+            await Task.Delay(1000);
+        }
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void SetLength(long value)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}

IRunnable.cs

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+using System.Threading.Tasks;
+
+interface IRunnable
+{
+    Task Run();
+}