VSTHRD112.md

VSTHRD112 Implement System.IAsyncDisposable

The Microsoft.VisualStudio.Threading.IAsyncDisposable interface is obsolete now that the System.IAsyncDisposable interface has been defined for .NET Standard 2.0 and .NET Framework 4.6.1 by the Microsoft.Bcl.AsyncInterfaces NuGet package.

New classes looking to support async disposable should use System.IAsyncDisposable instead of Microsoft.VisualStudio.Threading.IAsyncDisposable. Existing classes that already implement Microsoft.VisualStudio.Threading.IAsyncDisposable should also implement System.IAsyncDisposable so the async disposal option will be recognized by code that only checks for presence of the new interface.

Examples of patterns that are flagged by this analyzer

This class only implements Microsoft.VisualStudio.Threading.IAsyncDisposable and will produce the VSTHRD112 diagnostic:

using Microsoft.VisualStudio.Threading;

class SomeClass : IAsyncDisposable
{
    public Task DisposeAsync()
    {
    }
}

Solution

Implement System.IAsyncDisposable in addition to (or instead of) Microsoft.VisualStudio.Threading.IAsyncDisposable. Add a package reference to Microsoft.Bcl.AsyncInterfaces if the compiler cannot find System.IAsyncDisposable.

In this example, only System.IAsyncDisposable is supported, which is acceptable:

using System;

class SomeClass : IAsyncDisposable
{
    public ValueTask DisposeAsync()
    {
    }
}

In this next example, both interfaces are supported:

class SomeClass : System.IAsyncDisposable, Microsoft.VisualStudio.Threading.IAsyncDisposable
{
    Task Microsoft.VisualStudio.Threading.IAsyncDisposable.DisposeAsync()
    {
        // Simply forward the call to the other DisposeAsync overload.
        System.IAsyncDisposable self = this;
        return self.Dispose().AsTask();
    }

    ValueTask System.IAsyncDisposable.DisposeAsync()
    {
        // Interesting dispose logic here.
    }
}

In the above example both DisposeAsync methods are explicit interface implementations. Promoting one of the methods to be public is typically advised. If one of these methods was already public and the class itself is public or protected, keep the same method public to avoid an API binary breaking change.

An automated code fix may be offered for VSTHRD112 diagnostics.