MA0042.md

MA0042 - Do not use blocking calls in an async method

You should replace blocking calls, such as Wait or Result, with an async call using await.

public async Task Sample()
{
    Thread.Sleep(1); // Non compliant
    Task.Delay(1).Wait(); // non compliant
    await Task.Delay(1); // compliant

    var result = Task.Run(() => 10).Result; // non compliant
    var result = await Task.Run(() => 10); // compliant
}

The rule only reports a diagnostic when the enclosing method is already async or when the async keyword can be added with changing the return type. While you can use async void, the rule will not report a diagnostic when the method returns void. MA0045 detects the same cases, but reports them even if applying a fix would require you to change the calling method's signature.

public Task Sample()
{
    Thread.Sleep(1); // Non compliant, as you can add "async" to the signature without changing the return type
}

public int Sample()
{
    Thread.Sleep(1); // compliant, as you cannot add "async" to the signature without changing the return type
    return 0;
}

Additional resources

• Enforcing asynchronous code good practices using a Roslyn analyzer