Gotchas

Async / Await Gotchas

Spot the bug:

    internal Task<DataFormat> TestAsync()
    {
        using (var stream = File.Open("test.dat", FileMode.Open, FileAccess.Read, FileShare.Read))
        {
            return StreamProcessingUtil.DoSomethingAsync(stream);
        }
    }

Oops! We actually need to await the method that gets passed the stream, as without an await, the closing of the using will be hit, disposing the stream before our method has a chance to start or finish what it wants to do.

Solution:

    internal async Task<DataFormat> TestAsync()
    {
        using (var stream = File.Open("test.dat", FileMode.Open, FileAccess.Read, FileShare.Read))
        {
            return await StreamProcessingUtil.DoSomethingAsync(stream);
        }
    }

ConfigureAwait

ConfigureAwait is used to manage the SynchronizationContext in async / await.

Recommendations

Use ConfigureAwait(false) in non-UI code (i.e. libraries, general purpose code). Ugly, yes, but this will help mitigate threading and deadlocking issues, while also improving performance.

ReSharper Support

ReSharper can help you with ConfigureAwait analysis by adding to your .editorconfig:

configure_await_analysis_mode = <library|ui>

Further Reading

• ConfigureAwait FAQ