Question

I’m attempting to write to a file but “occasionally” I run into issues that I think are down to concurrency, as some of the time, I’m getting a System.UnauthorizedAccessException with message:

Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))

…from the following:

public async void SubmitChanges()
{
    DataContractSerializer serializer = 
        new DataContractSerializer(typeof(LocalCache<T>));

    StorageFile file = await ApplicationData.Current.LocalFolder
            .CreateFileAsync(GetFileNameForType(), 
                CreationCollisionOption.ReplaceExisting);

    //Occasionally throws here
    using (var fi = await file.OpenTransactedWriteAsync())
    {
        serializer.WriteObject(fi.Stream.AsStreamForWrite(), this);
        await fi.CommitAsync();
    }
}

I can only assume that this is down to some concurrency, or it being still open for read somewhere else, but I can’t seem to find a way to wait for it to become available – I’d normally lock around it, but this is not allowed with await so what are the other options?

Answer 1

Usually, you just don’t start the next operation until the previous operation is complete.

Tip: avoid async void; use async Task instead. That enables you to know when the previous operation is complete.