Windows Phone 8–Parallel async access fixed

Yesterday I have changed my file IO operations from IsolatedStorage (Windows Phone 7) to Windows.Storage classes (WinRT API for Windows Phone 8). One problem with the asynchronous call is that there could now be parallel calls to the same resource (in this case a file). With async methods you cannot use the common lock mechanism :-(

But my colleague Matthias (@JauMatt) has already found in the web a very nice solution for that: http://qedcode.com/content/awaitable-critical-section

My new code which using the class AwaitableCriticalSection looks than like this and works properly for Windows Phone 8, too:

        public static async Task SaveList<T>(string folderName, string dataName, List<T> dataList) where T : class

        {

            StorageFolder applicationFolder = ApplicationData.Current.LocalFolder;

            if (!await applicationFolder.FolderExistsAsync(folderName))

            {

                applicationFolder.CreateFolderAsync(dataName);

            }

            string fileStreamName = string.Format("{0}\\{1}.dat", folderName, dataName);

            using (var section = await CriticalSection.EnterAsync())

            {

                StorageFile file =

                    await

                    applicationFolder.CreateFileAsync(fileStreamName, CreationCollisionOption.ReplaceExisting);

                using (IRandomAccessStream randomAccessStream = await file.OpenAsync(FileAccessMode.ReadWrite))

                {

                    using (IOutputStream outStream = randomAccessStream.GetOutputStreamAt(0))

                    {

                        var serializer = new DataContractSerializer(typeof (List<T>));

                        serializer.WriteObject(outStream.AsStreamForWrite(), dataList);

                        await outStream.FlushAsync();

                    }

                }

            }

        }