public static async Task<T> ReadJsonExSafe<T>(String fileName)
        {
            if (String.IsNullOrEmpty(fileName)) return default(T);

            string mutexName = "dependantOnApp" + fileName;
            return await TaskEx.Run(() =>
            {
                using (var myMutex = new Mutex(false, mutexName))
                {
                    try
                    {
                        myMutex.WaitOne();
                        using (var store = IsolatedStorageFile.GetUserStoreForApplication())
                        using (var stream = new IsolatedStorageFileStream(fileName, FileMode.Open, store))
                        using (var sr = new StreamReader(stream))
                        using (var jr = new JsonTextReader(sr))
                            return (T)jsonSerializer.Deserialize(jr);
                    }
                    catch { throw new Exception("Exception"); }
                    finally { myMutex.ReleaseMutex(); }
                }
            });
        }

        public static async Task<bool> WriteJsonExSafe<T>(String fileName, T content)
        {
            if (String.IsNullOrEmpty(fileName))
                return false;

            string mutexName = "dependantOnApp" + fileName;

            return await TaskEx.Run(() =>
            {
                using (var myMutex = new Mutex(false, mutexName))
                {
                    try
                    {
                        myMutex.WaitOne();
                        using (var store = IsolatedStorageFile.GetUserStoreForApplication())
                        {
                            store.CreateFolderIfNecessary(fileName);
                            using (var stream = new IsolatedStorageFileStream(fileName, FileMode.Create, FileAccess.Write, store))
                            using (var sw = new StreamWriter(stream))
                            using (var jw = new JsonTextWriter(sw))
                                jsonSerializer.Serialize(jw, content);
                        }
                    }
                    catch { throw new Exception("Exception"); }
                    finally { myMutex.ReleaseMutex(); }

                    return true;
                }
            });
        }