Windows Phone - Using a Mutex for Isolated Storage

Question

I am trying to protect my isolated storage using a mutex in order to access it both from a mobile application and from BackgroundAudioPlayer.

This is my class of helpers for accessing files in isostorage:

    public static async Task WriteToFile(string text)
    {
        using (var mut = new Mutex(false, "IsoStorageMutex"))
        {
            mut.WaitOne();
            try
            {
                // Get the text data from the textbox. 
                byte[] fileBytes = System.Text.Encoding.UTF8.GetBytes(text.ToCharArray());

                // Get the local folder.
                var local = ApplicationData.Current.LocalFolder;

                // Create a new folder name DataFolder.
                var dataFolder = await local.CreateFolderAsync("MusicFolder",
                                                               CreationCollisionOption.OpenIfExists);

                // Create a new file named DataFile.txt.
                var file = await dataFolder.CreateFileAsync("Streams.txt",
                                                            CreationCollisionOption.ReplaceExisting);

                // Write the data from the textbox.
                using (var s = await file.OpenStreamForWriteAsync())
                {
                    s.Write(fileBytes, 0, fileBytes.Length);
                }
            }
            finally
            {
                mut.ReleaseMutex();
            }
        }
    }

    public static async Task<string> ReadFile()
    {
        using (var mut = new Mutex(false, "IsoStorageMutex"))
        {
              mut.WaitOne();
              var result = String.Empty;
              try
              {
                  // Get the local folder.
                  var local = ApplicationData.Current.LocalFolder;

                  if (local != null)
                  {
                      // Get the DataFolder folder.
                      var dataFolder = await local.GetFolderAsync("MusicFolder");

                      // Get the file.
                      var file = await dataFolder.OpenStreamForReadAsync("Streams.txt");

                      // Read the data.

                      using (var streamReader = new StreamReader(file))
                      {
                          result = streamReader.ReadToEnd();
                      }
                  }
              }
              finally
              {
                  mut.ReleaseMutex();
              }
              return result;
        }
    }

But when I try to access it in the background agent, I get this error:

 Object synchronization method was called from an unsynchronized block of code.

Stacktrace:

   at System.Threading.Mutex.ReleaseMutex()
   at YouRadio.IsolatedStorage.StorageHelpers.<ReadFile>d__b.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at YouRadio.AudioPlaybackAgent.AudioPlayer.<AddTracksFromIsoStorageToPlaylist>d__6.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at YouRadio.AudioPlaybackAgent.AudioPlayer.<OnUserAction>d__2.MoveNext()

What am I doing wrong?

Answer 1

Mutex . , StorageHelper .

public class IsolatedStorageHelper
{
    private static Mutex mut = new Mutex(false, "IsoStorageMutex");

    public static async Task WriteToFile(string text)
    {
        mut.WaitOne();
        try
        {
            ...
        }
        finally
        {
            mut.ReleaseMutex();
        }
    }

    public static async Task<string> ReadFile()
    {
          mut.WaitOne();
          var result = String.Empty;
          try
          {
              ...
          }
          finally
          {
              mut.ReleaseMutex();
          }
          return result;
    }
}

-, - . , , , ReleaseMutex(). , .

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