在Windows Phone 7/8中多线程和访问本地数据库

Question

I have a local database.

And I have simple class for works with the local database.

public class DataBase
{

    public void Select()
    {
        try
        {
            //something select from the DB
        }
        finally
        {

        }
    }

    public void Insert()
    {
        try
        {
            //something insert to the DB
        }
        finally
        {

        }
    }

    public void Update()
    {
        try
        {
            //something update in the DB
        }
        finally
        {

        }
    }


    public void Remove()
    {
        try
        {
            //something remove from the DB
        }
        finally
        {

        }
    }
}

A have many queries to local database from a different threads. But I work with local database only through a class DataBase. I want to avoid a situation where the selected data, which at the moment are deleted or updated, etc. So, I want to lock the database, making it available to only one thread at a time. But I do not want it to be a weak point of the app in terms of performance. How best to proceed? What best suits to the local database in Windows Phone 7/8?

Update

I found this post about concurrent database access. Maybe I'm wrong, but I think that's what I need.

I rewrote the code, now I have something like this

public class CacheDataContext : DataContext
    {    
      public static string DBConnectionString = "Data Source=isostore:/Cache.sdf";

      public CacheDataContext(string connectionString) : base(connectionString) { }

      public static AutoResetEvent OperationOnDatabaseUsers = new AutoResetEvent(true);

      public static AutoResetEvent OperationOnDatabaseCities = new AutoResetEvent(true);

     public static AutoResetEvent OperationOnDatabaseVenues = new AutoResetEvent(true);


     public Table<Users> UsersItems;

     public Table<Cities> CitiesItems;

     public Table<Venues> VenuesItems;    

    }

I have three tables in the local database. Important moment that I don't have related tables.

So I have three inherited from the CacheDataContext , which implements logic of work with concrete table. Each context locked independently of the other contexts through AutoResetEvent.

  public class CacheDataContextUsers : CacheDataContext
 {
    public CacheDataContextUsers(string connectionString)  
        : base(connectionString) { }

    public void ClearUsers()
    {
             try
             {
                  OperationOnDatabaseUsers.WaitOne();
                   using (CacheDataContext context = new CacheDataContext(DBConnectionString))
                     {   
                        //remove all users from the local database
                        context.SubmitChanges();
                     }
             }
             finally
             {
                 OperationOnDatabaseUsers.Set();
             }
    }

    public void AddUser(User newUser)
    {
             try
             {
                  OperationOnDatabaseUsers.WaitOne();
                   using (CacheDataContext context = new CacheDataContext(DBConnectionString))
                     {   
                        //add user
                        context.SubmitChanges();
                     }
             }
             finally
             {
                 OperationOnDatabaseUsers.Set();
             }
    }

    //other operations

 }




 public class CacheDataContextVenues : CacheDataContext
 {
    public CacheDataContextVenues(string connectionString)  
        : base(connectionString) { }

    public void ClearVenues()
    {
             try
             {
                  OperationOnDatabaseVenues.WaitOne();
                   using (CacheDataContext context = new CacheDataContext(DBConnectionString))
                     {   
                        //remove all venues from the local database
                        context.SubmitChanges();
                     }
             }
             finally
             {
                 OperationOnDatabaseVenues.Set();
             }
    }

    public void AddVenue(Venue newVenue)
    {
             try
             {
                  OperationOnDatabaseVenues.WaitOne();
                   using (CacheDataContext context = new CacheDataContext(DBConnectionString))
                     {   
                        //add venue
                        context.SubmitChanges();
                     }
             }
             finally
             {
                 OperationOnDatabaseVenues.Set();
             }
    }

    //other operations

 }

Answer 1

I haven't worked with databases. Maybe you should use Dispatcher Invoke method to do something with your DB and UI, because when you work wih threads and UI it's necessary to use Dispatcher.

And talking about writing and reading the database - it can be done at same time, but if some data is still being written, and you are doing read - the data won't show up till writting is done.

"making it available to only one thread at a time"

Try using locks and await. But what you are trying to do - is to develop multi-thread program that won't work faster then 1 thread... =/

Answer 2

If you are refering to DataContext then its not thread safe and yes you need to add locks in order for it to be consistent. InvalidOperationException could be solved by using the UI thread (Deployment.Current.Dispatcher.BeginInvoke( ()=> {...} )) just for the db.SubmitChanges() method as Cheese noted.

Another DB solution, more general, would be SQLite . Unfortunately I have not tested it with a multi-threaded Windows Phone application yet and thus I cannot tell you for sure if it will suit you or not, even though it is supposed to be a thread safe database.