什么是多线程的最佳方式？

Question

I've got a little problem with my application. I have a database editor that hangs up sometimes when I try to update the database file. Not every time, but pretty often, and every time it happens right before any changes are made to the database. I figured it's because of not using multithreading. I've only started learning programming recently though, and I'm kind of lost even after reading through a few multithreading explanations. Could someone explain to me how should I implement it in my specific example?

private void adjustStatsButton_Click(object sender, EventArgs e)
    {
            ReadWrite.AdjustStats(winnerInput.Text, loserInput.Text);
            winnerInput.Text = "";
            loserInput.Text = "";
            Refresh(leaderboardBox);
    }

public class ReadWrite
    {
        public static void AdjustStats(string winner, string loser)
        {
            SQLiteConnection dbConnection = new SQLiteConnection("Data Source = Leaderboards.sqlite; Version = 3");


        string sql = "SELECT * FROM leaderboard WHERE name='" + winner + "'";
        SQLiteCommand command = new SQLiteCommand(sql, dbConnection);
        dbConnection.Open();
        SQLiteDataReader reader = command.ExecuteReader();


        double wrating = Convert.ToDouble(reader["rating"]);
        int wmatches = Convert.ToInt32(reader["matches"]);
        int wwins = Convert.ToInt32(reader["wins"]);

        sql = "SELECT * FROM leaderboard WHERE name='" + loser + "'";
        command = new SQLiteCommand(sql, dbConnection);
        reader = command.ExecuteReader();

        double lrating = Convert.ToDouble(reader["rating"]);
        int lmatches = Convert.ToInt32(reader["matches"]);
        int lwins = Convert.ToInt32(reader["wins"]);
        int llosses = Convert.ToInt32(reader["losses"]);

        double RC = (1 - ((wrating - lrating) / 200)) * 8;
        if (RC < 0) RC *= -1;
        if (RC < 4) RC = 4;
        else if (RC > 12) RC = 12;

        wmatches++;
        wwins++;
        lmatches++;
        llosses++;
        wrating += RC;
        if (wrating < 0) wrating = 0;
        lrating -= RC;
        if (lrating < 0) lrating = 0;
        double wwinrate = Convert.ToDouble(wwins) / wmatches;
        double lwinrate = Convert.ToDouble(lwins) / lmatches;

        sql = "UPDATE leaderboard SET rating=" + wrating + ", matches=" + wmatches + ", wins=" + wwins + ", winrate=" + wwinrate + " WHERE name='" + winner + "'";
        command = new SQLiteCommand(sql, dbConnection);
        command.ExecuteNonQuery();

        sql = "UPDATE leaderboard SET rating=" + lrating + ", matches=" + lmatches + ", losses=" + llosses + ", winrate=" + lwinrate + " WHERE name='" + loser + "'";
        command = new SQLiteCommand(sql, dbConnection);
        command.ExecuteNonQuery();
        dbConnection.Close();
        }
    }

Answer 1

You just need to use async await keywords within your c# code and it will eventually lead Asynchronous calls to the DB I have made changes to your Code :

private async void adjustStatsButton_Click(object sender, EventArgs e)
    {
            await ReadWrite.AdjustStats(winnerInput.Text, loserInput.Text);
            winnerInput.Text = "";
            loserInput.Text = "";
            Refresh(leaderboardBox);
    }


    public class ReadWrite
        {
            public static Task AdjustStats(string winner, string loser)
            {
    return Task.Run(() => 
    {
       SQLiteConnection dbConnection = new SQLiteConnection("Data Source = Leaderboards.sqlite; Version = 3");


            string sql = "SELECT * FROM leaderboard WHERE name='" + winner + "'";
            SQLiteCommand command = new SQLiteCommand(sql, dbConnection);
            dbConnection.Open();
            SQLiteDataReader reader = await command.ExecuteReaderAsync();


            double wrating = Convert.ToDouble(reader["rating"]);
            int wmatches = Convert.ToInt32(reader["matches"]);
            int wwins = Convert.ToInt32(reader["wins"]);

            sql = "SELECT * FROM leaderboard WHERE name='" + loser + "'";
            command = new SQLiteCommand(sql, dbConnection);
            reader = await command.ExecuteReaderAsync();

            double lrating = Convert.ToDouble(reader["rating"]);
            int lmatches = Convert.ToInt32(reader["matches"]);
            int lwins = Convert.ToInt32(reader["wins"]);
            int llosses = Convert.ToInt32(reader["losses"]);

            double RC = (1 - ((wrating - lrating) / 200)) * 8;
            if (RC < 0) RC *= -1;
            if (RC < 4) RC = 4;
            else if (RC > 12) RC = 12;

            wmatches++;
            wwins++;
            lmatches++;
            llosses++;
            wrating += RC;
            if (wrating < 0) wrating = 0;
            lrating -= RC;
            if (lrating < 0) lrating = 0;
            double wwinrate = Convert.ToDouble(wwins) / wmatches;
            double lwinrate = Convert.ToDouble(lwins) / lmatches;

            sql = "UPDATE leaderboard SET rating=" + wrating + ", matches=" + wmatches + ", wins=" + wwins + ", winrate=" + wwinrate + " WHERE name='" + winner + "'";
            command = new SQLiteCommand(sql, dbConnection);
            await command.ExecuteNonQueryAsync();

            sql = "UPDATE leaderboard SET rating=" + lrating + ", matches=" + lmatches + ", losses=" + llosses + ", winrate=" + lwinrate + " WHERE name='" + loser + "'";
            command = new SQLiteCommand(sql, dbConnection);
            await command.ExecuteNonQueryAsync();
            dbConnection.Close();
            }
});

        }

Answer 2

The problem is that you are running the query in the UI thread. Here's an example for using the BackgroundWorker , heavily inspired from this example , and using Arguments . This way it will be running in a separate thread and it will not lock the GUI.

// Class for passing arguments
public class BqArguments
{
    public string Winner {get;set}
    public string Loser {get;set}
}

And your implementation:

BackgroundWorker _bw; // You need to initialize this somewhere.

private void adjustStatsButton_Click(object sender, EventArgs e)
{
    // Maybe this should be initialized in ctor. But for this example we do it here...
    _bw = new BackgroundWorker();
    var arguments = new BqArguments
    {
       Winner = winnerInput.Text,
       Loser = loserInput.Text
    }
    _bw.DoWork += bw_DoWork;
    _bw.RunWorkerCompleted += bw_RunWorkerCompleted;
    _bw.RunWorkerAsync(arguments);    
}

private void bw_DoWork (object sender, DoWorkEventArgs e)
{
    // Run your query in the background.
    var arguments = e.Argument as BqArguments;
    ReadWrite.AdjustStats(arguments.Winner, arguments.Loser);
}

private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // All done. Let's update the GUI.
    winnerInput.Text = "";
    loserInput.Text = "";
    Refresh(leaderboardBox);
}

Answer 3

The core of your problem is that you're calling blocking (synchronous) database calls on the UI thread. This blocks your UI thread while it's waiting for the database, instead of keeping it nicely responsive.

In the general case, since these are I/O-based operations, you should be able to make them naturally asynchronous, as per Lakhtey's answer . However , SQLite does not support actual asynchronous operations. :(

So, in this case, your best bet is to just wrap up the database work into a background thread. Note that using Task.Run is far superior to BackgroundWorker :

private async void adjustStatsButton_Click(object sender, EventArgs e)
{
  await Task.Run(() => ReadWrite.AdjustStats(winnerInput.Text, loserInput.Text));
  winnerInput.Text = "";
  loserInput.Text = "";
  Refresh(leaderboardBox);
}