什麼是多線程的最佳方式？

Question

我的應用程序有點問題。 我有一個數據庫編輯器，當我嘗試更新數據庫文件時有時會掛起。並非每次，而是經常發生，並且每次在數據庫發生任何更改之前都會發生。我想這是因爲沒有使用多線程。儘管我最近纔開始學習編程，但即使閱讀了幾條多線程解釋之後，我仍然迷失了方向。有人可以向我解釋我應該如何在我的具體示例中實現它？

 
    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

問題是你正在UI線程中運行查詢。下面是使用BackgroundWorker,沉重啓發從this example，並使用Arguments的示例。這樣它將在單獨的線程中運行，並且不會鎖定GUI。

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

以及實現：

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 2

你只需要使用異步C＃代碼中等待的關鍵字，並最終會導致DB我已經修改了你的代碼異步調用：

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 3

你的問題的核心是，我們在調用阻塞UI線程（同步）數據庫調用。這會在您等待數據庫時阻塞您的UI線程，而不是保持良好的響應。

在一般情況下，由於這些是基於I/O的操作，因此應該能夠使它們自然異步，按照Lakhtey's answer。 但是，SQLite不支持實際的異步操作。 :(

因此，在這種情況下，最好的辦法是剛剛收官數據庫工作到後臺線程注意使用Task.Run遠遠優於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); 
}