这是如何导致无限循环的?

时间:2014-05-02 20:53:54

标签: c# infinite-loop messagebox visual-studio-debugging mutual-recursion

我坚持维护的一些遗留代码陷入无限循环(因此我自己似乎在一个);我不知道为什么/怎么样。

这是应用程序的入口点,它实例化主窗体(frmCentral):

CODE EXHIBIT A

public static int Main(string [] args)
{
    try
    {
        AppDomain currentDomain = AppDomain.CurrentDomain;

        currentDomain.UnhandledException += new UnhandledExceptionEventHandler(GlobalExceptionHandler);

        string name = Assembly.GetExecutingAssembly().GetName().Name;
        MessageBox.Show(string.Format("Executing assembly is {0}", name)); // TODO: Remove after testing <= this one is seen
        IntPtr mutexHandle = CreateMutex(IntPtr.Zero, true, name);
        long error = GetLastError();
        MessageBox.Show(string.Format("Last error int was {0}", error.ToString())); // TODO: Remove after testing <= this one is also seen

        if (error == ERROR_ALREADY_EXISTS)
        {
            ReleaseMutex(mutexHandle);

            IntPtr hWnd = FindWindow("#NETCF_AGL_BASE_", null);
            if ((int) hWnd > 0)
            {
                SetForegroundWindow(hWnd);  
            }
            return 0;
        }

        MessageBox.Show("made it into Main method #4"); // TODO: Remove after testing <= this one is seen

        ReleaseMutex(mutexHandle);

        MessageBox.Show("made it into Main method #5"); // TODO: Remove after testing <= this one is seen

        DeviceInfo devIn = DeviceInfo.GetInstance();

        MessageBox.Show("made it into Main method #6"); // TODO: Remove after testing <= this one is seen

        Wifi.DisableWifi();

        MessageBox.Show("made it into Main method #7"); // TODO: Remove after testing <= this one is seen

        // Instantiate a new instance of Form1.
        frmCentral f1 = new frmCentral();
        f1.Height = devIn.GetScreenHeight();
        f1.Text = SSCS.GetFormTitle("SSCS HHS", "", "");

        MessageBox.Show("made it before Application.Run() in Main method"); // TODO: Remove after testing <= this one is NOT seen
        Application.Run(f1);

        devIn.Close();

        Application.Exit();
        return 0;
    }
    catch(Exception ex)
    {
        SSCS.ExceptionHandler(ex, "Main");
        return 0;
    }
} // Main() method

frmCentral的构造函数然后调用一个名为 DBConnection.GetInstance()的单例方法(与glorified相反的是什么?):

CODE EXHIBIT B

public frmCentral()
{
    try
    {
        //
        // Required for Windows Form Designer support
        //
        InitializeComponent();
        MessageBox.Show("made it past InitializeComponent() in frmCentral constructor"); // <= this displays
        devIn = DeviceInfo.GetInstance();
        MessageBox.Show("made it past DeviceInfo.GetInstance() in frmCentral constructor"); // <= this displays
        dbconn = DBConnection.GetInstance();
        MessageBox.Show("made it past DBConnection.GetInstance() in frmCentral constructor");
        WindowState = FormWindowState.Maximized;

        UpdateMenuItemSelectable = false;
        ResetConnectionFetchForm = false;

        AllowNewItems = true;

        listboxWork.Focus();
        MessageBox.Show("made it through frmCentral constructor"); // <= this one does NOT display
    }
    catch (Exception ex)
    {
        SSCS.ExceptionHandler(ex, "frmCentral()");
    }
} // frmCentral Constructor

这是“光荣的”单一/种类的单身方法:

CODE EXHIBIT C

// Singleton pattern, or at least a derivation thereof
public static DBConnection GetInstance()
{
    MessageBox.Show("made it into DBConnection.GetInstance()");
    try
    {
        if (instance == null)
        {
            MessageBox.Show("made it into DBConnection.GetInstance(); instance was null");
            instance = new DBConnection();
        }
    }
    catch(Exception ex)
    {
        SSCS.ExceptionHandler(ex, "DBConnection.GetInstance");
    }
    return instance;
}

实例化DBConnection,因此调用其构造函数:

CODE EXHIBIT D

private DBConnection()
{
    try
    {
        // Connection String
        string conStr = "Data Source = " + filename;
        string cmpStr = conStr + ".tmp";
        MessageBox.Show(string.Format("made it into DBConnection constructor. cmpStr == {0}", cmpStr)); // TODO: Comment out or remove
        if (File.Exists(filename+".tmp"))
            File.Delete(filename+".tmp");

        engine = new SqlCeEngine(conStr);
        MessageBox.Show(string.Format("SqlCeEngine created. conStr == {0}", conStr)); // TODO: Comment out or remove

        if (File.Exists(filename))
        {
            MessageBox.Show(string.Format("file {0} exists", filename)); // TODO: Comment out or remove
        }
        else
        {
            // Create the SQL Server CE database
            engine.CreateDatabase();
            MessageBox.Show("Made it past call to engine.CreateDatabase()"); // TODO: Comment out or remove
        }
        engine.Dispose();

        objCon = new SqlCeConnection(conStr);
        MessageBox.Show("Made it past call to new SqlCeConnection(conStr)"); // TODO: Comment out or remove

        objCon.Open();
    }
    catch(Exception ex)
    {
        SSCS.ExceptionHandler(ex, "DBConnection.DBConnection");
    }
}

我从Code Exhibit A中看到* MessageBox.Show()* s(除非另有说明),然后代码图表B,然后是Code Exhibit C,然后是Code Exhibit D,然后它在C之间来回传递和D“直到奶牛回家。”

我不明白为什么DBConnection构造函数和DBConnection GetInstance()以递归方式相互调用,但是...我在大海捞针中是否有针,或是隐藏在普通视线中的大象,或者...... ???

更新

public static void ExceptionHandler(Exception ex, string location)
{
    try
    {
        MessageBox.Show("Exception: " + ex.Message + "\n\nLocation: " + location, GetFormTitle("SSCS: " + ex.GetType().FullName,"",""));
    }
    catch(Exception exc)
    {
        MessageBox.Show("Exception Handler generated an exception!\n" + exc.Message + "\n\nCalling Location: " + location, GetFormTitle("SSCS: " + exc.GetType().FullName,"",""));
    }
}

更新2

这是更有启发性的晦涩:

public static string GetFormTitle(string formName, string serialNo, string siteNo)
{

    string titleBar = formName == "" ? "SSCS HHS" : formName;

    if((serialNo == ""))
    {
        User person = new User();
        person.getUserFromTable();
        serialNo = person.getSerialNo();
    }

    if (frmCentral.HashSiteMapping.ContainsKey(siteNo))
    {
        siteNo = (string) frmCentral.HashSiteMapping[siteNo];
    }


    if (serialNo != "")
        titleBar += " - " + serialNo + (siteNo == "" ? "" : " Site #" + siteNo);

    return titleBar;
}

更新3

我添加的未捕获的异常代码:

currentDomain.UnhandledException += new UnhandledExceptionEventHandler(GlobalExceptionHandler);

static void GlobalExceptionHandler(object sender, UnhandledExceptionEventArgs args)
{
    Exception e = (Exception)args.ExceptionObject;
    MessageBox.Show(string.Format("GlobalExceptionHandler caught {0}; Compact Framework Version == {1}", e.Message, Environment.Version.ToString()));
}

我还没有看到任何证据表明此处理程序已经到达(无论如何,到目前为止)。

更新4

非常有趣 - 将一个MessageBox.Show(或两个)添加到GetFormTitle:

public static string GetFormTitle(string formName, string serialNo, string siteNo)
{
    MessageBox.Show(string.Format("GetFormTitle() reached. formName == {0}; serialNo == {1}; siteNo == {2}", formName, serialNo, siteNo)); // TODO: Remove after testing
    string titleBar = formName == "" ? "SSCS HHS" : formName;

    if((serialNo == ""))
    {
        User person = new User();
        person.getUserFromTable();
        serialNo = person.getSerialNo();
    }

    if (frmCentral.HashSiteMapping.ContainsKey(siteNo))
    {
        siteNo = (string) frmCentral.HashSiteMapping[siteNo];
    }


    if (serialNo != "")
        titleBar += " - " + serialNo + (siteNo == "" ? "" : " Site #" + siteNo);
    MessageBox.Show(string.Format("titleBar val about to be returned. Val is {0}", titleBar)); // TODO: Remove after testing
    return titleBar;
}

...这些是我现在看到的MessageBox.Show()的序列:

0) Made it into DBConnection.GetInstance() 
1) Made it into DBConnection.GetInstance() instance was null
2) Made it to DBConnection constructor cmpStr == ....
3) Sqlceengine created. conStr == ...
4) File \My Documents\HHSDB.SDF exists
5) Made it past call to new SqlCeConnection(conStr)
6) GetFormTitle() reached. fromName == SSCS:
System.Data.SqlserverCe.SqlCeException; serial No ==; siteNo ==

...接下来是一轮追尾,递归的消息,直到我热身启动(我讨厌反对Fab 4,但与流行的观点相反,幸福绝对不是热情的启动!*)

...就在MessageBox消息显示中,插入了一个异常!全宾夕法尼亚嘻哈(Key Rap)!

* Let's have no attempts at humor revolving around warm booty, now!

这是远程桌面调试的最佳展示,LB2!

1 个答案:

答案 0 :(得分:6)

以下是可能发生的事情(此时理论是OP可以确认的)

引发问题的事情......

在图表D中,启动无限循环链的问题可能是objCon.Open();。连接到数据库可能存在一些问题,Open()调用应该抛出异常。这当然会被紧跟在该行之后的本地catch中捕获。

更新1中显示的本地catch调用SSCS.ExceptionHandler。它看起来很温和,但在其中隐藏了罪魁祸首的帮凶,名称为GetFormTitle,显示在更新2.

事情变得更糟......

GetFormTitle有一段非常有趣的代码:

User person = new User();
person.getUserFromTable();

...最有可能是从数据库中检索用户信息的模型(其他地方)。

因此创建了无限循环......

好吧,要从数据库中获取User,需要一个连接,这很可能会导致调用DBConnection.GetInstance(),这会导致objCon.Open();开始新的循环,因此创建infinite loop(巧妙地,不使用任何语言的内置循环机制,需要及时注明)。

确认:

OP:请在GetFormTitle中放置非常简单的(意味着不要拨打GetFormTitle MessageBoxes),如果上述理论是正确的,那么你就是&#39;我会在执行的路径中看到它。