How to ensure saving of application state on crash c#

Question

I am very new to c# programming, so that in mind:

I have an in-memory data object with data I need to save the information when(if) my application were to crash OR closed. Is there a way to do this deterministically or reliably?

I have been looking at destructors

~MyObjectName(){}

finalizers and Dispose(),

but as far as I understand none of these will do reliably what I want?

Currently I am using the destructor, and it works when I am closing the program, but this doesn't mean it will work on crashing, or always.

Should I be looking at events as well?

Answer 1

There is no 100% reliable mechanism that you can use to save data (or do anything else for that matter) when a process (any process, not just a .Net process) terminates - most processes can be terminated at any point using the "End Process" option in the task manager, when this happens the process is immediately killed. As a more extreme example the power cord could be pulled out the back of the machine.

If its not 100% necessary that this data object be up-to-date and saved once the process is killed then the AppDomain.UnhandledException Event may suffice.

If its absolutely 100% necessary that this be the case then you need to be continuously saving this information as the process is running - there is absolutely no guarentee that you will get a chance to do it at a later date. This is how databases operate, no transaction returns until some record of the change has been recorded to disk in some format (eg a transaction log). This is what the D stands for in ACID .

Answer 2

I believe you are looking for catching unhandled exceptions? something like this:

static void Main()
{
  Application.EnableVisualStyles();
  Application.SetCompatibleTextRenderingDefault(false);

  Application.ThreadException += new ThreadExceptionEventHandler(Application_ThreadException);
  AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);

  Application.Run(new Form1());
}

static void Application_ThreadException(object sender, ThreadExceptionEventArgs e)
{
  MessageBox.Show(e.Exception.Message, "Unhandled Thread Exception");
  // here you can log the exception ...
}

static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
  MessageBox.Show((e.ExceptionObject as Exception).Message, "Unhandled UI Exception");
  // here you can log the exception ...
}

This example shows how to manage all exceptions that haven't been caught in the try-catch sections (in Windows Forms application).

The UnhandledException event handles uncaught exceptions thrown from the main UI thread. The ThreadException event handles uncaught exceptions thrown from non-UI threads.

Answer 3

You can achieve this with windbg.

1. Keep a breakpoint in zwterminateprocess method in windbg. This method will be called when your application exits.
2. when the breakpoint is reached , use !dumpheap -type MyObjectName to get the address of your object
3. Use !dumpobject "address of MyObjectName" to know the values inside the object