如何立即完全停止应用程序并显示消息？

Question

When my application needs to make an emergency stop, I could call Halt or ExitProcess to terminate it immediately. This shouldn't happen quietly, though; the user needs to be shown a message. Therefore I looked to FatalAppExit but was surprised that it keeps everything (timers, threads) running until the user has closed the dialog.

I understand that showing a UI owned by the process requires the process to keep running. The UI does not need to be owned by my process, however. The dialog presented by FatalAppExit seems to be owned by Windows, even though it keeps the process running as well.

The main problem with FatalAppExit is that it's blocking—I want the dialog but not wait for confirmation—so I still can't terminate right after. To circumvent this, I'd have to start a thread that calls FatalAppExit , wait for a bit and then terminate the process. Not liking the race condition there.

I could also launch a process of my own to show the message, but I'd rather not if Windows can handle it.

Does Windows provide means to both terminate and show a friendly message at the same time? Any other suggestions to handle this as cleanly as possible?

Answer 1

As far as I know the only option here is to start an external process that displays the message and terminate immediately. You could write your own program for that purpose (which might be the easiest option) or you could start a batch file like this:

msg "%USERNAME%" %*

This sends a message to the given user (%USERNAME% is the currently logged on user) and uses all parameters passed to it as the actual message.

Personally I would write my own program, so I could write a log entry and do other stuff if it becomes necessary later.

Answer 2

You can have a global variable, such as

var ShutdownMessage: string;

When you need to terminate with an error, do:

ShutdownMessage := 'Error occured';
Application.Terminate;

and in the dpr file after Application.Run:

if ShutdownMessage <> '' then
  MessageBox(0, PChar(ShutdownMessage), 'Error', MB_OK or MB_ICONERROR);

Then the message will be shown after all forms closed and main loop exited.

Or, if that fails, you can try to raise an exception after Application.Run - it should be propagated to OS