delphi - External exception C0000006

Question

I've wrote some program in Delphi and when I am running it from a disk on key. At some point I'm required to unplug the disk on key while the application is running. If I do this on a computer with at least 1gb of ram everything is okay. When I do this on a machine with 512mb I get an external exception C0000006. If I'm not mistaken, this is because the OS is trying to read the next line of code but cannot find the resource for it (meaning, the application wasn't loaded to the ram) which is absurd because it's a 500kb application.

How can I solve this? or at least handle this exception in a more elegant way? (Since I can't catch it since it's an external exception).

Oh, and my Delphi application is a console application under windows xp.

Answer 1

What you need to do is tell windows to load your whole program into memory, rather than allowing it to demand load pages when it needs to. I have done this successfully for applications running off a CD. I don't have the code with me right now, but I recall that I found hints on how to do it in source for the fantastic open source install program Inno Setup.

Edit: Actually, after doing a little research, you can use a Delphi compiler directive to tell windows to load the full executable. This works if you have Delphi > 2006. This will have the effect that you will never get the external exception.

Put this line in your applications project file:

{$SetPEFlags IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP}

This tells windows that the executable is going to be used from removable media, so load the the executable into memory (or the swap file). Then you don't need to worry about things like copying the file to the machine first, etc.

Edit 2: I currently have access to Delphi 7 and I can confirm, as noted by others, that this also works with Delphi 7 (and likely Delphi 6) with the following code:

const
  IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP = $0400;

{$SetPEFlags IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP}

For Delphi < 6, you can go down the path of forcing the executable to be paged in. There is an example of how to do it in C++ here (unless you find a way to modify the PE header flags after link time, which looks to be complicated)

N@