File in use: Cancel fails to rollbackSolved

We have a bug either in our software, or perhaps in Windows XP, or perhaps in my understanding of one of the most fundamental guarantees that Windows is supposed to offer (that all file handles are forcibly released when a process terminates).

Regardless of our bug, it highlights one of yours: when an error occurs during installing a patch, the user is only left with "cancel". If they cancel, then the patch is not rolled back. Their installation is left in a mixed state: part of the files are updated, and part are not.

I can see watching the wyUpdate status window that our files are being backed up... but then when you cancel, these backups are not restored. Why are they being backed up if not for the purpose of being able to recover (rollback) from a failed update?

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The error in question is ~ "File XXXX is in use. It must be closed in order to update it."