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From:	"Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
To:	"David A. Cobb" <superbiskit AT home DOT com>, <cygwin-apps AT cygwin DOT com>
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Subject:	Re: Restructuring gettext
Date:	Sat, 5 Jan 2002 10:06:41 +1100
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----- Original Message -----
From: "David A. Cobb" <superbiskit AT home DOT com>
> > I've thought about suggesting the same thing but the problem with
that
> > scenario is that if you cancel an installation, then all sorts of
stuff
> > is uninstalled -- which probably isn't what you expected.
>
> Probably not.  But "cancel" at what point in the process?  It's *real*
> hard to program an installation procedure that's robust in the face of
a
> user clicking the "cancel" button in the middle.  Even the
> "professional" packages are likely to barf.

It's trivial to design. You treat an install like a series of
transactions. You make the transactions as small as you can while
satisfing all the system constraints - dependencies etc.

Once we've got per version dependencies and conflicts, and ordered
package actions (already described in this list) all we need to do is
make transactions that begin when a _current_ dependency/conflict is
being affected and finish when the system again has a consistent set of
dependencies and conflicts.

Additionally each package install/remove gets treated as an independent
transaction, to allow detection of in-use files.

Easy to code? Maybe not. Not too hard either. Replacing open files?
Sure. Already designed and proof-of-concept shown for setup.exe. How
many to queue at once? Until there are no in-process transactions.

The only restriction this puts on the setup process is that post install
scripts _must_ be able to be deferred until all the physical file
copying is complete.

Rob

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