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Re: OS_GBPB 12 in a Wimp task

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In message <934f047152.Alan.Adams@laptop.adamshome.org.uk>
 on 15 Mar 2012 Alan Adams  wrote:

> In message <4c94017152.Matthew@sinenomine.freeserve.co.uk>
>           Matthew Phillips <spam2011m@yahoo.co.uk> wrote:
> 
> <snip>
> 
> > My inclination (from the filing system author's point of view) is that
> > there are quite a few weird and wonderful filing systems where it would
> > be pretty hard to treat R4 as a random access file index into the
> > directory.  But I appreciate that the application author doesn't always
> > have much option if the application is to multi-task and behave
> > responsively.  Perhaps we need a way of asking the filing system to go
> > backwards, as well as forwards?!  But that would involve a new API, which
> > would be even less likely to be achievable than the alternatives of
> > rewriting FileAction (and other apps) or rewriting the filing systems!
> 
> Aren't we missing something? RISC OS is a single-user operating 
> system. If the user chooses to modify a directory while the same user 
> is using the filer to copy to or from it, then they should expect 
> slightly odd behaviour.
> 
> It would of course be a slightly different matter if a background 
> process did the copy while the user was modifying things (backup?) or 
> modified things while the user copied (email arriving?)

The problem we have been discussing with FilerAction occurs, I think, during
Move or Delete operations.

Suppose you had selected a bunch of files in a directory, shift-dragged them
to move them elsewhere, and while that was proceeding, chose to delete
another file in the same directory.  The way FilerAction is implemented,
relying as it does on the unstated behaviour of FileCore filing systems,
means that on other filing systems unaware of this problem you might find
that the wrong files end up being moved.

You might find this irritating, especially if you then selected all the
remaining ones and deleted them without checking first.
 
> Why an application would need to go backwards I can't imagine, but 
> surely if it did, then it would either need to have counted the files 
> scanned so far, and rescan to the same number, or remember the name 
> and rescan.

That would be an alternative, but we are trying to avoid re-doing the
scanning: some contributors have pointed out that scanning directories can be
slow on some filing systems.

I mentioned going backwards because that's what FilerAction does, in effect
(see the rest of the thread).  After deleting or moving files from a
directory, FilerAction deducts the number of files processed so far from R4
before getting the next batch of filenames from OS_GBPB.  This is not
guaranteed to work with all filing systems out there because the requirement
that it be supported has never been spelled out to filing system developers.

> Either way, surely it's the application's responsibility -  the
> documentation says "pass back the value you received in R4". The only other
> valid value is 0 - start a new scan.

We'e all agreed what the documentation says: the trouble is FilerAction
abuses R4.  And going back to the original question, Chris was asking whether
it is considered safe to preserve and use the R4 value across Wimp_Polls.  In
the general case, it is not, but you might then end up with the desktop not
multi-tasking while an application deals with all 30,000 files in an
NFS-mounted directory across a 10Mb network (to give Steve's example).

I feel as though this thread is starting to go round in circles (like a hard
disc?!).

-- 
Matthew Phillips
Durham

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OS_GBPB 12 in a Wimp task Christopher Bazley <cs99cjb@gmail.com> - 2012-03-06 14:33 -0800
  Re: OS_GBPB 12 in a Wimp task jeff <jeffrey.a.doggett@gmail.com> - 2012-03-07 00:02 -0800
    Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-08 22:33 +0000
      Re: OS_GBPB 12 in a Wimp task Christopher Bazley <cs99cjb@gmail.com> - 2012-03-10 10:22 -0800
        Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-10 21:04 +0000
          Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-10 23:11 +0100
            Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-11 09:10 +0000
              Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-11 10:41 +0000
              Re: OS_GBPB 12 in a Wimp task Steve Fryatt <news@stevefryatt.org.uk> - 2012-03-11 11:06 +0000
              Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-11 17:56 +0100
                Re: OS_GBPB 12 in a Wimp task Gavin Wraith <gavin@wra1th.plus.com> - 2012-03-11 18:25 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-12 00:33 +0100
                Re: OS_GBPB 12 in a Wimp task Gavin Wraith <gavin@wra1th.plus.com> - 2012-03-12 11:56 +0000
                Re: OS_GBPB 12 in a Wimp task Martin Wuerthner <spamtrap@mw-software.com> - 2012-03-12 16:44 +0100
                Re: OS_GBPB 12 in a Wimp task druck <news@druck.org.uk> - 2012-03-12 20:57 +0000
                Re: OS_GBPB 12 in a Wimp task Martin Wuerthner <spamtrap@mw-software.com> - 2012-03-12 22:26 +0100
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-13 17:50 +0100
                Re: OS_GBPB 12 in a Wimp task jgharston <jgh@arcade.demon.co.uk> - 2012-03-13 10:15 -0700
                Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-13 07:34 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-14 06:00 +0100
                Re: OS_GBPB 12 in a Wimp task Christopher Bazley <cs99cjb@gmail.com> - 2012-03-15 02:40 -0700
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-15 14:55 +0100
                Re: OS_GBPB 12 in a Wimp task "Ste (news)" <steve@revi11.plus.com> - 2012-03-15 14:46 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-15 18:44 +0100
                Re: OS_GBPB 12 in a Wimp task Jeremy Nicoll - news posts <jn.nntp.scrap007@wingsandbeaks.org.uk> - 2012-03-15 19:44 +0000
                Re: OS_GBPB 12 in a Wimp task Alan Adams <alan@adamshome.org.uk> - 2012-03-15 20:36 +0000
                Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-15 20:26 +0000
                Re: OS_GBPB 12 in a Wimp task Rick Murray <heyrickmail-usenet@yahoo.co.uk> - 2012-03-16 06:12 +0100
                Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-15 20:34 +0000
                Re: OS_GBPB 12 in a Wimp task Alan Adams <alan@adamshome.org.uk> - 2012-03-15 21:04 +0000
                Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-16 00:17 +0000
        Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-10 23:58 +0000
          Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-11 10:43 +0000
          Re: OS_GBPB 12 in a Wimp task jeff <jeffrey.a.doggett@gmail.com> - 2012-03-12 03:03 -0700
            Re: OS_GBPB 12 in a Wimp task Chris Johnson <chrisjohnson+news@spamcop.net> - 2012-03-12 10:44 +0000
            Re: OS_GBPB 12 in a Wimp task Matthew Phillips <spam2011m@yahoo.co.uk> - 2012-03-13 07:44 +0000
              Re: OS_GBPB 12 in a Wimp task jeff <jeffrey.a.doggett@gmail.com> - 2012-03-13 03:06 -0700
  Re: OS_GBPB 12 in a Wimp task druck <news@druck.org.uk> - 2012-03-07 10:08 +0000

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