Olaf Meeuwissen <olaf.meeuwissen at avasys.jp> wrote:
Hi,
> I have a frontend that calls sane_cancel() and throws an exception
> (and no plans to fix that any time real soon).
The problem with the "warming up" thing is that it is not an error,
it's a /transient/ *status* that clears itself up with time. So it's
wrong for an operation to FAIL because of this.
It's the kind of thing that should not be part of SANE_Status (bad
naming for that, btw, as we see), but should be treated on its own.
We should add a sane_status() call to the API to handle this kind of
things, so the call flow becomes:
sane_start()
sane_status()
-> warming up: tell the user the scanner is not ready, poll
sane_status() until it's ready (but don't busy loop)
-> OK: go ahead
sane_read()
And the better part is, we can make it an optional call and keep the
current behaviour for SANE 1.0 frontends, effectively enabling a
backward-compatible SANE 1.1 evolution of the standard.
Later we can make it mandatory in the call flow for SANE 2.0 - then
sane_read() can bomb out in SANE 2.0 with a "sorry, not ready" if the
scanner is not ready for whatever reason and the caller did not bother
to check beforehand (or did and things changed). sane_status() then
tells you what's up.
Other status returned by sane_status() could be things like: stand by,
lamp off, lamp on, ... the status could be a bitfield. sane_status()
could be called at any time between sane_open() and sane_close()
without ill effects.
Again, the whole problem with "warming up" is that it makes no sense
to have an operation fail because of that; it's wrong wrong wrong, no
matter how you put it it's still wrong wrong wrong.
A "paper jammed" error is a permanent error condition until the user
clears it up. There's no point in having the frontend wait for the
error to clear in this case, because it'll take time and the scanner
will probably be switched off for that and/or need a reinit
anyway. Bailing out is the right thing to do here.
I hope this clears things up, and I'd very much like to see that
implemented that way. It makes much more sense, it's much more useful
and extensible IMHO.
JB.
--
Julien BLACHE <http://www.jblache.org>
<jb at jblache.org> GPG KeyID 0xF5D65169
