[sane-devel] Interactive use of scanner buttons

[Wilhelm Meier]

There is this old project of mine called "scanbd", the "scanner button
daemon". There wasn't low / no activity in the last year(s), but it is
still functional because it is strictly POSIX conform.

If anyone is interested in taking care of that, I would be very happy.

https://sourceforge.net/projects/scanbd/

Regards,
 Wilhelm

On 03.12.21 15:15, Kelly Price wrote:
> Well, that and if the access to the scanner is locked at the saned
> level, polling isn't going to tie it up and saned can always return a
> "We're busy scanning" signal.
> 
> On Fri, Dec 3, 2021 at 9:03 AM m. allan noah <kitno455 at gmail.com> wrote:
>>
>> Many backends are single threaded currently, so this would be a pretty invasive change. Frankly, polling over the network once per second is not that much traffic, and certainly easier to implement.
>>
>> allan
>>
>> On Fri, Dec 3, 2021 at 8:50 AM Paul Wolneykien <manowar at altlinux.org> wrote:
>>>
>>> В Thu, 2 Dec 2021 17:29:13 -0800
>>> Ralph Little <skelband at gmail.com> пишет:
>>>
>>>> However, regular polling can be
>>>> detrimental as a general feature. One commentator suggested that over
>>>> a network, this could become an unnecessary bandwidth hog. In SANE we
>>>> would want to add polling features in a generic fashion and we should
>>>> wary of undesirable side-effects. Flooding a network just because you
>>>> are sitting in an idle instance of xsane is certainly such an
>>>> example. It is something that we should discuss carefully before
>>>> enhancing the standard.
>>>
>>>   Yes, polling over the network is a very bad idea. That means, we need
>>> something like subscribe+notify interface in SANE. What about the
>>> following API upgrade?
>>>
>>>   A new capability for dynamic options (not only the buttons, but all
>>> things that could be changed by the scanner inself):
>>>
>>>   +  #define SANE_CAP_DYNAMIC
>>>
>>>   Then a new action for sane_control_option() indicating we want to
>>> subscribe to scanner-initiated updates of the given value:
>>>
>>>   + SANE_ACTION_SUBSCRIBE
>>>
>>>   Then a function type for a notification handler pointer:
>>>
>>>   + typedef void (*sane_option_change_callback)(SANE_Int option, void *value);
>>>
>>>   Having these minor API changes, it's become possible to make a call to
>>> sane_control_option() like the following:
>>>
>>>   sane_control_option(sane_handle, option_number, SANE_ACTION_SUBSCRIBE, my_handler, NULL);
>>>
>>>   And if the option option_number is marked as SANE_CAP_DYNAMIC in the
>>> option descriptor, the backend should setup the given notification
>>> handler and invoke it each time the option is updated.
>>>   For options not explicitly marked as dynamic it should return
>>> SANE_STATUS_UNSUPPORTED. So, no changes are required for the present
>>> backends.
>>>
>>>   How the backend could monitor the option changes? It's up to the
>>> backend. But with the present codebase/hardware polling would be used
>>> most of the time, I guess. That will be, however, a local-only polling
>>> over USB or SCISI interfaces, not a polling over the network as the
>>> backend code runs on the server connected to the scanner in the
>>> client-server scenario. Of course we also need to implement the proper
>>> RPC in order to support callbacks over the network, but that doesn't
>>> affect the backends and doesn't require more API changes.
>>>
>>>   As to a resident polling process inside the backend, we already have
>>> sanei_thread_*() functions for that.
>>>
>>
>>
>> --
>> "well, I stand up next to a mountain- and I chop it down with the edge of my hand"
> 
> 
>