[sane-devel] sane_cancel and sane_read

[Henning Meier-Geinitz]

Hi,

On 2006-04-25 15:07, Wittawat Yamwong wrote:
> Should/must/may a frontend call sane_read after sane_cancel?

I think it may but it doesn't need to.
I can't find an explicit statement in the standard that it's forbidden
to do so. In fact, there is even a status code for sane_read for this
case. 

But it's also not necessary (and not really logical) to call sane_read
after sane_cancel(). 

> Case II: The frontend has read a block of image data from a backend and it is 
> writing the data to a file but a IO error occurs.
> The frontend probably calls 
> sane_cancel. What will/must the frontend do next? Will it call sane_read 
> until an error or EOF occurs?

It should do nothing (or call sane_close, sane_exit).

> This is important to my backend (pixma). It would be much more complex if 
> frontends are not required to call sane_read after sane_cancel because I have 
> to check whether sane_cancel was called synchronously or asynchronously. If 
> it's called synchronously (case II), an outstanding scan operation must be 
> completely canceled before sane_cancel returns. If it's call asynchronously 
> (case I), the request must be postponed by setting a flag for example. The 
> request will be carried out when we return to the reader thread.

Why not just kill the reader process in sane_cancel? Do you think the
way this is done in the existing backends (e.g. mustek) is wrong?

Bye,
  Henning