We should keep this on the list since other people besides me can
answer this question, perhaps quicker too, and it might be of general
interest.
On Jul 6, 2006, at 1:55 PM, pix wrote:
> hey hans,
>
> i was wondering if you have experienced this behaviour where, on
> linux,
> the hid the hid object hangs if the device disappears (even only
> briefly) while hid has it open?
>
> i thought it might have just been the problem that the device was
> getting a new device file name when it returned, but i have now done
> some udev trickery to make sure the steim junxion box we are using
> always gets the same event number, and the problem still persists.
>
> once the device disappears hid no longer responds to close or open
> messages.
>
> it would be cool if there was a work around because we occasionally
> have
> problems with the junxion box we are using 'winking out' for just long
> enough for linux to kill off the device.
Hmm, I haven't seen that, but its not surprising that it would hang.
Basically, the object is reading that file handle every 5 ms, or
whatever you set the poll time to. So if sometime reads from a non-
existant filehandle that's open, then it'll hang, no matter how you
are doing it.
I have used the junxionbox some and I haven't seen that problem. I
think the best way to solve that problem would be to figure out
what's causing the junxionbox to wink out. Its in beta test so I
think they would be interested to hear about that problem. I was
just at STEIM for three weeks working with Rene and Taku, who are
working on the junxionbox. Taku performs with his junxion-related
devices, so he's dealt with a lot of these issues.
I can't think of anything offhand as an easy workaround. You might
be able to test the filehandle before reading from it, but I am
worried about the overhead that might introduce. A key part of hid
is making it as low latency as possible, and not to take a ton of
CPU. Such a check might be pretty minimal but running it 200 times a
second adds up. Can any of the big time Linux heads think of a way
to deal with this?
.hc
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