Re: [RFC PATCH 2.6.17-mm1 4/3] ieee1394: convert ieee1394_transactions from semaphores to waitqueue

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

I wrote on 2006-06-24:
> +	return wait_event_interruptible(tlabel_wq,
> +					!hpsb_get_tlabel_atomic(packet));

Hmm. "Linux Device Drivers" says about wait_event_interruptible(wq, 
condition): ''Note that @condition may be evaluated an arbitrary number 
of times, so it should not have any side effects.''

Alas the hpsb_get_tlabel_atomic() _does_ have a side effect, but only 
when !hpsb_get_tlabel_atomic(packet) is true.

The current implementation of wait_event_interruptible() seems to 
evaluate @condition multiple times if it is false but only _once_ while 
it is true. May I rely on this fact or do I have to rewrite the 
condition to be completely free of side effects?

I don't believe there would be ever a sensible implementation of 
wait_event_interruptible() which would evaluate @condition again after 
it became true.

Thanks,
--
Stefan Richter
-=====-=-==- -==- ==--=
http://arcgraph.de/sr/
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