Re: [uml-devel] Occasional hang starting up.

[Blaisorblade <blaisorblade@yahoo.it>]

On Friday 17 March 2006 22:27, Werner Almesberger wrote:
> Blaisorblade wrote:
> > 1) I'll try to fix poll(2) to return -EINVAL. Dunno whether anyone will
> > say "no, the app is stupid, it deserves no error", but hope not (with
> > "try" I refer to this). Attached patch should do this.
>
> I think the behaviour of "poll" with nfds = 0 is correct as it is.
> At least POSIX doesn't say anything to the extent that "nfds"
> couldn't be zero:

> http://www.opengroup.org/onlinepubs/009695399/functions/poll.html

I don't think that "hanging" is a correct behaviour anyway... unless the 
application *wanted* to wait for a signal, but this is a clumsy way to do 
this (I don't think there's any difference from pause()).

> Furthermore, this is one of several ways to implement a "sleep"
> function with sub-second granularity

> , so existing applications 
> may already depend on "poll" accepting nfds = 0. (Of course,
> they would probably be better off using "nanosleep".)

This is a very smart note, however usleep(3) exists since 4.3 BSD so this is a 
bit unlikely; however you're surely right on this.

> > 2) write_sigio_thread should do a "down" on a semaphore/mutex and the
> > first update_thread should "up" it.
>
> Yup :-)
>
> Thanks,
> - Werner

-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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