Re: lib/poll.c bug?

[Eric Blake]

On 06/29/2011 11:31 AM, Erik Faye-Lund wrote:
> POSIX says the following about poll "A value of 0 indicates that the
> call timed out and no file descriptors have been selected.". My
> interpretation is that a return value of 0 would be illegal when
> timeout = -1.
> 
> But when I call poll(..., -1), it seems 0 is returned under some
> conditions. Looking through the code, it seems that there isn't any
> efforts to enforce this paragraph; perhaps the included patch is
> appropriate?
> 
> This problem currently affects a feature-branch I have against Git for
> Windows, where this cause a program not to consume input because it
> assumes that poll(..., -1) cannot return 0. The patch fixes it for me.

I think there's a bigger problem here, which is that there is no way to
poll on pipes without busy-waiting, at least not with our current poll
replacement code.  Your patch would turn poll into a 100% cpu hog in the
cases where it is now returning 0.

See this previous discussion:
http://lists.gnu.org/archive/html/bug-gnulib/2011-06/msg00010.html

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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