Bug#484021: perl: evaluation of errno ($!) violates priniciple of DWIM

[Dominic Hargreaves]

On Mon, Jun 02, 2008 at 01:29:15AM +0100, Stephen Gran wrote:
> This one time, at band camp, Brendan O'Dea said:
> > On Mon, Jun 2, 2008 at 8:20 AM, Stephen Gran <sgran at debian.org> wrote:
> > > perl should clear errno before going into a function where the API
> > > depends on checking it afterwards.  Yes, I am aware there are other ways
> > > to determine that the setegid call failed.  The problem is that the
> > > documentation tells me that the correct way to evaluate failure is to
> > > check errno after calls, and the call fails to initialize errno
> > > correctly.  Either the docs or the function are wrong.
> > 
> > Normal POSIX behaviour is for errno only to be set on error, never
> > cleared.  See errno(3): "[...] errno is never set to zero by any
> > library function."  I would be surprised if Perl changed this
> > behaviour.
> 
> Yes, of course.  The bug isn't only about perl not resetting errno, it's
> that either the docs or the function are wrong.  Since the docs tells me
> that the way to tell if the call failed is to evaluate errno, then the
> doc is wrong (as it is now).  I would additionally expect the perl DWIM
> thing to mean that $! is only ever set if the last call failed, but doing
> that would just be a bonus - that's not the main point of this report.
> Even a pointer somewhere that perl will not clear errno, and that every
> time you call a function that relies on passing back information in $!,
> you must explicitly clear it afterwards would be an improvement.
> 
> > Suggest that you explicitly initialise $! to 0.
> 
> Yes, I had already discovered that undef $! works just fine to work
> around this behavior, but it is surprising behavior, given the lengths
> perl goes to in other places, and given the documentation.

Does the change in 
<http://perl5.git.perl.org/perl.git/commitdiff/a73bef7?hp=7f8d58fb0a9806bbceb2f22543b4599f3d791699>

address your concerns?

Thanks,
Dominic.

-- 
Dominic Hargreaves | http://www.larted.org.uk/~dom/
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