Re: [PATCH 3/4] maint: pick XSI funcs at runtime, not configure time.

[Gary V. Vaughan]

Hi Peter,

On 28 Nov 2011, at 18:05, Peter Rosin wrote:
> Gary V. Vaughan skrev 2011-11-28 10:20:
>> On 28 Nov 2011, at 15:48, Peter Rosin wrote:
>>> Gary V. Vaughan skrev 2011-11-25 09:57:
>>>> Determine, on a function by function basis, what XSI features
>>>> are available in the shell that is actually running the script,
>>>> rather than the one that was picked at configure time by the
>>>> re-execution engine.
>>> 
>>> Doesn't this mean that the libtool script will do a number of
>>> extra forks each time it is run?
>> 
>> Well, yes and no.  There will be an extra 4 or 8 evals (depending
>> on whether the XSI function is chosen) as libtool starts up when
> 
> That's the evals in sub-shells, right? Those with this pattern:
> 
>       if $_use_fast_funcs && (eval ...) 2>/dev/null
>       then
>         eval '...
> 
> or this:
> 
>       if (eval ...) 2>/dev/null
>       then
>         eval '...

Yes, that's them.

>> [[snip]]
>>> If that's the case, I would like
>>> to know how that impacts the execution time on Cygwin/MinGW...
>> 
>> I don't have access to Windows so I can't actually measure it, but
>> I doubt that the difference will be noticeable for even a large
>> project, and quite possibly a small project like libltdl that only
>> runs libtool a hand full of times will actually be (imperceptibly)
>> faster.
> 
> I think you are underestimating the Cygwin fork pain.
> 
> BTW, libltdl runs libtool more like 20 times, but I agree it's very
> small and the number of forks will not matter much.
> 
> My typical use case is "mid-sized" at a magnitude or so larger, and
> even there with a fork rate of approx 10-15 Hz as I'm seeing, it wouldn't
> be too harsh with a couple of extra forks - a minutes or so on the
> wall clock time. But it would really add to the pain on some
> (hypothetical?) large project with thousands of libtool invocations.
> That's all I'm saying, but *I* am not building any of those...

Maybe I should switch the sense of the _use_fast_funcs, so that the
pattern becomes:

  if $libtool_force_fast_funcs || (eval ...) 2>/dev/null
  then
     eval '...

And then recommend that cygwin users always use an XSI and += capable
shell, with libtool_force_fast_funcs=: in the environment to cut out the
forks?

> Hmm, looking closer, shouldn't _use_fast_funcs have some kind of lt
> prefix?

Good point.  I'll add a prefix before pushing.  Thanks.

Cheers,
-- 
Gary V. Vaughan (gary AT gnu DOT org)