Re: An Inline question, and a user's experience: Fwd: Using Inline::CPP and Math::Primes::FastSieve

The use vs. require issue is a little harder when I have chains of
modules, or things get loaded my Moose/Mouse roles via 'with' since
they load at runtime.  In my immediate use, looking for
Math::Prime::FastSieve is all inside a Role, so there's no real way I
can change how it is loaded.  Even if I write:

  use Math::Prime::FastSieve;
  # .... use MPFS

in my role, I get the warning.  No direct eval or require on my part.


The chain of modules example, with MyPack.pm:

  package MyPack;
  use strict;
  use warnings;
  use Math::Prime::FastSieve;
  # ...
  1;

Everything is good.  No warnings.  But along comes someone who wants
to use Mypack and creates his MyScript:

  #!/usr/bin/env perl
  no strict;
  no warnings;
  require MyPack;
  # ...

Oops, they get the warning.  Similarly if they use an eval with use or
require, and 'no warnings' doesn't work for suppression.

As you wrote, putting 'Inline->init()' after the inclusion of M::P::FS
solves the issue in both cases.  I can do this successfully:

if (eval {require Math::Prime::FastSieve; Inline->init(); 1;}) {
   # We have MPFS, do fast stuff.
} else {
   ...
}

The goal would be to have Inline handle it, or the module using Inline
(e.g. Math::Prime::FastSieve) do it.  But for now this works.

Dana


On Sat, May 19, 2012 at 12:52 PM, Sisyphus <[email protected]> wrote:
>
> ----- Original Message ----- From: "David Oswald"
>
>> I get the Inline M51 warning (DATA section not used) if anyone does a
>> require on my module. I realize this is a harmless warning, but I
>> really don't want it happening to my module when I don't even use
>> Inline. So for now I've disabled use of MPFS to avoid it.
>>
>> <snip>------------------------------------------------
>>
>> That message is coming from Inline, but I can't figure out how one
>> might squelch it.  Are there any suggestions that might help here?
>
>
> Found the time to have a further look tonight.
>
> It all happens in this section of Inline.pm:
>
> ######################################################
> #==============================================================================
> # Process delayed objects that don't have source code yet.
> #==============================================================================
> # This code is an ugly hack because of the fact that you can't use an
> # INIT block at "run-time proper". So we kill the warning for 5.6+ users
> # and tell them to use a Inline->init() call if they run into problems.
> (rare)
> my $lexwarn = ($] >= 5.006) ? 'no warnings;' : '';
>
> eval <<END;
> $lexwarn
> \$INIT = \$INIT; # Needed by Sarathy's patch.
> sub INIT {
>   \$INIT++;
>   &init;
> }
> END
>
> sub init {
>   local ($/, $") = ("\n", ' '); local ($\, $,);
>
>   while (my $o = shift(@DATA_OBJS)) {
> $o->read_DATA;
> $o->glue;
>   }
> }
>
> sub END {
>   warn M51_unused_DATA() if @DATA_OBJS;
>   print_version() if $version_requested && not $version_printed;
> }
>
> #######################################################
>
> If @DATA_OBJS doesn't get emptied out then you get the M51 warning.
>
> If you "require" Math::Prime::FastSieve, sub INIT does not get called
> (because INIT blocks can only be executed *before* runtime), therefore sub
> init doesn't get called, therefore @DATA_OBJS doesn't get emptied, therefore
> you get the M51 warning.
>
> One solution is to take the advice offered in the comments in the above code
> and have FastSieve.pm do:
>
> Inline->init();
>
> (immediately prior to the closing '1;' seems to suffice).
>
> I'm a bit nervous about messing too much with this code - I don't know what
> "Sarathy's patch" is, or why it needs the line of code that is claimed to be
> necessary. I've no idea why it does '\$INIT++;' (or even why $INIT has to
> exist) and I don't really know much about how that code fits in to the
> general scheme.
>
> It's clear that $lexwarn can now be removed and replaced by an unconditional
> 'no warnings;' at the begining of the eval() ... and I'll do that.
>
> For the moment, I think I'll just document the 'Inline->init()' solution,
> and leave it at that.
>
> Eventually I'd like to think that I'll get around to poking and prodding a
> bit, and try to come up with a better way of silencing the M51 warning when
> an Inline module is "required". (If someone else gets to it before I do,
> then that's all the better :-)
>
> Cheers,
> Rob
>
> PS If it's not obvious, the reason that 'use Math::Prime::FastSieve;' does
> *not* produce the same
> warning is that loading with "use" enables the INIT sub to get run (straight
> after compile-time,
> and before runtime). Therefore, @DATA_OBJS gets emptied out, and the M51
> warning is avoided.