=head1 NAME

XSConfig - Fast XS drop-in replacement for Config.pm with perfect hashing.

=head1 VERSION

Version 6.27

=head1 SYNOPSIS

The Config.pm included by default with Perl is pure Perl.  Nearly all Perl apps
will load Config.pm.  For a number of reasons, of speed and memory space,
reimplement the P5P shipped Config.pm as an XS library, shareable between
processes as read-only memory, and with a hash that is better optimized than
Perl hashes, courtesy of gperf tool which generates collision-free perfect
hashes.

This module is a drop-in replacement for Config.pm. All code that does

    use Config;

will use the XS implementation after installing this module.  To revert to the
original pure perl Config.pm, go and delete the following 3 files that will be
next to each other in /site, Config.pm, Config_mini.pl, Config_xs_heavy.pl, and
the Config shared library in /auto, after deleting the /site files, the original
pure perl Config.pm in /lib will be loaded.

Since XS Config is a compiled C shared library, it can not be edited with a text
editor after it is built.  To change the values in the XS Config module,
edit the pure perl Config_heavy.pl file with a text editor and rebuild XS
Config.

IT IS HIGHLY RECOMMENDED THAT YOU HAVE GPERF TOOL INSTALLED AND RUNNABLE FROM
YOUR PATH BEFORE INSTALLING XS CONFIG.

=head1 BENCHMARKS

    perl -MXSLoader -MConfig -E"say $Config{ccflags}; sleep 1000"

    Memory Usage KB	Total	Image Committed	Image Private	Heap Private
    With PP Config	34,468	8,020		204		1120
    With XS Config	33,564	8,120		212		652

Using XSConfig 6.13, with a VC 2013 32 bit threaded perl, you save 468 KB of per
process memory, in exchange for 92 KB of shared between process, memory mapped
(Config.dll) memory. Even if you have just a single perl process ever running
on the machine at a time, you will still save 376 KB.

The total size of Config.dll in memory is 100 KB, with 8 KB of
unshareable memory, the rest is shared. The smallest (no XSUBs except boot)
Win32 XS DLL without taking special measures is 24 KB, with 8 KB of unshareable
memory. So around ~24 KB is the overhead of a Visual C 2013 DLL with all the
C compiler specific hidden static linked functions inside the DLL (these can
be removed, but it is "special measures" that aren't typical on Win32 Perls).

Onto performance, to slurp the entire tied %Config hash into a non-tied hash,
with XS Config is %36 faster than with PP Config. To read 1 key in the tied
%Config hash is 15% faster than with PP Config.

Raw data with XS Config

    C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
    $Config::VERSION.\"\n\";my %h; %h = %Config for 0..1000"
    6.13
    
    Version Number:   Windows NT 6.1 (Build 7601)
    Exit Time:        2:32 pm, Tuesday, February 2 2016
    Elapsed Time:     0:00:06.285
    Process Time:     0:00:06.271
    System Calls:     19974
    Context Switches: 4317
    Page Faults:      2334
    Bytes Read:       73084
    Bytes Written:    0
    Bytes Other:      8528
    
    C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
    $Config::VERSION.\"\n\";my $v; $v = $Config{'ccflags'} for 0..1000000;print
    $v"
    6.13
    -nologo -GF -W3 -O1 -MD -Zi -DNDEBUG -GL -DWIN32 -D_CONSOLE -DNO_STRICT -D_CRT_S
    ECURE_NO_DEPRECATE -D_CRT_NONSTDC_NO_DEPRECATE  -DPERL_TEXTMODE_SCRIPTS -DPERL_I
    MPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -DWIN32_NO_REGISTRY
    Version Number:   Windows NT 6.1 (Build 7601)
    Exit Time:        2:33 pm, Tuesday, February 2 2016
    Elapsed Time:     0:00:03.168
    Process Time:     0:00:03.151
    System Calls:     11223
    Context Switches: 2482
    Page Faults:      2070
    Bytes Read:       77180
    Bytes Written:    0
    Bytes Other:      7318

With PP Config

    
    C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
    $Config::VERSION.\"\n\";my %h; %h = %Config for 0..1000"
    5.023008
    
    Version Number:   Windows NT 6.1 (Build 7601)
    Exit Time:        2:34 pm, Tuesday, February 2 2016
    Elapsed Time:     0:00:09.907
    Process Time:     0:00:09.843
    System Calls:     39114
    Context Switches: 7145
    Page Faults:      3426
    Bytes Read:       118536
    Bytes Written:    0
    Bytes Other:      13446
    
    C:\sources>timeit -f t.dat perl -MXSLoader -MConfig -e"print
    $Config::VERSION.\"\n\";my $v; $v = $Config{'ccflags'} for 0..1000000;print
    $v"
    5.023008
    -nologo -GF -W3 -O1 -MD -Zi -DNDEBUG -GL -DWIN32 -D_CONSOLE -DNO_STRICT -D_CRT_S
    ECURE_NO_DEPRECATE -D_CRT_NONSTDC_NO_DEPRECATE  -DPERL_TEXTMODE_SCRIPTS -DPERL_I
    MPLICIT_CONTEXT -DPERL_IMPLICIT_SYS -DWIN32_NO_REGISTRY
    Version Number:   Windows NT 6.1 (Build 7601)
    Exit Time:        2:35 pm, Tuesday, February 2 2016
    Elapsed Time:     0:00:03.755
    Process Time:     0:00:03.744
    System Calls:     12721
    Context Switches: 3152
    Page Faults:      1392
    Bytes Read:       113612
    Bytes Written:    0
    Bytes Other:      6674

=head1 AUTHOR

Daniel Dragan C<< <BULKDD at cpan.org> >>
Reini Urban C<< <rurban at cpanel.net> >>

=head1 LICENSE AND COPYRIGHT

Copyright (C) 2015, Daniel Dragan
Copyright (C) 2015, cPanel Inc
 
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
