package Thread::Serialize;

$VERSION= '0.14';

# be as strict as possble
use strict;

# modules that we need
use load;
use Storable ();

# use ourselves to determine signature
our $iced;
if ( $Thread::Serialize::no_external_perl ) {
    $iced= unpack( 'l',Storable::freeze( [] ));
    $Thread::Serialize::no_external_perl= 'Signature obtained locally';
}

# use external perl to create signature
else {
    open( my $handle,
      qq($^X -MStorable -e "print unpack('l',Storable::freeze( [] ))" | )
    ) or die "Cannot determine Storable signature\n";
    $iced= readline $handle;
}

# satisfy -require-
1;

# The following subroutines are loaded on demand only

__END__

#-------------------------------------------------------------------------------
# freeze
#
# Freeze given parameters into a single scalar value
#
#  IN: 1..N parameters to freeze
# OUT: 1 frozen scalar

sub freeze {

    # something to be frozen
    if (@_) {

        # any of the parameters is special, so really freeze
        foreach (@_) {
            return Storable::freeze( \@_ ) if !defined() or ref() or m#\0#;
        }

        # just concatenate with null bytes (WAY faster)
        return join( "\0", @_ );
    }

    # no parameters, so just undef
    return;
} #freeze

#-------------------------------------------------------------------------------
#  IN: 1 frozen scalar to defrost
# OUT: 1..N thawed data structure

sub thaw {

    # nothing here or not interested
    return if !defined( $_[0] ) or !defined(wantarray);

    # return as list
    if (wantarray) {
        return ( unpack( 'l', $_[0] ) || 0 ) == $iced
          ? @{ Storable::thaw( $_[0] ) }
          : split "\0", $_[0];
    }

    # scalar, really frozen, return first value
    elsif ( ( unpack( 'l',$_[0] ) || 0 ) == $iced ) {
        return Storable::thaw( $_[0] )->[0];
    }

    # return first part of scalar
    return $_[0] =~ m#^([^\0]*)# ? $1 : $_[0];
} #thaw

#-------------------------------------------------------------------------------
#
# Standard Perl Features
#
#-------------------------------------------------------------------------------

sub import {
    shift;

    # determine namespace and subs
    my $namespace= caller().'::';
    @_= qw( freeze thaw ) if !@_;

    # do our exports
    no strict 'refs';
    *{$namespace.$_}= \&$_ foreach @_;

    return;
} #import

#-------------------------------------------------------------------------------

__END__

=head1 NAME

Thread::Serialize - serialize data-structures between threads

=head1 SYNOPSIS

  use Thread::Serialize;    # export freeze() and thaw()

  use Thread::Serialize (); # must call fully qualified subs

  my $frozen = freeze( any data structure );
  any data structure = thaw( $frozen );

=head1 VERSION

This documentation describes version 0.14.

=head1 DESCRIPTION

                  *** A note of CAUTION ***

 This module only functions on threaded perl or an unthreaded perl
 with the "forks" module installed.

 Please also note that this documentation describes the "maint" version
 of this code.  This version is essentially frozen.  Please use a 5.14
 or higher version of perl for the "blead" version of this code.

                  *************************

The Thread::Serialize module is a library for centralizing the routines
used to serialize data-structures between threads.  Because of this central
location, other modules such as L<Thread::Conveyor>, L<Thread::Pool> or
L<Thread::Tie> can benefit from the same optimilizations that may take
place here in the future.

=head1 SUBROUTINES

There are only two subroutines.

=head2 freeze

 my $frozen = freeze( $scalar );

 my $frozen = freeze( @array );

The "freeze" subroutine takes all the parameters passed to it, freezes them
and returns a frozen representation of what was given.  The parameters can
be scalar values or references to arrays or hashes.  Use the L<thaw>
subroutine to obtain the original data-structure back.

=head2 thaw

 my $scalar = thaw( $frozen );

 my @array = thaw( $frozen );

The "thaw" subroutine returns the data-structure that was frozen with a call
to L<freeze>.  If called in a scalar context, only the first element of the
data-structure that was passed, will be returned.  Otherwise the entire
data-structure will be returned.

It is up to the developer to make sure that single argument calls to L<freeze>
are always matched by scalar context calls to L<thaw>.

=head1 REQUIRED MODULES

 load (0.10)
 Storable (any)

=head1 OPTIMIZATIONS

To reduce memory and CPU usage, this module uses L<load>.  This causes
subroutines only to be compiled in a thread when they are actually needed at
the expense of more CPU when they need to be compiled.  Simple benchmarks
however revealed that the overhead of the compiling single routines is not
much more (and sometimes a lot less) than the overhead of cloning a Perl
interpreter with a lot of subroutines pre-loaded.

To reduce the number of modules and subroutines loaded, an external Perl
interpreter is started to determine the Storable signature at compile time.
In some situations this may cause a problem: please set the
C<$Thread::Serialize::no_external_perl> variable to a true value at compile
time B<before> loading Thread::Serialize if this causes a problem.

 BEGIN { $Thread::Serialize::no_external_perl= 1 }
 use Thread::Serialize;

=head1 KNOWN ISSUES

=head2 Embedded Perls

Philip Monsen reported that in the case of an embedded Perl interpreter (e.g.
in a C program), the use of an external executor to determine the Storable
signature, causes problems.  This has been fixed by introducing the global
variable C<$Thread::Serialize::no_external_perl> (see L<OPTIMIZATIONS>).

=head1 AUTHOR

Elizabeth Mattijsen, <liz@dijkmat.nl>.

Please report bugs to <perlbugs@dijkmat.nl>.

=head1 COPYRIGHT

Copyright (c) 2002, 2003, 2004, 2010, 2012 Elizabeth Mattijsen <liz@dijkmat.nl>.
All rights reserved.  This program is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.

=head1 SEE ALSO

L<load>, L<Thread::Conveyor>, L<Thread::Pool>, L<Thread::Tie>.

=cut