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Text File | 1999-12-28 | 9.4 KB | 288 lines

;# $Id: Storable.pm,v 0.5 1997/06/10 16:38:37 ram Exp $
;#
;#  Copyright (c) 1995-1997, Raphael Manfredi
;#
;#  You may redistribute only under the terms of the Artistic License,
;#  as specified in the README file that comes with the distribution.
;#
;# $Log: Storable.pm,v $
;# Revision 0.5  1997/06/10  16:38:37  ram
;# Baseline for fifth alpha release.
;#

require DynaLoader;
require Exporter;
package Storable; @ISA = qw(Exporter DynaLoader);

@EXPORT = qw(store retrieve);
@EXPORT_OK = qw(
    nstore store_fd nstore_fd retrieve_fd
    freeze nfreeze thaw
    dclone
);

use AutoLoader;
use Carp;
use vars qw($forgive_me $VERSION);

$VERSION = '0.5';
*AUTOLOAD = \&AutoLoader::AUTOLOAD;        # Grrr...

bootstrap Storable;
1;
__END__

sub store {
    return _store(0, @_);
}

sub nstore {
    return _store(1, @_);
}

sub _store {
    my $netorder = shift;
    my $self = shift;
    my ($file) = @_;
    croak "Not a reference" unless ref($self);
    croak "Too many arguments" unless @_ == 1;    # Watch out for @foo in arglist
    local *FILE;
    open(FILE, ">$file") || croak "Can't create $file: $!";
    binmode FILE;
    my $ret;
    eval { $ret = $netorder ? net_pstore(FILE, $self) : pstore(FILE, $self) };
    close(FILE) or $ret = undef;
    unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
    croak $@ if $@ =~ s/\.?\n$/,/;
    return $ret ? $ret : undef;
}

sub store_fd {
    return _store_fd(0, @_);
}

sub nstore_fd {
    my ($self, $file) = @_;
    return _store_fd(1, @_);
}

sub _store_fd {
    my $netorder = shift;
    my $self = shift;
    my ($file) = @_;
    croak "Not a reference" unless ref($self);
    croak "Too many arguments" unless @_ == 1;    # Watch out for @foo in arglist
    my $fd = fileno($file);
    croak "Not a valid file descriptor" unless defined $fd;
    my $ret;
    eval { $ret = $netorder ? net_pstore($file, $self) : pstore($file, $self) };
    croak $@ if $@ =~ s/\.?\n$/,/;
    return $ret ? $ret : undef;
}

sub freeze {
    _freeze(0, @_);
}

sub nfreeze {
    _freeze(1, @_);
}

sub _freeze {
    my $netorder = shift;
    my $self = shift;
    croak "Not a reference" unless ref($self);
    croak "Too many arguments" unless @_ == 0;    # Watch out for @foo in arglist
    my $ret;
    eval { $ret = $netorder ? net_mstore($self) : mstore($self) };
    croak $@ if $@ =~ s/\.?\n$/,/;
    return $ret ? $ret : undef;
}
sub retrieve {
    my ($file) = @_;
    local *FILE;
    open(FILE, "$file") || croak "Can't open $file: $!";
    binmode FILE;
    my $self;
    eval { $self = pretrieve(FILE) };        # Call C routine
    close(FILE);
    croak $@ if $@ =~ s/\.?\n$/,/;
    return $self;
}

sub retrieve_fd {
    my ($file) = @_;
    my $fd = fileno($file);
    croak "Not a valid file descriptor" unless defined $fd;
    my $self;
    eval { $self = pretrieve($file) };        # Call C routine
    croak $@ if $@ =~ s/\.?\n$/,/;
    return $self;
}

sub thaw {
    my ($frozen) = @_;
    my $self;
    eval { $self = mretrieve($frozen) };    # Call C routine
    croak $@ if $@ =~ s/\.?\n$/,/;
    return $self;
}

=head1 NAME

Storable - persistency for perl data structures

=head1 SYNOPSIS

    use Storable;
    store \%table, 'file';
    $hashref = retrieve('file');

=head1 DESCRIPTION

The Storable package brings you persistency for your perl data structures
containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
convenientely stored to disk and retrieved at a later time.

It can be used in the regular procedural way by calling C<store> with
a reference to the object to store, and providing a file name. The routine
returns C<undef> for I/O problems or other internal error, a true value
otherwise. Serious errors are propagated as a C<die> exception.

To retrieve data stored to disk, you use C<retrieve> with a file name,
and the objects stored into that file are recreated into memory for you,
and a I<reference> to the root object is returned. In case an I/O error
occurred while reading, C<undef> is returned instead. Other serious
errors are propagated via C<die>.

Since storage is performed recursively, you might want to stuff references
to objects that share a lot of common data into a single array or hash
table, and then store that object. That way, when you retrieve back the
whole thing, the objects will continue to share what they originally shared.

At the cost of a slight header overhead, you may store to an already
opened file descriptor using the C<store_fd> routine, and retrieve
from a file via C<retrieve_fd>. Those names aren't imported by default,
so you will have to do that explicitely if you need those routines.
The file descriptor name you supply must be fully qualified.

You can also store data in network order to allow easy sharing across
multiple platforms, or when storing on a socket known to be remotely
connected. The routines to call have an initial C<n> prefix for I<network>,
as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
correctly restored so you don't have to know whether you're restoring
from native or network ordered data.

When using C<retrieve_fd>, objects are retrieved in sequence, one
object (i.e. one recursive tree) per associated C<store_fd>.

If you're more from the object-oriented camp, you can inherit from
Storable and directly store your objects by invoking C<store> as
a method. The fact that the root of the to-be-stored tree is a
blessed reference (i.e. an object) is special-cased so that the
retrieve does not provide a reference to that object but rather the
blessed object reference itself. (Otherwise, you'd get a reference
to that blessed object).

=head1 MEMORY STORE

The Storable engine can also store data into a Perl scalar instead, to
later retrieve them. This is mainly used to freeze a complex structure in
some safe compact memory place (where it can possibly be sent to another
process via some IPC, since freezing the structure also serializes it in
effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
out and recreate the original complex structure in memory.

Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
If you wish to send out the frozen scalar to another machine, use
C<nfreeze> instead to get a portable image.

Note that freezing an object structure and immediately thawing it
actually achieves a deep cloning of that structure. Storable provides
you with a C<dclone> interface which does not create that intermediary
scalar but instead freezes the structure in some internal memory space
and then immediatly thaws it out.

=head1 SPEED

The heart of Storable is written in C for decent speed. Extra low-level
optimization have been made when manipulating perl internals, to
sacrifice encapsulation for the benefit of a greater speed.

Storage is usually faster than retrieval since the latter has to
allocate the objects from memory and perform the relevant I/Os, whilst
the former mainly performs I/Os.

On my HP 9000/712 machine running HPUX 9.03 and with perl 5.004, I can
store 0.8 Mbyte/s and I can retrieve at 0.72 Mbytes/s, approximatively
(CPU + system time).
This was measured with Benchmark and the I<Magic: The Gathering>
database from Tom Christiansen (1.9 Mbytes).

=head1 EXAMPLES

Here are some code samples showing a possible usage of Storable:

    use Storable qw(store retrieve freeze thaw dclone);

    %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);

    store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";

    $colref = retrieve('/tmp/colors');
    die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
    printf "Blue is still %lf\n", $colref->{'Blue'};

    $colref2 = dclone(\%color);

    $str = freeze(\%color);
    printf "Serialization of %%color is %d bytes long.\n", length($str);
    $colref3 = thaw($str);

which prints (on my machine):

    Blue is still 0.100000
    Serialization of %color is 102 bytes long.

=head1 WARNING

If you're using references as keys within your hash tables, you're bound
to disapointment when retrieving your data. Indeed, Perl stringifies
references used as hash table keys. If you later wish to access the
items via another reference stringification (i.e. using the same
reference that was used for the key originally to record the value into
the hash table), it will work because both references stringify to the
same string.

It won't work across a C<store> and C<retrieve> operations however, because
the addresses in the retrieved objects, which are part of the stringified
references, will probably differ from the original addresses. The
topology of your structure is preserved, but not hidden semantics
like those.

On platforms where it matters, be sure to call C<binmode()> on the
descriptors that you pass to Storable functions.

=head1 BUGS

You can't store GLOB, CODE, FORMLINE, etc... If you can define
semantics for those operations, feel free to enhance Storable so that
it can deal with those.

The store functions will C<croak> if they run into such references
unless you set C<$Storable::forgive_me> to some C<TRUE> value. In this
case, the fatal message is turned in a warning and some
meaningless string is stored instead.

Due to the aforementionned optimizations, Storable is at the mercy
of perl's internal redesign or structure changes. If that bothers
you, you can try convincing Larry that what is used in Storable
should be documented and consistently kept in future revisions.
As I said, you may try.

=head1 AUTHOR

Raphael Manfredi F<E<lt>[e-mail]<gt>>

=cut