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#-*- perl -*-
#
# Copyright (C) 2001 Ken'ichi Fukamachi
# All rights reserved. This program is free software; you can
# redistribute it and/or modify it under the same terms as Perl itself.
#
# $Id$
# $FML$
#
package IO::File::Atomic;
use strict;
use vars qw(@ISA @EXPORT @EXPORT_OK);
use Carp;
use IO::File;
require Exporter;
@ISA = qw(IO::File);
BEGIN {}
END {}
=head1 NAME
IO::Atomic - atomic operation
=head1 SYNOPSIS
use IO::Atomic;
my $wh = IO::Atomic->open($file);
print $wh "new/updated things ...";
$wh->close;
So, in usual cases, you use in this way.
use FileHandle;
use IO::Atomic;
# get read handle for $file
my $rh = new FileHandle $file;
# get handle to update $file
my $wh = IO::Atomic->open($file);
while (<$rh>) {
print $wh "new/updated things ...";
}
$wh->close;
$rh->close;
You can use this method to open $file for both read and write.
use IO::Atomic;
my ($rh, $wh) = IO::Atomic->rw_open($file);
while (<$rh>) {
print $wh "new/updated things ...";
}
$wh->close;
$rh->close;
To copy from $src to $dst,
IO::File::Atomic->copy($src, $dst) || croak("fail to copy");
=head1 DESCRIPTION
=cut
# Descriptions: constructor
# forward new() request to superclass (IO::File)
# Arguments: $class_name
# Side Effects: none
# Return Value: class object
# XXX $self is blessed file handle.
sub new
{
my ($self) = shift;
my $me = $self->SUPER::new();
$me->open(@_) if @_;
$me;
}
# Descriptions: open( $file [, $mode] )
# open not $file but file.new.$$
# forward open() request to IO::File class
# Arguments: $self $file [$mode]
# XXX $self is blessed file handle.
# Side Effects: create ${ *$self } hash to save status information
# Return Value: write file handle (for $file.new.$$)
sub open
{
my ($self, $file, $mode) = @_;
# get an instance
ref($self) or $self = $self->new;
# default mode is "w"
$mode ||= "w";
# temporary file
my $temp = $file.".new.".$$;
${*$self}{ _orig_file } = $file;
${*$self}{ _temp_file } = $temp;
# real open with $mode
$self->autoflush;
$self->SUPER::open($temp, "w") ? $self : undef;
}
# Descriptions: open $file with the mode $mode for both
# reading and writing.
# Arguments: $class_name $file [$mode]
# Side Effects: none
# Return Value: LIST of file handle (read, write)
sub rw_open
{
my ($self, $file, $mode) = @_;
use FileHandle;
my $rh = new FileHandle $file;
my $wh = $self->open($file, $mode);
return ($rh, $wh);
}
# Descriptions: close "write" file handle
# XXX "read" file handle is closed by SUPERCLASS.
# Arguments: $self
# XXX $self is blessed file handle.
# Side Effects: rename the temporary file to the original file
# save the error message in ${ *$fh }
# Return Value: 1 if succeeded, 0 if failed
sub close
{
my ($self) = @_;
my $fh = $self;
my $orig = ${ *$fh }{ _orig_file };
my $temp = ${ *$fh }{ _temp_file };
# XXX close the "write" file handle (write .. to $temp file)
close($fh);
if (rename($temp, $orig)) {
return 1;
}
else {
${ *$fh }{ _error } = "fail to rename($temp, $orig)";
return 0;
}
}
# Descriptions: copy file, which ensures atomic operation
# Arguments: $self source_file destination_file
# Side Effects: $dst's file mode becomes the same as $src
# Return Value: 1 if succeeded, undef if not
sub copy
{
my ($self, $src, $dst) = @_;
my ($mode) = (stat($src))[2];
my $rh = new FileHandle $src;
my $wh = $self->open($dst);
if (defined($rh) && defined($wh)) {
while (sysread($rh, $_, 4096)) { print $wh $_;}
$wh->close;
$rh->close;
chmod $mode, $dst;
}
else {
return undef;
}
}
# Descriptions: return error message
# Arguments: $self
# XXX $self is blessed file handle.
# Side Effects: none
# Return Value: error message string
sub error
{
my ($self) = @_;
my $fh = $self;
${ *$fh }{ _error };
}
# Descriptions: reset the previous work
# Arguments: $self
# XXX $self is blessed file handle.
# Side Effects: clean up the previous work ;-)
# remove temporary files we created
# Return Value: none
sub rollback
{
my ($self) = @_;
my $fh = $self;
my $temp = ${ *$fh }{ _temp_file };
if (-f $temp) { unlink $temp;}
}
# Descriptions: destructor
# forward the request to rollback() in this class
# Arguments: $self
# XXX $self is blessed file handle.
# Side Effects: none
# Return Value: the same as rollback()
sub DESTROY
{
my ($self) = @_;
$self->rollback;
}
=head1 AUTHOR
Ken'ichi Fukamachi
=head1 COPYRIGHT
Copyright (C) 2001 Ken'ichi Fukamachi
All rights reserved. This program is free software; you can
redistribute it and/or modify it under the same terms as Perl itself.
=head1 HISTORY
IO::File::Atomic.pm appeared in fml5.
=cut
1;
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