package JSONFile;

use strict;
use warnings;
use JSON;
use IO::File;
use Fcntl qw(:flock);
use Carp;

sub new{
    my $class = shift;
    my %cfg = (
        lock => 0,
        file => '',
        mode => O_RDONLY,
    @_);
    eval{
        my $fh = IO::File->new;
        $fh->open($cfg{file}, $cfg{mode}) or croak "Error open file '$cfg{file}', $!";
        if($cfg{lock}){ flock($fh, LOCK_EX)|| carp "Problem mit LOCK_EX, $!" }
        bless{
            FH  => $fh,
            CFG => \%cfg,
            JSN => JSON->new
        }, $class;
    }
}

sub freeze{
    my $self = shift;
    my $ref  = shift;
    $self->{FH}->truncate(0);
    $self->{FH}->seek(0,0);
    $self->{FH}->print( $self->{JSN}->encode($ref) );
}

sub thaw{
    my $self = shift;
    $self->{FH}->seek(0,0);
    read($self->{FH}, my $raw, -s $self->{FH});
    $self->{JSN}->decode($raw);
}
1;#########################################################################
__END__
use Data::Dumper;

my $f = JSONFile->new(
    file => "d:/tmp/xdata.jn", 
    mode => O_CREAT|O_RDWR, 
    lock => 1
) or die $@;

$f->freeze(['ä']);
my $r = $f->thaw;
print "@$r";