$VAR1 = bless({'options' => 
        {'filehandle' => 
         bless( \*Symbol::GEN2, 'FileHandle' ),
        'filename' => 'a.log'},}, 'Log' );

##</code><code>##

$self->do_task()

##</code><code>##

Process::spawn(\&do_task, $self);

##</code><code>##

$new_log = new Log(filename => 'new.log');
$cur_log = $self->{log};
$self->{log} = $new_log;
Process::spawn(\&do_task, $self); # This runs in background.
$self->{log} = $cur_log; # Restore.

##</code><code>##

$self->{system}->{log},
$self->{filecache}->{system}->{log}

##</code><code>##

@ref = Devel::ObjSearch($self, 
sub { return UNIVERSAL::isa($_[0], 'Log'); });
foreach (@ref) { $_->filename('new.log'); $_->filehandle($new_log); }
.. spawn() ..