use warnings;
use strict;
use Fcntl qw/:flock/;
use Data::Dumper;

sub write_log {
	my ($file, $obj) = @_;
	open my $fh, '>>', $file or die "open $file: $!";
	flock($fh, LOCK_EX) or die "flock $file: $!";
	print {$fh} Data::Dumper->new([$obj])->Useqq(1)->Dump
		or die "print $file: $!";
	close $fh or die "close $file: $!";
}

write_log("/tmp/log.txt", {hello=>"world"});