my $lock_path = $self->{lock_path};
croak 'already locked '.($lock_path // '(undef)') if $self->{lockfh};
return unless defined($lock_path);
- sysopen(my $lockfh, $lock_path, O_WRONLY|O_CREAT) or
+ sysopen(my $lockfh, $lock_path, O_RDWR|O_CREAT) or
croak "failed to open $lock_path: $!\n";
flock($lockfh, LOCK_EX) or croak "lock $lock_path failed: $!\n";
$self->{lockfh} = $lockfh;