I do not "use threads" in my code. Whether it makes sense or not (it certainly doesn't to me), the fact is that this works:

system("xspec - ${tmp}.xcm");

open(DAT, "${tmp}xsfit.dat") || die ("Could not open file!");

whereas this does not:

bjmsys("xspec - ${tmp}.xcm", $v);

open(DAT, "${tmp}xsfit.dat") || die ("Could not open file!");

where------------

sub bjmsys {

my $arg=shift;

my $v=shift;

$v=0 unless defined $v;

my $status;

print "$arg\n" if $v>1||$v<0;

$status=system("$arg");

print "return status = $status\n" if $v>1;

return $status;

}