#! perl -slw
use Time::HiRes qw[ time ];
use threads qw[ stack_size 4096 ];

my $file = 'theFile';

async{ 1 until -e $file; }->detach for 1 .. 300;

sleep 3;

my @times = time;
unless( -e $file ) {
    push @times, time;
    open FILE, '>', $file or die "$file : $!";
    push @times, time;
    close FILE;
}
push @times, time;

print for @times;

unlink $file;

__END__
[20:51:05.40] C:\test>junk49
1285789900.703
1285789900.87509
1285789901.02394
1285789901.324