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use strict;
use warnings;
...
} else {
    print("Error ", 0+$!, ": $!\n");
}

Win>perl a.pl
Error 0:

linux$ perl a.pl
Error 29: Illegal seek

use strict;
use warnings;
...
} else {
    print("Timeout\n");
}

Win>perl a.pl 0
Timeout
...

linux$ perl a.pl 1
select: (9) Bad file descriptor

- if(select($rb,$wb,$eb,$t) > 0)
+ if(select($rb,$wb,$eb,$t) >= 0)

use strict;
use warnings;
...
    print("Num writers ready: ", 0+@$w_ready, "\n");
    print("Num errors  ready: ", 0+@$e_ready, "\n");
}