There's really nothing to explain. It does exactly what you asked for by calling select RBITS,WBITS,EBITS,TIMEOUT.

Note that IO::Select is easier to use than select.

use IO::Select ();

my $sel = IO::Select->new($MySocket);
my @read = $sel->can_read(3)
   or die("Time out!\n");

$MySocket->recv($text);
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