$rv = $io->block(); ## Find out the current setting
if( !$rv ) {
   ## Is non-blocking enabled or did the call fail?
}

$rv = $io->blocking( 1 ); ## Turn on blocking (turn off non-blocking)
if( !$rv ) { 
    ## Was non-blocking previously enabled or did the call fail?
}

$rv = $io->blocking( 0 ); ## Turn off blocking 
if( !$rv ) {
    ## Did we succeed or did the call fail?
}