Presumably there is a delay before the data response to write() is available from read(). Here is how to wait and also time out after a certain delay so you don't go infinite. The read_data() sub will return a value 3 seconds after the program starts. This simulates a delay. It will time out as shown as we only try to get data for 2 seconds. Uncomment the $wait = 5; line to see it succeed. You can see that it tries a lot (several hundred times) - this is very resource intensive so a short sleep is often a good idea before retries. You can trial the sleep 1 to see it cut the retries. There is a Time::HiRes module available to let you sleep a few millisconds which would generally be better as a full second is a bit over the top as you note. 

$wait = 2;  # wait up to this many seconds for data
# $wait = 5;
$start = time();

# zero our vars and then enter the do until loop
$timeout = $wait + time();
$data = '';
$count = 0;
do { 
    $count++;
    $data = read_data();
    # sleep 1 unless $data;
} until $data or time() > $timeout;

if ($data) {
    print "Tried $count times\nGot data '$data'\n";
} else {
    print "Tried to read_data() but failed after $wait seconds and $co
+unt tries!\n";
}

# a short sub that only returns data after 3 seconds from
# program start time
sub read_data {
  return (time() > ( $start + 3) ) ? "You have waited long enough!" : 
+'';
}

[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

In reply to Re: read does not block by tachyon
in thread read does not block by Monky Python

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