in reply to Reading non-blockingly / "awk has to be better for something."

Throwing in more detail, the I/O poller module is Gtk2::Helper, whose documentation warns: "you should not use Perl's builtin read and write functions here because these operate always with buffered I/O. Use low level sysread() and syswrite() instead."

I'm not really sure what to construe of that. sysread() needs a size -- should I just read one byte at a time as Grimy suggested above? Am I doing this all wrong by using Perl's buffered I/O? (The code behaves as expected even if I use my current style.)

  • Comment on Re: Reading non-blockingly / "awk has to be better for something."

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Re^2: Reading non-blockingly / "awk has to be better for something."
by james2vegas (Chaplain) on Jul 28, 2012 at 09:48 UTC
    When using Gtk2 I normally use the AnyEvent wrapper over that, especially for its AnyEvent::Handle's methods which let you define reading by line as you wish. But keeping with plain Gtk2 you can just, with your $fh set non-blocking, call sysread with the maximum expected length of your data, like this: 

    use IO::Handle;
my $fh = *STDIN;
$fh->blocking(0);
while (1) {  # this block would go in your callback, not in a loop lik
+e this:
  $fh->sysread( my $data, 255 ); 
  print "$data";   # split $data into lines on CR|LF put the first lin
+e on the end of the last line of the previous block (use an array per
+haps)
}

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      I'm having a bit of trouble going the plain Gtk2 route. I'm not sure what's wrong since I mucked around with the code and changed its behaviour a few times already, but it either 1) works until EOF, after which it goes to an infinite loop, or 2) sysreads the whole output on one go.

        my $cmd = [perl => -e => '$|++; for my $i (0..4) { $sum+= $i; print 
+"Line $i: sum = $sum\r\n"; sleep 1;}'];

  my $cb = sub {print "CB: >>" . shift() . "<<\n";}

  open($fh, '-|', @$cmd) or die "failed to launch external command: $!
+";
  $fh->blocking(0);

  $tag = Gtk2::Helper->add_watch($fh->fileno, in => sub {
    if ($fh->eof) {
      print "pipe EOF\n";
      Gtk2::Helper->remove_watch($tag);
      close $fh;
      return;
    }
    while (1) {
      my $buf;
      $fh->sysread($buf, 4095);
      print "READ: >>$buf<<\n";
      last unless $buf;
      for (split(/[\r\n]/, $buf)) {
        $cb->($_);
      }
    }

    # keep watch active
    return TRUE;
  });

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        Here's a self-contained version of that code.

        Read more... (1253 Bytes)

        It goes into EOF-loop if it says last unless $buf, and into slurp mode if it says return FALSE unless $buf

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Re^2: Reading non-blockingly / "awk has to be better for something."
by Anonymous Monk on Jul 28, 2012 at 09:00 UTC
[reply]

In Section Seekers of Perl Wisdom