in reply to Re^7: Please suggest a non-forking way to do this (OS: windows)
in thread Please suggest a non-forking way to do this (OS: windows)

Why do you say sysread won't block?

This script does it, by adding the O_NONBLOCK flag to the piped open. top is set to give output every 10 secs, yet the Tk gui is still running fine. 

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $mw = MainWindow->new(-background => 'gray50');

my $text = $mw->Scrolled('Text')->pack();

my $pid;
my $startb = $mw->Button( -text => 'Start',
                -command=> \&work,
                 )->pack();

my $count = 0;
my $label = $mw->Label(-textvariable=>\$count)->pack();

my $testtimer = $mw->repeat(500,
                   sub { $count++}  );

my $stopb = $mw->Button( -text => 'Exit',
                -command=>sub{
                 kill 9,$pid;
                 exit;
              },
                 )->pack();

MainLoop;
#####################################

sub work{

$startb->configure(-state=>'disabled');

use Fcntl;
   #long 10 second delay between outputs
  $pid = open (my $fh, "top -b -d 10 |" ) or warn "$!\n";

  fcntl($fh, F_SETFL, O_NONBLOCK) || die "$!\n"; 
# Set the non-block flags  

   my $repeater; 
   $repeater = $mw->repeat(10,
          sub {
                if(my $bytes = sysread( $fh, my $buf, 1024)){;
            $text->insert('end',$buf);    
                $text->see('end');         
          }
      }
     );             
}

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I'm not really a human, but I play one on earth Remember How Lucky You Are

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Re^9: Please suggest a non-forking way to do this (OS: windows)
by ikegami (Patriarch) on Sep 29, 2008 at 21:43 UTC

    Not quite. 

    use strict;
use warnings;

use Fcntl qw( F_SETFL O_NONBLOCK );

my $fh = \*STDIN;
fcntl($fh, F_SETFL, O_NONBLOCK) || die "$!\n"; 
sysread($fh, my $buf, 1);

    [download]
    Your vendor has not defined Fcntl macro F_SETFL, used at ...

    [download]

    Similarly, $fh->blocking(0); is a no-op.

    Like I said earlier, as far as I know, it's impossible to detect whether the pipe has data waiting.

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      as far as I know, it's impossible to detect whether the pipe has data waiting.

      Actually, you can. See PeekNamedPipe() which is explicitly documented as also working on:

      a handle to the read end of an anonymous pipe, as returned by the CreatePipe function.

      Though it is difficult to see how to integrate it with win32/win32sck.c win32_select() in order to allow select to operate in the *nix fashion on pipes as well as sockets?

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]

        Win32API::File has a function that returns the system file handle associated with a Perl file handle, and Win32::API can give access to PeekNamedPipe with minimal fuss.

        Sounds like it's another working solution in this case, even if it can't be integrated with select.

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[select]
      Not quite

      Are you saying the non-blocking script I posted didn't work for you? This slightly modified version using STDIN works fine, in a non-blocking manner for me on linux. Is your error coming on a Windows platform? If thats so, nothing I can do, except encourage people to switch to a real operating system, instead of a game platform. :-)

      Read more... (1494 Bytes)

      s far as I know, it's impossible to detect whether the pipe has data waiting.

      On linux you can, see "perldoc -q waiting".

      I'm not really a human, but I play one on earth Remember How Lucky You Are
[reply]
[d/l]

        This slightly modified version using STDIN works fine, in a non-blocking manner for me on linux.

        I just showed that your fcntl command doesn't work on Windows.

        Is your error coming on a Windows platform? If thats so, nothing I can do, except encourage people to switch to a real operating system, instead of a game platform. :-)

        Windows does have an equivalent to unix's file handles and select (events that can be tied to file handles and WaitForMultipleObjects), but Perl doesn't support them.

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[d/l]
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