At last some code to play with - thanks as I do not know where to start with Tk! Unfortunately it still blocks if the external process blocks, for example: sleep 10 && echo hello instead of find.

I have modified your code to non-block with some help from PM's Re: Non blocking read on a filehandle. There is a simpler way though: change the filehandle to O_NONBLOCK after you open it using Fcntl::fcntl(). It does work but it reports weird file flags and I am unsure whether it is safe (Edit: I mean safe to be used with filehandles open'ed to external commands using -| . I think it's OK but this is the warning I get, notice that the reported $flags contain the command's output! Argument "\0sy^F>V\0\0\0\0\0\0\0\0\0\0output\0\0\0\0\0\0\0\0\0\0\0..." isn't numeric in bitwise or (|) Edit2Problem solved: I was reading an older example of fcntl, it should be: my $flags = fcntl($in, F_GETFL, 0) - for non-windows OSes.). Both versions below

# non-blocking pipe using select
use Tk;

{   my $in;
    sub stop { undef $in }

    # modified by bliako
    # non-blocking way to check if $fh has output ready

    sub has_output_ready {
      my ($fh, $nbytes) = @_;
      my $timeout = 0;
      my $rin = '';
      vec($rin, fileno($fh), 1) = 1;
      if( select($rin, undef, undef, $timeout) ){
        my ($buffer);
        read ($fh, $buffer, $nbytes);
        # fh has data and we are returning nbytes max
        # make $nbytes arbitrarily large or next time (if buffer holds
+)
        return $buffer;
      }
      return; # no output at this time, return undef
    }

    sub run {
        my ($type, $entry) = @_;
        my $command = $entry->cget('-text');
        if (1 == $type) {
            my $out = $_[2];
            open $in, '-|', $command or die $!;
            my $repeat;
            $repeat = ($entry->repeat(1, sub {
                return $entry->afterCancel($repeat)
                    if $repeat && ! defined $in;

        # modified by bliako: read blocks,
        # use has_output_ready() instead
                #read $in, my $buff, 100;
        my $buff = has_output_ready($in, 100, 0);
                if ($buff && length $buff) { # undef means no data yet
                    $out->insert(end => $buff);
                    $out->yview('end');
                }
            }));
        } elsif (2 == $type) {
            system "$command&";
        }
    }
}

...

[download]

Second method, using Fcntl::fcntl()

# non-blocking pipe using O_NONBLOCK file flag, unsafe(?)

  ...
  open $in, '-|', $command or die $!;
# modified by bliako to set the filehandle to non-block IO
use Fcntl;
# EDIT: commented below is not supported and outputs warning about ORi
+ng non-numerical flags
#my $flags = "";
#fcntl($in, F_GETFL, $flags) or die "failed to get flags, $!";
# use this instead:
my $flags = fcntl($in, F_GETFL, 0);
# reporting weird flags (linux)!
print "FLAGS: '$flags'\n";
$flags |= O_NONBLOCK;
fcntl($in, F_SETFL, $flags) or die "Couldn't set file flags: $!\n";
...
# and now read is non-block,
# undef will be returned if no output ready
read $in, my $buff, 100;
if ($buff && length $buff) { # check if undef
  ...
}
...

[download]

bw, bliako

In reply to Re^2: Second background process is pausing the gui by bliako
in thread Second background process is pausing the gui by Ohad

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