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can I call a tk fileevent with a delay

by Anonymous Monk
on Sep 12, 2013 at 15:34 UTC ( #1053748=perlquestion: print w/replies, xml ) Need Help??
Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks
How can I change a Tk main window fileevent to go for reading the incoming data every 100ms. Below is my code.
You may even give other small example as well to show this.

use Tk; open(CHILD, "./fileevent2piper 2>&1 |") or die "Can't open: $!"; my $mw = new MainWindow; my $t = $mw->Scrolled("Text",-width => 80, -height => 25, -wrap => 'no +ne'); $t->pack(-expand => 1); $mw->fileevent('CHILD', 'readable', [\&fill_text_widget, $mw]); MainLoop; sub fill_text_widget { my ($widget) = @_; if (eof(CHILD)) { $widget->fileevent('CHILD', "readable", undef); # cancel bindi +ng return ; } else { if (sysread ('CHILD', $_, 128)) { print "here $_ \n"; $t->insert('end', $_); # Append the data read $t->yview('end'); } else { $t->insert('end', times); $t->yview('end'); $widget->fileevent('CHILD', "readable", undef); # cancel b +inding return; } } }

The fileevent2piper code is

$|++; for my $i ( 0 .. 5) { print $i, "\n"; print `ls -la`; sleep 1; }

Replies are listed 'Best First'.
Re: can I call a tk fileevent with a delay
by kcott (Chancellor) on Sep 12, 2013 at 21:14 UTC

    I'd use Tk::after - it has millisecond granularity.

    While I appreciate that the code you posted may well be a highly simplified version of your real application, you may not need Tk::fileevent at all. See my example code where it wasn't needed.

    #!/usr/bin/env perl use strict; use warnings; use Tk; my $mw = MainWindow->new(); my $action_F = $mw->Frame()->pack(-side => 'bottom'); $action_F->Button(-text => 'Exit', -command => sub { exit })->pack; my $text_F = $mw->Frame()->pack(-fill => 'both', -expand => 1); my $ls_T = $text_F->Scrolled('Text', -scrollbars => 'osoe', -wrap => ' +none'); $ls_T->pack(-fill => 'both', -expand => 1); my $out_win = $ls_T; my $tid; my $cmd = 'ls -al 2>&1'; my $repeat = 6; my $delay = 100; $tid = $mw->repeat($delay => [\&update_ls, \$out_win, \$tid, \$cmd, \$ +repeat]); MainLoop; { my $updates = 0; sub update_ls { my ($text_ref, $tid_ref, $cmd_ref, $repeat_ref) = @_; $$text_ref->insert(end => scalar(localtime) . "\n" . qx{$$cmd_ +ref}); if (++$updates >= $$repeat_ref) { my $times_format = '(Usr: %d, Sys: %d, ChUsr: %d, ChSys: % +d)'; $$text_ref->insert(end => sprintf $times_format => times); $$tid_ref->cancel; } $$text_ref->yview('end'); return; } }


    • From Tk::after, I've used the repeat() method to set it up; and the cancel() method when the callback's been called 6 times. [Beyond mirroring the "for my $i ( 0 .. 5) ..." (in your posted code), the 6 is not special.]
    • Notice how all the callback arguments are references. This gives you a lot more flexibility: you could, for instance, change the delay, the command, or even the Tk::Text widget displaying the output.
    • The defaults for -width and -height are 80 and 24, respectively: I've left those two out. I've made the -scrollbars optional (osoe).
    • The code I've posted is complete, working and tested on a directory with 412 entries.

    -- Ken

      Hi Ken,
      Good day!
      The code that you've posted definitely helps me know how to get away with fileevent and handle the problem in a much better and nicer (flexible as everything is passed as reference).

      However, your assumption is right. My code is a much simplified version of my real application. In my application, it is like

      $mainWin->fileevent($socket, 'readable', sub {$self->dataAvailable()} +);
      Here $mainWin is the Tk::MainWindow widget and $socket is a IO::Socket::INET object. I am not sure how can I insert the delay here as it is so easily done by $mw->repeat.
        "I am not sure how can I insert the delay here as it is so easily done by $mw->repeat."

        Here's one way to do it:

        GUI Server (

        #!/usr/bin/env perl use strict; use warnings; use Tk; use IO::Socket; my $mw = MainWindow->new; my $control_F = $mw->Frame()->pack(-side => 'bottom'); my $out_F = $mw->Frame()->pack(-side => 'top', -fill => 'both', -expan +d => 1); my $out_T = $out_F->Scrolled('Text', -scrollbars => 'osoe', -wrap => ' +none'); $out_T->pack(-fill => 'both', -expand => 1); my $out_win = $out_T; my $delay = 100; my ($client, $tid); my @button_pack_opts = (-side => 'left', -padx => 10); $control_F->Button(-text => 'Start Server', -command => [\&start_server, \$client] )->pack(@button_pack_opts); $control_F->Button(-text => 'Start Listening', -command => [\&start_listen, \$mw, \$client, \$tid, \$delay, \$out +_win] )->pack(@button_pack_opts); $control_F->Button(-text => 'Stop Listening', -command => [\&stop_listen, \$out_win, \$tid] )->pack(@button_pack_opts); $control_F->Button(-text => 'Quit', -command => sub { exit } )->pack(@button_pack_opts); MainLoop; sub start_server { my ($client_ref) = @_; my $server = IO::Socket::INET::->new( Proto => 'tcp', LocalPort => 55555, Listen => SOMAXCONN, Reuse => 1 ) or die "Server can't start: $!"; $$client_ref = $server->accept(); $$client_ref->autoflush; return; } sub start_listen { my ($mw_ref, $client_ref, $tid_ref, $delay_ref, $out_ref) = @_; $$tid_ref = $$mw_ref->repeat( $$delay_ref => [\&read_client, $mw_ref, $client_ref, $out_ref] + ); return; } sub stop_listen { my ($out_ref, $tid_ref) = @_; my $times_format = "(Usr: %d, Sys: %d, ChUsr: %d, ChSys: %d)\n"; $$out_ref->insert(end => sprintf $times_format => times); $$out_ref->yview('end'); $$tid_ref->cancel; return; } sub read_client { my ($mw_ref, $client_ref, $out_ref) = @_; $$mw_ref->fileevent($$client_ref, 'readable', sub { if (defined(my $read = readline *$$client_ref)) { $$out_ref->insert(end => $read); $$out_ref->yview('end'); } else { $$mw_ref->fileevent($$client_ref, 'readable', ''); } }); return; }

        Dummy Client (

        #!/usr/bin/env perl use strict; use warnings; use IO::Socket; my $client = IO::Socket::INET::->new( Proto => 'tcp', PeerAddr => 'localhost', PeerPort => 55555 ) or die "Client can't connect: $!"; my $max_iterations = 3; my $sleep_time = 10; for (1 .. $max_iterations) { print $client qx{ls -al 2>&1}; sleep $sleep_time; }


        • Run the GUI Server code and click the Start Server button.
        • Run the Dummy Client code.
        • Go back to the GUI Server and click the Start Listening button: output should appear in the Tk::Text window.
        • You can stop the output with the Stop Listening button. (You can Start/Stop Listening as often as you want.) The repeat() and cancel() methods are in the callbacks for these two buttons.
        • The callback for the repeat event is read_client(). The file event handler is both created and deleted within this subroutine.
        • See perlipc if you have any questions about the Client/Server IO::Socket code: it mostly came from there pretty much unchanged.

        -- Ken

Re: can I call a tk fileevent with a delay
by keszler (Priest) on Sep 12, 2013 at 15:56 UTC

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