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perl multithreading

by spx2 (Chaplain)
on May 15, 2007 at 04:47 UTC ( #615459=perlquestion: print w/ replies, xml ) Need Help??
spx2 has asked for the wisdom of the Perl Monks concerning the following question:

hi i want to get a job im required to know perl multithreading i have a hunch that the programming OS will be Windows ofcours i'll be coding in perl. my question is,what is one commonly to know about multithreaded programming in perl,not only on Windows. what should i read. also what small project could i make to use this concept. all suggestions are welcome

Comment on perl multithreading
Re: perl multithreading
by Zaxo (Archbishop) on May 15, 2007 at 04:58 UTC

    One approach is to call fork and rely on the win32 porters to have got the emulation right. See perlport.

    Perl threading is still in a perilous state because the different OS's haven't quite agreed on what threading should act like. POSIX threads have been exposed as inconsistent, iirc.

    After Compline,
    Zaxo

Re: perl multithreading
by chrism01 (Friar) on May 15, 2007 at 06:34 UTC
    Well, here is the std Perl threads tutorial http://perldoc.perl.org/perlthrtut.html .
    And more MS specific http://aspn.activestate.com/ASPN/docs/ActivePerl/5.8/lib/threads.html as you'll prob be using ActiveState Perl.

    I've only ever used it on Linux & Solaris, but it works fine.
    You just have to be careful, especially if you've never used threads before.
    Note that if you want a multi-level variable eg HoH... to be thread shared, you have to explicitly share each level as it's created.
    Something I learnt from BrowserUK.
    Anyway, as usual, feel free to ask qns.
    It's true that officially it's not prod ready as some (or more) modules are not guaranteed 'thread-safe'. However, there are many threaded perl progs running in production.

    Cheers
    Chris

Re: perl multithreading
by Moron (Curate) on May 15, 2007 at 11:23 UTC
    I would try to memorise Chapters 16 & 17 (Interprocess Communication and Threads respectively) in Programming Perl by Larry Wall, Randal L. Schwartz, Tom Christiansen & Stephen Potter.
    __________________________________________________________________________________

    ^M Free your mind!

Re: perl multithreading
by zentara (Archbishop) on May 15, 2007 at 12:06 UTC
    Here is a general purpose example that runs on windows.
    #!/usr/bin/perl use warnings; use strict; use threads; use threads::shared; #works on Windows my $data = shift || 'date'; #sample code to pass to thread my %shash; #share(%shash); #will work only for first level keys my %hash; my %workers; my $numworkers = 3; foreach my $dthread(1..$numworkers){ share ($shash{$dthread}{'go'}); share ($shash{$dthread}{'progress'}); share ($shash{$dthread}{'timekey'}); #actual instance of the thread share ($shash{$dthread}{'frame_open'}); #open or close the frame share ($shash{$dthread}{'handle'}); share ($shash{$dthread}{'data'}); share ($shash{$dthread}{'pid'}); share ($shash{$dthread}{'die'}); $shash{$dthread}{'go'} = 0; $shash{$dthread}{'progress'} = 0; $shash{$dthread}{'timekey'} = 0; $shash{$dthread}{'frame_open'} = 0; $shash{$dthread}{'handle'} = 0; $shash{$dthread}{'data'} = $data; $shash{$dthread}{'pid'} = -1; $shash{$dthread}{'die'} = 0; $hash{$dthread}{'thread'} = threads->new(\&work,$dthread); } use Tk; use Tk::Dialog; my $mw = MainWindow->new(-background => 'gray50'); my $lframe = $mw->Frame( -background => 'gray50',-borderwidth=>10 ) ->pack(-side =>'left' ,-fill=>'y'); my $rframe = $mw->Frame( -background => 'gray50',-borderwidth=>10 ) ->pack(-side =>'right',-fill =>'both' ); my %actives = (); #hash to hold reusable numbered widgets used for d +ownloads my @ready = (); #array to hold markers indicating activity is need +ed #make 3 reusable downloader widget sets------------------------- foreach(1..$numworkers){ push @ready, $_; #frames to hold indicator $actives{$_}{'frame'} = $rframe->Frame( -background => 'gray50' ); $actives{$_}{'stopbut'} = $actives{$_}{'frame'}->Button( -text => "Stop Worker $_", -background => 'lightyellow', -command => sub { } )->pack( -side => 'left', -padx => 10 +); $actives{$_}{'label1'} = $actives{$_}{'frame'} ->Label( -width => 3, -background => 'black', -foreground => 'lightgreen', -textvariable => \$shash{$_}{'progress'}, )->pack( -side => 'left' ); $actives{$_}{'label2'} = $actives{$_}{'frame'} ->Label( -width => 1, -text => '%', -background => 'black', -foreground => 'lightgreen', )->pack( -side => 'left' ); $actives{$_}{'label3'} = $actives{$_}{'frame'} ->Label( -text => '', -background => 'black', -foreground => 'skyblue', )->pack( -side => 'left',-padx =>10 ); } #-------------------------------------------------- my $button = $lframe->Button( -text => 'Get a worker', -background => 'lightgreen', -command => sub { &get_a_worker(time) } )->pack( -side => 'top', -anchor => 'n', -fill=>'x', -pady +=> 20 ); my $text = $rframe->Scrolled("Text", -scrollbars => 'ose', -background => 'black', -foreground => 'lightskyblue', )->pack(-side =>'top', -anchor =>'n'); my $repeat; my $startbut; my $repeaton = 0; $startbut = $lframe->Button( -text => 'Start Test Count', -background => 'hotpink', -command => sub { my $count = 0; $startbut->configure( -state => 'disabled' ); $repeat = $mw->repeat( 100, sub { $count++; $text->insert( 'end', "$count\n" ); $text->see('end'); } ); $repeaton = 1; })->pack( -side => 'top', -fill=>'x', -pady => 20); my $stoptbut = $lframe->Button( -text => 'Stop Count', -command => sub { $repeat->cancel; $repeaton = 0; $startbut->configure( -state => 'normal' ); })->pack( -side => 'top',-anchor => 'n', -fill=>'x', -pady => 20 ) +; my $exitbut = $lframe->Button( -text => 'Exit', -command => sub { foreach my $dthread(keys %hash){ $shash{$dthread}{'die'} = 1; $hash{$dthread}{'thread'}->join } if ($repeaton) { $repeat->cancel } #foreach ( keys %downloads ) { # #$downloads{$_}{'repeater'}->cancel; #} # $mw->destroy; exit; })->pack( -side => 'top',-anchor => 'n', -fill=>'x', -pady => 20 + ); #dialog to get file url--------------------- my $dialog = $mw->Dialog( -background => 'lightyellow', -title => 'Get File', -buttons => [ "OK", "Cancel" ] ); my $hostl = $dialog->add( 'Label', -text => 'Enter File Url', -background => 'lightyellow' )->pack(); my $hostd = $dialog->add( 'Entry', -width => 100, -textvariable => '', -background => 'white' )->pack(); $dialog->bind( '<Any-Enter>' => sub { $hostd->Tk::focus } ); my $message = $mw->Dialog( -background => 'lightyellow', -title => 'ERROR', -buttons => [ "OK" ] ); my $messagel = $message->add( 'Label', -text => ' ', -background => 'hotpink' )->pack(); $mw->repeat(10, sub{ if(scalar @ready == $numworkers){return} foreach my $set(1..$numworkers){ $actives{$set}{'label1'}-> configure(-text =>\$shash{$set}{'progress'}); if(($shash{$set}{'go'} == 0) and ($shash{$set}{'frame_open'} == 1)) { my $timekey = $shash{$set}{'timekey'}; $workers{ $timekey }{'frame'}->packForget; $shash{$set}{'frame_open'} = 0; push @ready, $workers{$timekey}{'setnum'}; if((scalar @ready) == 3) { } $workers{$timekey} = (); delete $workers{$timekey}; } } }); $mw->MainLoop; ################################################################### sub get_a_worker { my $timekey = shift; $hostd->configure( -textvariable => \$data); if ( $dialog->Show() eq 'Cancel' ) { return } #---------------------------------------------- #get an available frameset my $setnum; if($setnum = shift @ready){print "setnum->$setnum\n"} else{ print "no setnum available\n"; return} $workers{$timekey}{'setnum'} = $setnum; $shash{$setnum}{'timekey'} = $timekey; $workers{$timekey}{'frame'} = $actives{$setnum}{'frame'}; $workers{$timekey}{'frame'}->pack(-side =>'bottom', -fill => 'both' ); $workers{$timekey}{'stopbut'} = $actives{$setnum}{'stopbut'}; $workers{$timekey}{'stopbut'}->configure( -command => sub { $workers{$timekey}{'frame'}->packForget; $shash{ $workers{$timekey}{'setnum'} }{'go'} = 0; $shash{ $workers{$timekey}{'setnum'} }{'frame_open'} = 0; push @ready, $workers{$timekey}{'setnum'}; if((scalar @ready) == $numworkers) { } $workers{$timekey} = (); delete $workers{$timekey}; }); $workers{$timekey}{'label1'} = $actives{$setnum}{'label1'}; $workers{$timekey}{'label1'}->configure( -textvariable => \$shash{$setnum}{'progress'}, ); $workers{$timekey}{'label2'} = $actives{$setnum}{'label2'}; $workers{$timekey}{'label3'} = $actives{$setnum}{'label3'}; $workers{$timekey}{'label3'}->configure(-text => $timekey); $shash{$setnum}{'go'} = 1; $shash{$setnum}{'frame_open'} = 1; #--------end of get_file sub-------------------------- } ################################################################## sub work{ my $dthread = shift; $|++; while(1){ if($shash{$dthread}{'die'} == 1){ goto END }; if ( $shash{$dthread}{'go'} == 1 ){ eval( system( $shash{$dthread}{'data'} ) ); foreach my $num (1..100){ $shash{$dthread}{'progress'} = $num; print "\t" x $dthread,"$dthread->$num\n"; select(undef,undef,undef, .5); if($shash{$dthread}{'go'} == 0){last} if($shash{$dthread}{'die'} == 1){ goto END }; } $shash{$dthread}{'go'} = 0; #turn off self before returning }else { sleep 1 } } END: } #####################################################################

    There are a few things to remember about threads and perl. Try to create your threads first, before you invoke any other modules, because the thread gets a copy of the existing process, and you can get problems with cross-thread-interference when using modules that are not thread-safe( most modules are not thread-safe ). Try to contain your modules in the threads, if you use LWP, for instance, declare "use LWP;" within the thread code block. Finally, threads must return or reach the end of their code block before they can be joined or exit without error. It's a common pitfall to watch out for.

    Use the Super-search here at Perlmonks and search for "threads" for many examples.


    I'm not really a human, but I play one on earth. Cogito ergo sum a bum
      At present I am working on GUI. In this I created some icon buttons. And I want to make this buttons multi-threaded. For one of the buttons subroutine I created a thread. The thread is working fine ( i shared the variables, created at begininng). The problem in the threaded subroutine is I am loading a external perl file( for example - do 'add.pl') which is not working ( i mean not loading). The external file also loads other files, modules in itself. What is the problem I am facing here. Is that I have make all the variables in this external file as shared variables?

        You've just responded to a four year old thread. Not a good idea. Instead, compose a new question in the "Seekers of Perl Wisdom" section.

        Before you do that, however, take the time to read How do I post a question effectively? In particular, show us the code you've written and the specific error messages you're seeing.

Re: perl multithreading
by mantra2006 (Hermit) on May 15, 2007 at 13:08 UTC

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