http://qs1969.pair.com?node_id=285432


in reply to returning from a thread ?

...the difference between a thread and a process...

If you're using Perl threads, you shouldn't have to worry about whether it is actually implemented using processes or real threads™. That's why they're "Perl threads".

Having said that, to my knowledge, Linux is the only system where you can actually think of threads as processes, as having seperate program id's (pid's, $$). This allows modules as Thread::Signal to function in that environment. Win32 only knows about real threads and mimics fork() using threads. Other *nixes are somewhere inbetween. Some can fork() and have real threads (Solaris seems to fall in that group). But e.g. on Mac OS X (and presumably other BSD's), threads look as seperate processes, but can not be signalled.

...never-ending sub (ie it's got a while (1) loop)m how can I stop it nevertheless?

Use a shared variable in the while. So: 

while (1) {

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becomes: 
while ($sharedvar) {

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and reset the shared variable in another thread when you want to have the thread in question stop.

In that respect, you might also want to have a look at Thread::Queue::Monitored and/or Thread::Conveyor::Monitored.

Hope this helps.

Liz

Update:
I forgot one other way to do this. This will only work if you are running under Linux for now. Use Thread::Signal to activate a handler that will do a Thread::Exit. No nice cleanup that way, but definitely effective ;-)

Replies are listed 'Best First'.
Re: Re: returning from a thread ?
by Foggy Bottoms (Monk) on Aug 21, 2003 at 14:03 UTC
    I didn't manage to use the shared variable "thinggie" - as I don't have the shared package and since I didn't find it on the ActiveState repository...
    Instead I used a file in which I'm writing a byte (0 for inactive 1 for active)( I know you're thinking it's way too slow but it works fine anyhow...)

    However when the new thread starts up, it blocks the main program and I can't do anything else.
    I know someone already posted a node about this but I can't seem to find it anymore (bad luck :~/ )
    If you've any idea, let me know, and thanks again for your help...
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      Strange. Which version of Perl are you using on which platform? The main program should not block!

      Liz

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        Here's my bit of code below :
           # now stop the current scan thread
   # to do this, write in a file th_com.thd the value 0
   if (defined $thread)
   {
      open (THREADCOM, ">".LTG::dialog::THREADCOM) or die "Can't creat
+e/overwrite file: $!\n";
      print (THREADCOM,"0");
      close THREADCOM;
      # stop thread
   }
   print "create thread\n";
   $thread = threads->new(\&LTG::scanChange::monitor());# \&LTG::scanC
+hange::monitor);
   $thread->detach(); # let go off the new thread

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        And here's the sub's code 
        sub monitor
{
   my @wantedF; # folders to be scanned
   my @bannedF; # banned folders not to be scanned
   
   if ( -e LTG::dialog::CONFIGFILE)
   {
      open(FOLDERLIST,LTG::dialog::CONFIGFILE) or die "can't open file
+";
      my $content = <FOLDERLIST>;
      my $addForce = 0;
      while ($content)
      {        
        if ($content ne "\n")
        {
           $content =~ s/\n/ /;
           ($content =~/^\#FORCE\#/)?($addForce = 1):(($content =~/^\#
+BAN\#/)?($addForce = 0):($addForce?push(@wantedF,$content):push(@bann
+edF,$content)));
        }
        $content = <FOLDERLIST>;
        
      }
      close (FOLDERLIST);
   }
   
   open (THREADCOM, ">".LTG::dialog::THREADCOM) or die "Can't create/o
+verwrite file: $!\n";
   print THREADCOM "1";
   close THREADCOM;
   
   my $active = 1;
   while ($active)
   {
      if ( -e LTG::dialog::THREADCOM)
      {
         open(THREADCOM,LTG::dialog::THREADCOM) or die "can't open fil
+e THREADCOM";
         $active = <THREADCOM>;
         print "active : $active \n";
         close THREADCOM;
      }
      my %changes = LTG::scanChange::startScan(\@wantedF,\@bannedF,INC
+_SUBDIRS);
      foreach my $k (keys %changes)
      {
         print "key : $k -> content : $changes{$k}\n";
      }
      # update database here Sumith
      # print "---while---\n";
   
   }
}

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        I'm running perl on a Winnt 4.0 system, and here's my perl info (perl -v)
        This is perl, v5.6.1 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2001, Larry Wall

Binary build 635 provided by ActiveState Corp. http://www.ActiveState.
+com
Built 15:34:21 Feb  4 2003


Perl may be copied only under the terms of either the Artistic License
+ or the
GNU General Public License, which may be found in the Perl 5 source ki
+t.

Complete documentation for Perl, including FAQ lists, should be found 
+on
this system using `man perl' or `perldoc perl'.  If you have access to
+ the
Internet, point your browser at http://www.perl.com/, the Perl Home Pa
+ge.

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[d/l]
[select]
      Not slow, just ugly.. Very, very ugly..
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