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Think about Loose Coupling

Re^2: Parallel Computation

by BrowserUk (Pope)
on Nov 17, 2010 at 06:47 UTC ( #871937=note: print w/replies, xml ) Need Help??

in reply to Re: Parallel Computation
in thread Parallel Computation

I'd like to see a demonstration of that?

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Re^3: Parallel Computation
by chrestomanci (Priest) on Nov 18, 2010 at 10:15 UTC

    Here is a skeleton of what you want.

    #!/usr/bin/perl use Parallel::ForkManager; my $max_threads = 5; my $fork_mgr = new Parallel::ForkManager($max_threads); $fork_mgr->run_on_finish ( sub { my($child_pid, $exit_code, $child_id, $exit_signal, $core_dump +) = @_; # Code to store the results from each thread go here. } ); foreach my $item (@big_list) { $fork_mgr->start($url_ent) and next URL # Code in this block will run in parallel my $result = do_stuff($item); # Store the final result. The value you pass to finish will be # received by the sub you defined in run_on_finish $fork_mgr->finish($result); } $fork_mgr->wait_all_children(); # Now all child threads have finished, # your results should be available.

    A few extra tips:

    If you are running this code in the perl debugger, then you might want to debug the child threads. If so, run your program in a unix/linux xterm window. The debugger will create new xterm windows for each child thread, so you can separately step through the parent and the children

    Conversely, if you don't want to step through the children, and your screen is filling up with windows from child threads, you can use the debug option: o inhibit_exit=0 To suppress the display of windows for child threads that finish without hitting a breakpoint.</c>

      Since I'm not the OP, it's unlikely I'm looking to get my homework solved. But then, it's unlikely any teacher would give the OP's problem as homework.

      Thanks for the sample code, but I already know how to use Parallel::ForkManager, I've done so many times.

      What I was seeking is an example of using that module to solve the OPs particular problem. You see, I cannot work out how it would pass back the result and carry from adding the first, rightmost, two digits back to the parent process so that the carry can be passed to the next child when adding the next two digits? Any thoughts?

      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.

        I apologise

        The value passed to $fork_mgr->start() can be used to uniquely identify the thread, and it comes back as $child_id in the subroutine defined in $fork_mgr->run_on_finish()

        Given that ID, you can reconcile the work done by the worker threads. In the past I have used that ID for an array index into the array of work to be done, A string that uniquely identifies the work, or the primary key of a database row.

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[Corion]: haukex: Yes - I see the benefit of using Dist::Zilla for people with 150+ modules on CPAN, but I don't see it for myself, and I'm always put off from contributing to such modules because they require a lot of toolchain setup that I don't want to ...
[Corion]: ... spend time on if I only want to provide a short patch
[haukex]: Corion: Yes exactly, in the author tests I don't worry about portability as much, I also don't list the author tests' dependencies in Makefile.PL
[haukex]: I figure someone who wants to contribute will know how to install the missing modules ;-) Not the nicest way to go but I don't think many people are using my modules yet
[ambrus]: Corion: some of these stupid syntax highlighters assume that too. just look at the table in http://perldoc. functions/pack. html for example.
[haukex]: ..."yet" ;-) I haven't had to deal with Dist::Zilla yet but I've heard about how it's a big setup

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