This is about Parallel::ForkManager on 64 bit strawberryperl.

I need to process 1000s of images. Each totally independent of the others.

Processing has CPU intensive parts, and parts that hardly use the CPU, but the GPU instead. The hardware has 8 cores, so I think of 8 processes? Each process to start multi-thread programs.

Each image is of different size, and I know the processing time is different according to it. Therefore processes should run a different length.

If a process is finished, a new process should start. To always have 8 processes.

This should level the CPU usage after a few rounds due to the different time each process runs. But it doesn't.

Looking at the Windows 8 Resource Monitor I see that all 8 processes run perfectly synchronized even after a long time.

It looks like 8 process are started, then only after all 8 are finished 8 new processes are started?

Code is straight from: http://search.cpan.org/~szabgab/Parallel-ForkManager-1.06/lib/Parallel/ForkManager.pm

use Parallel::ForkManager;

  ...

  @links=(
    ["http://www.foo.bar/rulez.data","rulez_data.txt"],
    ["http://new.host/more_data.doc","more_data.doc"],
    ...
  );

  ...

  # Max 30 processes for parallel download
  my $pm = Parallel::ForkManager->new(30);

  foreach my $linkarray (@links) {
    $pm->start and next; # do the fork

    my ($link,$fn) = @$linkarray;
    warn "Cannot get $fn from $link"
      if getstore($link,$fn) != RC_OK;

    $pm->finish; # do the exit in the child process
  }
  $pm->wait_all_children;

[download]

In reply to Parallel::ForkManager and CPU usage? by janmartin

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.