I am not sure if I understand correctly what the challenge is. Each child must return back results as a data chunk independent of any other child's. The run_on_finish() sub receives each child's data and, in my example, puts all children's data together in a hash keyed on child pid (see note below about that). Why? because I had assumed that you want to keep separate each child's results, that it is possible that child1 returns data with id=12 and so can child2. If that is not necessary, e.g. if each child returns results which can be added to a larger hash without any of the keys being the same over some children, then fine, it is not set on stone, just merge the children's returned hashes into a larger hash like so:

my %results = ();
$pfm->run_on_finish( sub {
    my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_stru
+cture_reference) = @_;
    my $data = Sereal::Decoder::decode_sereal($$data_structure_referen
+ce);
    # surely this is sequential code here so no need to lock %results,
+ right?
    @results{keys %$data} = values %$data;
});

[download]

This will create a "flatter" hash without pid information but there is the risk of key clashes: if %child1 contains key id=12 and %child2 contains key id=12 (at the top level of their hashes), the new hash %results can contain, of course, only 1 value for it and that will be what is in the last child.

A nested hash is probably more efficient than a flat-out hash of 1 million items. At least as far as possible key collisions are concerned. Other Monks can correct me on that. In general, I would assume that hash with 1 million items is child's play for Perl.

Note on using PIDs as hash keys: Using children's pid as a hash key to collect each child's results is not a good idea because pid numbers can be re-cycled by the OS and two children at different times may get the same pid. A better idea is to assign each child its own unique id drawn from a pool of unique ids and given to the child at fork just like its input data.

Let me know if I got something wrong or you have more questions

bw, bliako

In reply to Re^3: Parallel::ForkManager and multiple datasets by bliako
in thread Parallel::ForkManager and multiple datasets by Speed_Freak

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.