symgryph has asked for the wisdom of the Perl Monks concerning the following question:

I have some code that essentailly runs a bash script sequentially, and was trying to multiprocess the managed children of the program. Aka, I use perl to run program x on y # of files. I use it as an orchestrator. When I try to run on multiple files, I get two running processes with the same filename, instead of two processes running on two different filenames. I am not sure on how to make my code multi-process aware, and need some help. Here is my code. 
#!/usr/bin/env perl -w
use Parallel::ForkManager;
my $filename = 'all.txt';
my $failuresfilename="failed.tsv";
open (my $target, "<", $filename) or die "Cannot open < $filename: $!"
+;
open (my $failures, ">", $failuresfilename) or die "Cannot open > $fai
+luresfilename: $!";
sub readinFile {
  @lines = <$target>;
}
sub execute {
  $multiprocess = Parallel::ForkManager->new(2);
  TARGETS:
  foreach $processme (@lines) {
    $multiprocess->start and next TARGETS;
    
    chomp $processme;
    $command="cfn_nag_scan -o json --input-path $processme > $processm
+e_.cfnag.json";
    `$command`;
     $multiprocess->finish;
  }
}
sub findFailures {
  @files=`find ./ -iname "*cfnag*"`;
  $jqcommand='jq --raw-output \'.[] | select (.file_results.failure_co
+unt > 0) |[.filename, .file_results.failure_count] |@tsv\'';
  foreach (@files) {
    chomp;
    s/\/\//\//g;
    @a=`cat $_ |$jqcommand`;
    print $failures @a;
  }
}
readinFile();
execute();
#findFailures();
close $failures;
close $failuresfilename;

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The subroutine in question is 'execute'. Any help would be appreciated. My input is a bunch of filenames that come from the 'find' command (in this case things I want to scan with cfn_nag). The system sub-executes cfn_nag_scan from the filenames array, which in turn system's the cfn_nag which outputs a bunch of 'scan' result files. Perl is more of a dispatcher than a processor of data.
"Two Wheels good, Four wheels bad."
  • Comment on Using Parallel::ForkManager on multiple files using backtick operators for multiple files being processed simulnaneously
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Re: Using Parallel::ForkManager on multiple files using backtick operators for multiple files being processed simulnaneously
by 1nickt (Canon) on Feb 19, 2020 at 19:18 UTC

    Hi, you didn't supply sample input or output, or describe what the external program does, so the following is untested, but here's something to try using MCE. 

    #!/usr/bin/env perl -w

use strict;
use warnings;
use MCE::Loop;
use Capture::Tiny 'capture_stdout';
use Text::CSV 'csv';
use Try::Tiny;
use JSON;

MCE::Loop::init { max_workers => 8, use_slurpio => 1 };

my $data_filename = 'all.txt';
my $fail_filename = 'failed.tsv';

my $cmd = 'cfn_nag_scan';
my @args = qw/ -o json --input-path /;

my @results = mce_loop_f {
    my ($mce, $slurp_ref, $chunk_id) = @_;
    my @failures;
    while ( $$slurp_ref =~ /([^\n]+\n)/mg ) {
        my $line = $1;
        my $json = try {
             return decode_json(capture_stdout { system($cmd, @args, $
+line) });
        }
        catch {
            warn "processing $line failed: $_";
            return;
        };

        next unless $json;

        my $failure_count = $json->{file_results}{failure_count};
        push @failures, [ $json->{filename} => $failure_count ] if $fa
+ilure_count;
    }
 
    # Gather results 
    MCE->gather(@failures); 
} $data_filename;

unshift @results, [qw/ Filename Failures /];
csv (in => \@results, out => $fail_filename, sep_char=> "\t");

__END__

    [download]

    update: added json decoding and exception handling; changed return to next (thx marioroy)

    Hope this helps!


    The way forward always starts with a minimal test.
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Re: Using Parallel::ForkManager on multiple files using backtick operators for multiple files being processed simulnaneously
by jo37 (Curate) on Feb 19, 2020 at 19:25 UTC

    Always use strict;. This would tell you that $processme_ is not declared. So at least your output file is the same for all processes named ".cfnag.json".

    -jo

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      The simpler solution was to just cat the filenames to a file, and then process with gnu parallel.
      "Two Wheels good, Four wheels bad."
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