use strict;
use warnings;

use English qw( -no_match_vars ); # For $CHILD_ERROR
use POSIX ();

my $BATCH_SIZE = 8;

my @commands;

LINE:
while (<DATA>) {
    next LINE if m/^\s*#/;
    chomp;
    my ($txt_file, $tab_file, $total_documents) = split m/,/, $_, 3;
    my $command = "doit $txt_file > $tab_file";
    push @commands, [ $command, $txt_file, $total_documents ];
}

while (@commands) {
    my @pids;
    my %txt_file_by;

    for my $cmd (splice @commands, 0, $BATCH_SIZE) {
        my ($command, $txt_file, $total_documents) = @$cmd;
        my $pid = system(1, $command);
        push @pids, $pid;
        my $timestamp = POSIX::strftime('%H:%M:%S', localtime);
        print "$timestamp\t$pid\t$command\n";
        $txt_file_by{$pid} = $txt_file;
    }

    for my $pid (@pids) {
        $pid == waitpid($pid, 0) or die;
        die if $CHILD_ERROR;
        my $timestamp = POSIX::strftime('%H:%M:%S', localtime);
        print "$timestamp\t$pid\t$txt_file_by{$pid}\n";
    }
}

exit 0;

__DATA__
D000349000.txt,D000349000.tab,564530
Z0000042.txt,Z0000042.tab,457277
Z0000013336.txt,Z0000013336.tab,457277
Z0000013426.txt,Z0000013426.tab,382292
D000250000.txt,D000250000.tab,382014
C000004770.txt,C000004770.tab,356580
Z000003462.txt,Z000003462.tab,356580
Z000004770.txt,Z000004770.tab,356580
Z0000012073.txt,Z0000012073.tab,349325
D000303000.txt,D000303000.tab,347852
Z0000013787.txt,Z0000013787.tab,347852
Z0000014288.txt,Z0000014288.tab,289025
D004607000.txt,D004607000.tab,268763
D000245000.txt,D000245000.tab,258363
Z0000012214.txt,Z0000012214.tab,257861
Z0000013342.txt,Z0000013342.tab,257861
Z0000015322.txt,Z0000015322.tab,243612
D000275000.txt,D000275000.tab,242962
D000272000.txt,D000272000.tab,224791
D000271000.txt,D000271000.tab,223537
D000717000.txt,D000717000.tab,216624
Z0000015315.txt,Z0000015315.tab,215390
D004457000.txt,D004457000.tab,211271
Z0000012004.txt,Z0000012004.tab,211271