use strict;
use warnings;

use MCE::Flow;

my $N;

# Workers receive [ begin, end ] values.

MCE::Flow::init(
  max_workers => MCE::Util::get_ncpu(),
  chunk_size  => 100000,
  bounds_only => 1,
  user_begin  => sub { $N = MCE->user_args()->[0] }
);

sub func {
  my ( $beg_seq, $end_seq ) = @{ $_ };
  my ( $pi, $t ) = ( 0.0 );

  for my $i ( $beg_seq .. $end_seq ) {
    $t = ( $i + 0.5 ) / $N;
    $pi += 4.0 / ( 1.0 + $t * $t );
  }

  MCE->gather($pi);
}

# The user_args option is how to pass arguments.
# Workers persist between each run.

for my $e ( 1..8 ) {
  my $n   = 10 ** $e;
  my @ret = mce_flow_s { user_args => [$n] }, \&func, 0, $n - 1;
  my $pi  = 0.0;   $pi += $_ for @ret;

  printf "%9d  %0.14f\n", $n, $pi / $n;
}