use strict;
use warnings;

use Inline 'C' => <<'END_C';

  unsigned int N = 0;

  void c_init( unsigned int n )
  {
    N = n;
  }

  double c_func( unsigned int beg_seq, unsigned int end_seq )
  {
    double t, pi = 0.0;
    unsigned int i;

    for ( i = beg_seq ; i <= end_seq ; i++ ) {
      t = (double) i / (double) N;
      pi += 4.0 / ( 1.0 + t * t );
    }

    return pi;
  }

END_C

use MCE::Flow;

# Workers receive [ begin, end ] values.

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

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

  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;
}