#!/usr/bin/perl

use warnings;
use strict;

use IPC::SysV qw(IPC_CREAT ftok SEM_UNDO);
use IPC::Semaphore;

my $semtok = ftok($0,1);
my $shmtok = ftok($0,2);

my $sem = IPC::Semaphore->new($semtok, 1, 0700 | IPC_CREAT)
  or die "Couldn't create semaphore: $!\n";
my $shmid = shmget($shmtok,4,0700 | IPC_CREAT)
  or die "Couldn't create shm: $!\n";

if ($ENV{RESET})
{
  $sem->setval(0,0);
  my $buf = pack("L",0);

  shmwrite($shmid, $buf, 0, 4)
    or die "shmwrite failed: $!\n";
  if (!$ARGV[0])
  {
    exit(0);
  }
}


foreach my $i(1..$ARGV[0]||100)
{
  my $r = add(1);
  if ($ENV{VERBOSE})
  {
    print $r,"\n";
  }
}

sub add
{
  my($add) = @_;
  # Lock: wait for 0, then semaphore up
  $sem->op(0, 0, 0,
           0, 1, 0)
    or die "semaphore lock failed: $!\n";

  # Read counter
  my $buf;
  shmread($shmid, $buf, 0, 4)
    or die "shmread failed: $!\n";
  my $val = unpack("L",$buf);
  # Increment
  $val += $add;
  # Write it back
  $buf = pack("L",$val);
  shmwrite($shmid, $buf, 0, 4)
    or die "shmwrite failed: $!\n";

  # Now unlock; semaphore down
  $sem->op(0, -1, 0)
    or die "semaphore unlock failed: $!\n";

  return $val;
}