#!/usr/bin/perl
# this script will take data from shmem
use warnings;
use strict;
use IPC::SysV qw(IPC_STAT IPC_NOWAIT);
use IPC::Msg;

#see "perldoc perlfunc /shmget" and "perldoc perlipc /SysV" 

my $IPC_KEY = 1234;
my $msg = new IPC::Msg($IPC_KEY,0);
#my $msg = new IPC::Msg($IPC_KEY, 1);

print "msg->$msg\n";

my $go = 1;

#get shmid from msg 
my $segment_id;
$msg->rcv($segment_id, 8 , 0); # 8 bytes for a Perl integer 
print "shmid->$segment_id\n"; 

$SIG{INT} = sub{ $go = 0; exit;};
						  
my $segment_size = &size_m($segment_id);
print "segment_size = $segment_size\n";

while($go){
my $readm = &read_m();
print "$readm\n";
last if ! $go;
select(undef,undef,undef,.1);
}
#############################################################

sub size_m(){
  my $segment_id = shift;
  my $shmbuffer = '';
  shmctl ($segment_id, IPC_STAT, $shmbuffer);
  my @mdata = unpack("i*",$shmbuffer);  #not sure if that is right unpack? works :-) 
  print "segment size: ", $mdata[9], "\n";
  return($mdata[9]);
}

#################################################################3

sub read_m(){
   my $buff;
   #the $buff is paaded with nulls \0 to fill it out
   shmread($segment_id, $buff, 0, $segment_size) || die "$!";
   # the buffer of shmread is zero-character end-padded.
   #substr($buff, index($buff, "\0")) = '';
  return ($buff); 
}
__END__