Hi Monks, I have a hash I want to pass back from a thread via shared memory. Having done that for many years and quite reliably so with every other data type, this has me a little bit surprised. Note I have left out shared memory access synchronisation calls for simplicity in this example (I coordinate access via semaphores normally). In the code below, I am simply getting a "Magic number checking on storable string failed at /System/Library/Perl/5.18/darwin-thread-multi-2level/Storable.pm line 417, at ./test.pl line 46" error and it won't even run. Can anybody see the problem? 
#!/usr/bin/perl -w
use strict;
use IPC::SysV qw(IPC_PRIVATE S_IRUSR S_IWUSR S_IRWXU IPC_CREAT IPC_EXC
+L);
use IPC::SharedMem;
use Storable qw(freeze thaw);

my %somehash;

$somehash{'one'}{'count'} = 1;
$somehash{'one'}{'string'} = "This is a big ol' string";

use constant {
  STOP => 0,
  RUN => 1
};

my $shm_mastercontrol = IPC::SharedMem->new(IPC_PRIVATE, 8, S_IRWXU);
my $shm_somehash = IPC::SharedMem->new(IPC_PRIVATE, 1024, S_IRWXU);
$shm_mastercontrol->write(pack("S", RUN), 0, 2);

# forks processes
my $thread_PID = fork();
if (not defined $thread_PID) {
  die "Insufficient resources to fork Runner!\n";
} elsif ($thread_PID == 0) {
  &thread();
}

sub thread() {
  #my $string;
  while () {
    # increment the somehash counter:
    $somehash{'one'}{'count'}++;
    print "thread sees: $somehash{'one'}{'count'}\n";
    my $serialized = freeze \%somehash;
    $shm_somehash->write(pack("A*", $serialized), 0, 1024);
    last if ( unpack("S", $shm_mastercontrol->read(0, 2)) == STOP);
    select(undef, undef, undef, 1.0);
  }
  exit(0);
}

while () {
  my $unpacked = unpack("A*", $shm_somehash->read(0, 1024));
  # put somehash back from shared memory:
  %somehash = %{thaw($unpacked)};
  print "main sees: $somehash{'one'}{'count'}\n";
  print "press some key, q to quit:\n";
  chomp (my $key = <STDIN>);

  if ( $key eq 'q' ) {
    $shm_mastercontrol->write(pack("S", STOP), 0, 2);
    waitpid($thread_PID, 0);
    last;
  }
}

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In reply to can't thaw a hash: Magic number error. by balt

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