Why not work POSIX::RT:Semaphore

[Dima]

This is my simple code

#!/usr/local/bin/perl
use threads;
use threads::shared;
use POSIX::RT::Semaphore;

$sem = POSIX::RT::Semaphore->init(0, 0);

my $pid = fork;
if ( $pid == 0 )
{
$sem->wait;
print "CODE2\n";
exit;
}

print "CODE1\n";
$sem->post;

Why I see only CODE1???
Why after post in parent process semaphore value in child process was't changed?