push @{ $parent->{children} }, $child;
weaken( $child->{parent} = $parent );   # Needed to avoid memory leak.

##</code><code>##

{
   Resource res = get_resource_exclusively(res_id);
   // ...
   res.release();  // Needed or the next line might fail.
}

{
   Resource res = get_resource_exclusively(res_id);
   // ...
   res.release();
}

##</code><code>##

Resource res = get_resource_exclusively(res_id);
try {
   // ...
}
catch (Exception e) {
   res.release();
   throw e;
}