It turns out the problem has to do with the restriction that you should share scalar variables, not complex structures like hashes. So the parent can see the child's hash modifications if you do something like this:

use forks;
use forks::shared;
my %GLOBALHASH : shared;
my %hashref    : shared;
$hashref = \%GLOBALHASH;


$child = fork ();
if (!$child) {      # child 
    $hashref->{OILPRICE} = 100; exit 0;
} elsif ($child)  {  # daddy
    sleep (2);
    print "Global Oils Price is now: " . $hashref->{OILPRICE} . " doll
+ars\n";
}
[download]

However, I've not been able to get this to work with hashes of hashes.

No, for me, it worked with a hash as well. The restriction applies to threads::shared, not forks::shared.

The restriction applies to threads::shared,

Could you:

1. explain "the restriction"
2. either show where that restriction is documented; or code to demonstrate it?

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