if( exists $copyRef->{ $step } ) {
                 $copyRef = $copyRef->{ $step };
             }
             else {
                 lock %{ $copyRef };
                 $copyRef = $copyRef->{ $step } = &share( {} );
             }

##</code><code>##

            lock %{ $copyRef };
            $copyRef = $copyRef->{ $step } //= &share( {} )

##</code><code>##

...
my %subhash;
... # populate it
lock %mainSharedHash;
$mainSharedHash{ $key } = shared_clone( \%subhash );
...

##</code><code>##

...
my %subhash :shared:
... # populate it
lock %mainSharedHash;
$mainSharedHash{ $key } = \%subhash;