You can replace:

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

With:

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

Which is more compact, but not easier nor more efficient.

Two possibilities:

1. You can build a normal (non-shared) subhash and when complete, use threads::shared::shared_clone() to make a shared copy of it and assign a reference to the copy to a key/value pair in the main shared hash:

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

2. You can create a shared subhash and assign a ref to it without needing to copy:

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

You'll get better answers if you describe your actual application. Ie. Real requirements garner working responses.

In a subroutine (or anywhere else), you can use unshared variables and/or shared variables as required.