RFR: 8227054: ServiceThread needs to know about all OopStorage objects

[Kim Barrett]

> On Aug 20, 2019, at 3:42 PM, coleen.phillimore at oracle.com wrote:
> 
> 
> The iterator code seems to have taken on a life of it's own, but the runtime changes still look good.

Thanks.

> Can you put some comment about why is there a singular iterator and what its purpose is?  Is there some implicit use I can't find?
> 
> +  // Construct a singular iterator.  The only valid operations are
> +  // destruction/copy/assignment.
> +  Iterator() :
> +    _index(singular_index),
> +    _limit(singular_index)
> +    DEBUG_ONLY(COMMA _category(singular)) {}
> +
> 

Does this help?

-  // Construct a singular iterator.  The only valid operations are
-  // destruction/copy/assignment.
+  // Construct a singular iterator, not associated with any of the sets
+  // (strong, weak, or all) of storage objects.  The only valid operations
+  // are destruction/copy/assignment.

Singular iterators exist so you can declare a variable and later assign to it, for example

    Iterator it;
    if (need_strong) {
      it = strong_iterator();
    } else {
      it = weak_iterator();
    }
    … use the iterator …

The C++ standard uses the phrase “iterator with a singular value”; “singular iterator” is
a common shorthand.