RFR: 8271513: support JavaThreadIteratorWithHandle replacement by new ThreadsList::Iterator [v2]

[David Holmes]

On Mon, 2 Aug 2021 11:13:54 GMT, Kim Barrett <kbarrett at openjdk.org> wrote:

>> src/hotspot/share/runtime/threadSMR.hpp line 331:
>> 
>>> 329:   }
>>> 330: 
>>> 331:   using Iterator = ThreadsList::Iterator;
>> 
>> Is this like a typedef? I don't think I want to see plain "Iterator" and not know what the actual type is here.
>
> It's a type alias, which in this simple form is just like a typedef.  Type aliases can also have template parameters.  The iterator type used for iterating over a ThreadsListHandle today happens to be the same type as used for iterating over the underlying ThreadsList.  There's no particular reason to wire that information in to clients.

So `ThreadsListHandle::Iterator` is a global(?) alias for `ThreadsList::Iterator`?

If find this name/type aliasing somewhat obscure and confusing. I mean ideally the thing returned would just be an `Iterator` and the details of whether it is a `Foo::Iterator` or `Bar::Iterator` would not be evident in the API.

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PR: https://git.openjdk.java.net/jdk/pull/4948