RFR(s): 8244733: Add ResourceHashtable::xxx_if_absent (was: ResourceHashtable::compute_if_absent)

[Thomas Stüfe]

Hi all.

new version:
http://cr.openjdk.java.net/~stuefe/webrevs/8244733--add-resourcehashtable--compute_if_absent/webrev.02/webrev/

with Coleens feedback worked in:

I removed the compute_if_absent() variant since of the new three methods it
seems the least useful one; this leaves us with a variant which
default-creates the value if not found, and one with puts a caller provided
value if not found. I also removed the default argument for the p_created
output.

As per Coleen's request, I named the methods both "put_if_absent". See
comments at the method; I hope the intent is still clear.

I also fixed up the callers and the test.

Thanks, Thomas



On Thu, May 14, 2020 at 10:08 AM Thomas Stüfe <thomas.stuefe at gmail.com>
wrote:

> Hi,
>
> This is a continuation of the review thread:
> https://mail.openjdk.java.net/pipermail/hotspot-runtime-dev/2020-May/039444.html
>
> I changed the title of the bug somewhat hence the new thread.
>
> JBS: https://bugs.openjdk.java.net/browse/JDK-8244733
> Webrev:
> http://cr.openjdk.java.net/~stuefe/webrevs/8244733--add-resourcehashtable--compute_if_absent/webrev.01/webrev/
>
> This now adds three new functions to ResourceHashTable:
>
> new_if_absent(), compute_if_absent(), put_if_absent()
>
> which work very similar to their equivalents in j.u.Map.
>
> The advantage they offer is that for a typical "if map does not contain X,
> add X+value" pattern we only do the lookup once.
>
> --
>
> So I extended the scope of the item. After playing around with various
> call sites I realized that David's proposal of put_if_absent() would be
> useful, as well as a variant which just adds a default constructed value.
> All three are tested in gtest and used in real call sites.
>
> Ran tests tonight in our CI, all went through.
>
> Thanks, Thomas
>
>
>