RFR: 8251397: Add release fence to ClassValueMap constructor

[Aleksey Shipilev]

On Wed, 9 Sep 2020 13:04:38 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Updated PR.
>
> Now I wonder (after reading the discussion), why not `UNSAFE.storeStoreFence()`? I am basically okay with either, given
> they currently map to the same thing. But it seems that semantically only `storeStoreFence` is really needed here.

Scratch that. Hotspot does `MemBar_Release` for final stores, low-level Java code is better do the same:
 https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/parse1.cpp#L1005

It deserves a separate follow-up to homogenize the uses of `Unsafe.storeStoreFence` and `Unsafe.storeFence` in other
places in JDK.

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PR: https://git.openjdk.java.net/jdk/pull/94