RFR: 8264032: Improve thread safety of Runtime.version()

[Andrey Turbanov]

On Tue, 23 Feb 2021 16:59:45 GMT, liach <github.com+7806504+liach at openjdk.org> wrote:

>>>This shouldn't be a problem.
>> 
>> What do you mean by "this"? Double racy read?
>> There are 2 separate reads of fields. First can return non-null value, while second still can get `null`
>
>> There are 2 separate reads of fields. First can return non-null value, while second still can get null
> 
> Can this really happen? If this `version` field has been updated, its value is definitely no longer `null`. And before the second field read the field is always set to a non-null value on the current thread. I fail to understand why the second read can still yield a null given the fact that the current thread has updated it to a non-null value and other threads may have updated it to a non-null value.

I'm not really a JMM mastermind, but I know that @shipilev knows a thing or two about it :)
See https://shipilev.net/blog/2016/close-encounters-of-jmm-kind/#wishful-benign-is-resilient

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PR: https://git.openjdk.java.net/jdk/pull/2691