RFR: 8260366: ExtendedSocketOptions <clinit> can deadlock in some circumstances [v2]

[Andrey Turbanov]

On Thu, 18 Feb 2021 07:35:51 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

>> Yes. Once here and once inside `synchronized` block.
>> Reading `volatile` fields cost _something_ on some architectures, so I think we could optimize it a bit.
>
> Hello @turbanoff, the double read is necessary to correctly avoid any race conditions and is a typical strategy used in cases like these. I am not aware of any other alternate more performant strategy, for code like this.

Let me be more clear: I think that it's enough to have only 2 `volatile` field reads _in worst case_. We can use local variable to avoid more than needed reads.
Current code can perform read 4 times _in worst case_: twice outside `synchronized` block and twice inside `synchronized` block.

There are many examples of similar code in the JDK:
https://github.com/openjdk/jdk/blob/master/src/jdk.crypto.cryptoki/share/classes/sun/security/pkcs11/P11Util.java#L48
https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/StackFrameInfo.java#L125

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PR: https://git.openjdk.java.net/jdk/pull/2601