RFR: 8301119: Support for GB18030-2022 [v2]

[Claes Redestad]

On Thu, 23 Feb 2023 08:32:29 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> `Charset` class is initialized *before* system properties are set up, in order to check the JNU encoding (used for file path name) is a supported charset or not. In some OS environments, GB18030 is the native encoding so we need to avoid checking the system property in such a case.
>
> `@Stable` semantics are still fuzzy to me but the rule I've adhered to is that back to back stores to the field - if unavoidable - needs to be idempotent since the JIT (or AOT) may record any non-null value as a compile time constant at any time.
> 
> I'd write this to not update the static field if initLevel() < 1. Such calls should be rare and only happen once on a system that has GB18030 as their native encoding.

Scratch that: as it seems to be important that we don't switch after startup then what this code is really reaching for is `static final` field semantics. Since `StandardCharsets` might be loaded very early a holder class pattern might be necessary:


    isGB18030_2000() { return GB18030Properties.GB18030_2000; }

    private static class GB18030Properties {
        private static final GB18030_2000 = init();
        private static boolean init() {
            if (VM.initLevel() < 1) {
                // Cannot get the system property yet. Assumes non-2000
                return false;
            }
            return "2000".equals(GetPropertyAction.privilegedGetProperty("jdk.charset.GB18030"));
        }
    }

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PR: https://git.openjdk.org/jdk/pull/12518