RFR: 8261407: ReflectionFactory.checkInitted() is not thread-safe [v5]

[Peter Levart]

On Thu, 10 Feb 2022 13:36:11 GMT, liach <duke at openjdk.java.net> wrote:

>> liach has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
>> 
>>  - use peter's model of separate data object
>>  - Merge branch 'master' into 8261407-reflectionfactory
>>  - Include the stable annotation
>>  - Merge branch 'master' into 8261407-reflectionfactory
>>  - Merge branch '8261407-reflectionfactory'
>>  - Just use volatile directly to ensure read order
>>  - 8261407: ReflectionFactory.checkInitted() is not thread-safe
>
> Updated per suggestion of peter and mandy. Requesting another round of review.

Hi @liach ,

This looks good. Maybe we could even make these configuration parameters constant-foldable so they are basically constants if/when JIT compiles the code. 1st, you would have to mark the static `config` field as `@Stable` and move the fast-path check above the check for `VM.isModuleSystemInited()` like this:


    private static @Stable Config config;

    private static Config config() {
        Config c = config;
        if (c != null) {
            return c;
        }
        
        // Defer initialization until module system is initialized so as
        // to avoid inflation and spinning bytecode in unnamed modules
        // during early startup.
        if (!VM.isModuleSystemInited()) {
            return Config.fallback;
        }

        config = c = new Config(true);
        return c;
    }


And that's basically it. The instance final fields in Config class are trusted by VM since they live in trusted package `jdk.internal.reflect` (see: s[rc/hotspot/share/ci/ciField.cpp:227](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/ci/ciField.cpp#L227), so JIT should constant-fold their values when it compiles the code given that VM has probably already initialized the module system by that time and the `config` field has a non-null reference.

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PR: https://git.openjdk.java.net/jdk/pull/6889