RFR: 8199149: Improve the exception message thrown by VarHandle of unsupported operation [v2]

[Mandy Chung]

On Wed, 19 Jul 2023 00:52:49 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Mandy Chung has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   review feedback
>
> src/java.base/share/classes/java/lang/invoke/IndirectVarHandle.java line 93:
> 
>> 91:     @ForceInline
>> 92:     boolean checkAccessModeThenIsDirect(VarHandle.AccessDescriptor ad) {
>> 93:         if (exact && accessModeType(ad.type) != ad.symbolicMethodTypeExact) {
> 
> Can we add a comment that the detailed UOE is thrown via `directTarget.getMethodHandleUncached`?

Actually `VarHandle::checkAccessModeThenIsDirect` can call `isAccessModeSupported` so that this will check properly for `IndirectVarHandle`.

> src/java.base/share/classes/java/lang/invoke/VarHandle.java line 2020:
> 
>> 2018: 
>> 2019:         static AccessMode valueFromOrdinal(int mode) {
>> 2020:             return modeToAccessMode.get(mode);
> 
> Can't this be simplified to `AccessMode.values()[mode]` since this is only rarely used in the exception logic?
> 
> If we do need a cache, I would recommend a stable array like
> 
> private static final @Stable AccessMode[] VALUES = values();
> 
> and users call this accessor instead.
> 
> The code in `getMethodHandleUncached` can benefit from this caching mechanism.

Good suggestion.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14928#discussion_r1267459610
PR Review Comment: https://git.openjdk.org/jdk/pull/14928#discussion_r1267459744