RFR: 8199149: Improve the exception message thrown by VarHandle of unsupported operation [v4]

[Jorn Vernee]

On Thu, 20 Jul 2023 15:53:10 GMT, Chen Liang <liach at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/invoke/VarHandle.java line 2010:
>> 
>>> 2008:         static AccessMode valueFromOrdinal(int mode) {
>>> 2009:             return VALUES[mode];
>>> 2010:         }
>> 
>> Also, I'll throw this out there, though I'm not sure how big of an issue it is: this array creation might have an effect on startup. But, since it is only used on a slow path right before we throw an exception (at least, at the moment), calling `values()` every time inside the `valueFromOrdinal` method, and avoiding the array creation on startup, might be 'better'.
>
> I think this is a worthy change: see https://github.com/openjdk/jdk/pull/14943/files#diff-556b309ea2df3f5bfe8229de944183ef19750ce4511d0328cd59af2ce2b61ae2R135
> that `VarHandle.AccessMode.values()` is called every time a polymorphic VH call is linked.
> 
> If the startup cost from array allocation is really problematic, we can make it stable and allocate `VALUES` on demand (at `valueFromOrdinal` calls).

Ah, so it looks like we are creating this array already, in adding the `valueFromOrdinal` method allows sharing. That sounds good!

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/14928#discussion_r1269702376