RFR: 8273656: Improve java.lang.invoke.MethodType.parameterList() and its usage

[Jorn Vernee]

On Mon, 13 Sep 2021 11:06:15 GMT, Сергей Цыпанов <github.com+10835776+stsypanov at openjdk.org> wrote:

> Currently the method is implemented like
> 
> public List<Class<?>> parameterList() {
>   return Collections.unmodifiableList(Arrays.asList(ptypes.clone()));
> }
> 
> This seems to be excessive, as three objects are allocated here. Instead we can use `List.of(ptypes)` which doesn't allocate anything for empty array and for one of length 1 and 2 it allocates lightweight objects with 2 fields, still copying longer arrays. This is likely to be fruitful as most of methods have 0-2 parameters.
> 
> Also there is a couple of cases when `MethodType.parameterLis()` is called to get its size, which is excessive either as we can use `MethodType.parameterCount()` instead.

The null-hostile-ness of `contains` is not something I thought about. It would have been good to mention that in the PR body as well. FWIW, I did a search on grep.app for `parameterList()` calls in java [1] and don't really see any calls to `contains`.

I think process-wise creating a CSR would be good, and shouldn't be too much work. Though, I'm not familiar with the process of filing a CSR after a patch has already been merged.

[1] : https://grep.app/search?q=.parameterList%28%29&filter[lang][0]=Java

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PR: https://git.openjdk.java.net/jdk/pull/5489