On Mon, 13 Sep 2021 11:06:15 GMT, Сергей Цыпанов <github.com+10835776+stsypa...@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. > Mailing list message from John Rose on core-libs-dev: > > On Sep 13, 2021, at 10:24 AM, Vladimir Ivanov <vlivanov at > openjdk.java.net<mailto:vlivanov at openjdk.java.net>> wrote: > > BTW it can be improved even further by caching the immutable List view of > parameters. > > I would go further: If I were writing MethodType.java today > I would probably use List.of as the backing store for the > parameters, instead of the private array. So ptypes should > be List<Class<?>> not Class<?>[]. I don?t think the footprint > or polymorphism effects would be dealbreakers, and the > code would (I think) be simpler overall. But that?s a messy > change, since the array representation is dug in. Another thing that makes this change hard is that `MethodType` is mapped directly in HotSpot, so that HotSpot can retrieve for instance the parameter types [1]. The VM already knows how to dig into arrays, but adding support for `List` as well seems more cumbersome, since the list internals can change, and AFAIK most VM code can not just call `List::get`. [1] : https://github.com/openjdk/jdk/blob/master/src/hotspot/share/classfile/javaClasses.cpp#L4135-L4137 ------------- PR: https://git.openjdk.java.net/jdk/pull/5489