On Thu, 3 Mar 2022 14:30:34 GMT, Claes Redestad <redes...@openjdk.org> wrote:
> This is also only a partial solution, since the initial array is created and > injected by the VM on a "root" Constructor/Method, see for example the code > for new method: > > https://github.com/openjdk/jdk/blob/5c187e34a58769a129a0aae9e4937907c9060202/src/hotspot/share/runtime/reflection.cpp#L778 > > Depending on usage pattern most of the Constructor/Method objects created are > such root objects (often created in bulk), and only those exposed to user > code via a copy will benefit from this particular enhancement. Which might be > a good optimization when getting the same Constructor/Method from the same > class over and over. > > * Can we skip the `.clone()` when propagating these from a root object to > one we'll expose? We have internal `getShared...` methods for that purpose. > > * If we update the JVM code to inject a reference to > `Class.EMPTY_CLASS_ARRAY` and we can skip the `.clone()`ing as per above we > should see a decent benefit overall. I did also wonder to myself off-list if this style of optimization would be better handled in the JVM were the arrays of arguments are created. If so, I wouldn't feel comfortable implementing that in HotSpot sources myself. > src/java.base/share/classes/java/lang/reflect/Executable.java line 59: > >> 57: >> 58: @SuppressWarnings({"rawtypes"}) >> 59: static final TypeVariable[] NO_TYPE_VARS = new TypeVariable[0]; > > Since you asked me offline about some startup noise from this patch I took a > look. This line might be another small contributor, since it means we're > loading `jlr.TypeVariable` on JVM bootstrap. It would be nice if we could > move this to `TypeVariable`, but we don't support private/package-private > interface fields for some reason. Shouldn't we though, now that we have > private interface fields, etc..? IIRC, Java language-level private interface fields are on the to-do list, but are not a high priority. > src/java.base/share/classes/java/lang/reflect/Executable.java line 61: > >> 59: static final TypeVariable[] NO_TYPE_VARS = new TypeVariable[0]; >> 60: >> 61: static final Class<?>[] NO_TYPES = new Class<?>[0]; > > Less concerning since it doesn't add extra classloading, but I note that we > have similar constants in a few places, including > `j.l.Class.EMPTY_CLASS_ARRAY` and `j.l.r.ProxyGenerator.EMPTY_CLASS_ARRAY`. > Perhaps would make sense to consolidate these into a single place/instance > (and use consistent names) A consolidated location like a non-instantiable java.lang.reflect.EmptyHolder class with static fields? (Exact name subject to bike shedding.) ------------- PR: https://git.openjdk.java.net/jdk/pull/7667
