This would be a problem, however. Since there is currently no official way of defining a class, and since Java agents do not control the class loading order, if a class was loaded for the first time, you could for example not add a field with a type of an auxiliary class that you had planned to inject. A class being loaded is normally the first opportunity for a Java agent and if no witness class is available at this point, using a method handle is no option. Since it is difficult to know if such a witness class is available in the general case, it would also add quite a performance and managerial toll on agent authors. I would hope that an API equally convenient to today's unsafe options could be added.
Am Fr., 16. Apr. 2021 um 18:35 Uhr schrieb <fo...@univ-mlv.fr>: > > > ------------------------------ > > *De: *"Rafael Winterhalter" <rafael....@gmail.com> > *À: *"Remi Forax" <fo...@univ-mlv.fr> > *Cc: *"Rafael Winterhalter" <winterhal...@openjdk.java.net>, > "core-libs-dev" <core-libs-dev@openjdk.java.net>, "serviceability-dev" < > serviceability-...@openjdk.java.net> > *Envoyé: *Vendredi 16 Avril 2021 18:27:46 > *Objet: *Re: RFR: 8200559: Java agents doing instrumentation need a means > to define auxilary classes > > Not by my understanding. A suitable lookup requires a loaded class for the > package. A Java agent might however not provide a handle for a class that > is not yet loaded. Or how would you suggest to approach this ? > > > yes, you need a witness class in the package you want to define a new > class. > Apart if you load classes in the unamed module, you can not load a class > in a non existing package anyway (apart if you generate your own > module-info), > so you need at least a dummy class to define a package, so you can use it > to get a Lookup. > > Rémi > > > > Am Fr., 16. Apr. 2021 um 16:21 Uhr schrieb Remi Forax <fo...@univ-mlv.fr>: > >> ----- Mail original ----- >> > De: "Rafael Winterhalter" <winterhal...@openjdk.java.net> >> > À: "core-libs-dev" <core-libs-dev@openjdk.java.net>, >> "serviceability-dev" <serviceability-...@openjdk.java.net> >> > Envoyé: Vendredi 16 Avril 2021 15:52:07 >> > Objet: RFR: 8200559: Java agents doing instrumentation need a means to >> define auxilary classes >> >> > To allow agents the definition of auxiliary classes, an API is needed >> to allow >> > this. Currently, this is often achieved by using `sun.misc.Unsafe` or >> > `jdk.internal.misc.Unsafe` ever since the `defineClass` method was >> removed from >> > `sun.misc.Unsafe`. >> >> You can already use Lookup.defineClass() + privateLookupIn() + >> Instrumentation.redefineModule() for that ? >> >> Rémi >> >> > >> > ------------- >> > >> > Commit messages: >> > - 8200559: Java agents doing instrumentation need a means to define >> auxiliary >> > classes >> > >> > Changes: https://git.openjdk.java.net/jdk/pull/3546/files >> > Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3546&range=00 >> > Issue: https://bugs.openjdk.java.net/browse/JDK-8200559 >> > Stats: 185 lines in 4 files changed: 185 ins; 0 del; 0 mod >> > Patch: https://git.openjdk.java.net/jdk/pull/3546.diff >> > Fetch: git fetch https://git.openjdk.java.net/jdk >> pull/3546/head:pull/3546 >> > >> > PR: https://git.openjdk.java.net/jdk/pull/3546 >> > >
