After another peek, I find a few other fields in Class can benefit from @Stable too: classData, packageName, allPermDomain, reflectionFactory, classValueMap. They are all accessed with benign race.
There are other fields I'm interested in promoting to @Stable, most notably enumConstants and enumConstantsDirectory; they use mutable data structures and need extra release/store (LoadStore+StoreStore) fences. In addition, I am not sure if Class redefinition would tamper these fields. Thus, I am also CC'ing serviceability-dev for a confirmation. Same question applies to genericInfo field, which is not protected as part of ReflectionData (that explicitly supports JVMTI redefinitions) somehow. Curious, Chen On Tue, Dec 19, 2023 at 7:38 AM - <liangchenb...@gmail.com> wrote: > Thanks for the analysis. I know that in a race, VM is free to promote any > non-null value to a constant. Thus using @Stable is totally safe; > similarly, the reflectionFactory is @Stable and created with a benign race. > I'll create an RFE then. > > > On Tue, Dec 19, 2023, 3:40 AM Jaikiran Pai <jai.forums2...@gmail.com> > wrote: > >> Hello Chen, >> >> Looking at the implementation of java.lang.Class.getName(), which then >> triggers the hotspot code to initialize this "name" field, I suspect there >> will be a (harmless) race in the hotspot implementation where more than one >> thread could end up writing the "name" field (with the same value of >> course) >> https://github.com/openjdk/jdk/blob/master/src/hotspot/share/classfile/javaClasses.cpp#L1237. >> I don't know how the JVM would then react if such a field is marked @Stable >> (the javadoc of @Stable states that the behaviour is such cases is >> undefined). >> >> -Jaikiran >> On 16/12/23 8:37 pm, - wrote: >> >> Hello, >> I just noticed the Class.name field is mutable but not @Stable, meaning >> `Class.getName()` calls are not eligible for constant folding. >> >> The last update to this field is in 2019 in JDK-8216302 when the field >> initialization was done directly by a write from hotspot code (for the >> class name is interned anyways, though interning limits scalability of >> hidden classes) >> >> Would it be a good idea to submit a patch to mark this field @Stable? >> Given class names may be frequently used to quickly identify a class, to >> create descriptors. >> >> Chen Liang >> >>
