Generates bound method handle species classes, and classes with methods that hold compiled lambda form bytecode ahead of time, so certain lambda forms no longer need to spin classes because they can find existing bytecode. Bytecode pre-generation reduces static initialization costs, footprint costs, and circular dependencies that may arise if a class is generated per LambdaForm by InvokerBytecodeGenerator.

Since lambda forms and bound method handle species are closely tied to method types, which have many varieties, this generator needs traces to detect which method types are used, so generation matches the actual usage. See the main entrypoint generateHolderClasses(Stream) for more details about traces.

Note this pregeneration does not cover all lambda forms that can be created. For example, forms created by LambdaFormEditor are not captured.

Pregenerated species classes are resolved in ClassSpecializer.Factory#loadSpecies and behave identically to on-demand generated ones. Pregenerated lambda forms are resolved in InvokerBytecodeGenerator#lookupPregenerated, which looks up methods for code from the following 4 possibly-generated classes:

• Invokers.Holder
• DirectMethodHandle.Holder
• DelegatingMethodHandle.Holder
• LambdaForm.Holder

VarHandle linker forms, analogous to invoker forms in Invokers.Holder, have a similar pre-generation system except it is done at source generation; they reside in VarHandleGuards.

Usages of this generator

Currently, GenerateJLIClassesHelper is invoked when creating a modular JDK image or generating an AOT cache.

Modular Image

When creating a modular JDK image, jdk.tools.jlink.internal.plugins.GenerateJLIClassesPlugin passes the traces in the file jdk/tools/jlink/internal/plugins/default_jli_trace.txt in $JAVA_HOME/lib/modules to this generator. The traces are generated from the execution of build.tools.classlist.HelloClasslist in the build process of the JDK.

To list all the Species classes in a JDK image:

 jimage list $JAVA_HOME/lib/modules | grep BoundMethodHandle.Species_

jimage list $JAVA_HOME/lib/modules | grep BoundMethodHandle.Species_

All these pregenerated classes can be examined by javap in the same image: (Note to escape $ in bash)

 javap -c -p -v java.lang.invoke.LambdaForm\$Holder

javap -c -p -v java.lang.invoke.LambdaForm\$Holder

AOT Cache

When creating an AOT cache, traces generated from the training run are captured and stored inside the AOT configuration file, and are accessed with the C++ FinalImageRecipes class. Classes regenerated from these traces are linked in assembly phase; see regeneratedClasses.hpp.