Minimal Value Types Minimal Value Types OpenJDK Wiki (original) (raw)

Welcome to the Minimal Value Types early adopter's project !

What is the Minimal Value Types (MVT) project?

The Minimal Value Types project is an early prototype for Value Types
- provides initial subset of Value Type functionality
- provides a new type which is:
  * immutable, identity-agnostic, non-nullable, non-synchronizable, final
  * does not inherit from java.lang.Object
- Value Types contained in References, other Value Types or in Arrays are flattenable
- Value Types can contain primitives or references

Power users - Java/JVM Language, Framework, Library authors/exports
- who are comfortable with early experimental software
- who recognize that everything in the experiment - the model, the classfile extensions, the byte codes is likely to change
- who want to contribute to early exploration of Value Types
- who will not build any products based on these prototypes
Who are willing to provide feedback to the developers on a subset of Value Type features
Who will provide use cases for the development team to experiment with optimizations

To create a new mvt branch:

cd valhalla-mvt

hg defpath du

hg update -r mvt // name of branch

To update repository:

cd valhalla-mvt

hg pull

hg update -r mvt // name of branch

To build repository

bash configure

make images

http://cr.openjdk.java.net/~chegar/docs/sandbox.html // instructions for working with branch repositories (not yet updated for consolidation)

Note: Valhalla is a child of the jdk10/hs repository, to keep current with latest hotspot development.

Create a POJO using an experimental javac, with an annotation ValueCapableClass (jvm.internal.value.ValueCapableClass)
- JVM will derive a Derived Value Class (DVC) from this defined "box" which we call the Value Capable Class (VCC)
- DVC contains an immutable copy of the instance fields from the VCC
Work with MethodHandles and experimental reflection package ValueType (jdk.experimental.value.ValueType)
Or spin your own byte codes
- experimental MethodBuilder (jdk/experimental/value.MethodHandleBuilder)
- future: ASM support is planned
Code samples
- See directory jdk/test/valhalla/mvt in your repository
  * e.g. MethodHandlesTest

platforms: x64 Linux, x64 Mac OS X
no VarHandles (work-in-progress for an update)
no support for atomic fields containing value types (work-in-progress for an update)
no JNI, unsafe, jvmti, redefineclasses, reflection
-Xint and C2 only, no C1, no tiered-compilation
interpreter is not optimized, focus is on JIT optimization
Need additional USE CASES for optimizations
Working on additional test cases