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• 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
  • Arrays of value types are flattened
  • Can contain primitives or references

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How to Try Minimal Value Types:

Early Access Binaries

http://jdk.java.net/valhalla/

Repository and Build Instructions

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hg clone http://hg.openjdk.java.net/valhalla/valhalla valhalla-mvt

cd valhalla

sh get_source.sh

-mvt

hg defpath du <openjdkname> 

hg update -r mvt // name of branchsh common/bin/hgforest.sh update -r mvt

To update repository: 

cd valhalla

sh common/bin/hgforest.sh pull

-mvt

hg pull

hg sh common/bin/hgforest.sh update -r mvt  // name of branch

To build repository

bash configure

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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.

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• 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

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• Code samples
  • See directory jdk/test/valhalla/mvt in your repository
    • e.g. MethodHandlesTest

Run Experimental MVT

• java -Xverify:none -XX:+EnableMVT <Test>
• Command-line flags: Minimal Value Types Command-line Options
• java: use -Xverify:none -XX:+EnableMVT

Filing Bugs

Filing Bugs

• Send email to valhalla-dev@openjdk.java.netFile openjdk bugs with synopsis starting with "[MVT]" and labels: "mvt"

Limitations

• platforms: x64 Linux, x64 Mac OS X
• no verifier VarHandles (work-in-progress for an update)no VarHandles
• 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

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• Experimental Appendix for Java Virtual Machine Specification for Value Classes
• http://cr.openjdk.java.net/~chegar/docs/sandbox.html  // instructions for working with branch repositories

• Minimal Value Types Command-line Options
• Youtube JVMLS 2017: Minimal Value Types: Origins and Programming Model
  
• Youtube JVMLS 2017: Minimal Value Types: Under the Hood
  

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