"LW1" - Minimal L-World

LW1 initial prototype is intended to get this into your hands as early as possible so you can provide us with feedback.

Javac source support:

Requires source level >= JDK11
A class declaration may be tagged as being a value type by using the "__ByValue" modifier
- Interfaces, annotation types, enums can not be value types
- Top level, inner, nested, local classes may be value types. Value types may declare inner, nested, local types
- Value Types are implicitly final, so cannot be abstract)
Value Types may not declare an explicit super class. They implicitly extend java.lang.Object akin to enums, annotation types and interfaces
Value Types may declare explicit interfaces
Value Types constructors may not pass the "this" handle until all instance fields are definitely assigned.
All instance fields of a value class are implicitly final
Value types may not to declare fields of its own type directly or indirectly
java.lang.Object methods:
- javac automatically generates hashCode, equals, longHashCode and toString computed solely from the instance's state and not from its identity
- javac does not clone(), finalize(), wait*), notify*() on value receivers
javac does not allow comparison of values using ==, !=
Value Types can not be assigned null, null can not be cast to or compared with value types
Value Types cannot be type arguments in generic type parameterizations, type witnesses in generic method invocations, wildcard bounds
Type migration, including partial recompilation is not supported

Java APIs:

Runtime Exceptions:

Generated class files require ValueTypes attribute, and will throw IncompatibleClassChangeError if value types are used which are not in the attribute
IllegalMonitorException thrown on attempts to synchronize or call wait(*) or notify*() on a value type
ClassCircularityError thrown if loading an instance field of a value type which declares its own type either directly or indirectly

Limitations for LW1

LW1 updates:
- fix bugs, add optimizations and support for additional minor features
LWX:
- Addition of significant feature support
- Addition of language level syntax and semantics
- Eventually a preview with an openjdk release
- Expect specialized generics and support for primitives as value types will have their own early access cycles

Power users - Java/JVM Language, Framework, Library authors/experts
- 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 local repository, based on "lworld" branch:

cd valhalla-lworld

hg defpath du <openjdkname>

hg update -r lw1 // name of branch

To update repository:

cd valhalla-lworld

hg pull

hg update -r lw1 // name of branch

To build repository

bash configure

make images

Note: Valhalla is a child of the jdk/jdk repository, to keep current with latest OpenJDK development.

CMH: Example code

This is intended as an early prototype to give you a chance to experiment and provide feedback on the currently supported features.

Please ensure you are on the latest EA binaries before reporting a problem.

Bugs are tracked in JIRA: Start summary with /[lworld/]. You can search for known problems or already reported bugs.

Use cases that worked for you, including any positive performance or footprint information
Bugs or questions about surprise behavior
Use cases that you would like to see optimized PLEASE

This is intended as an early prototype to give you a chance to experiment and provide feedback on the currently supported features.

At this time it would premature to provide feedback on