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This page describes the command line for the experimental java compiler, the java launcher and HotSpot for the support of value types Minimal Value Types in the valhalla project.

javac

...

Minimal Value Types flags:

 FlagDescription
hotspot  
REQUIRED-XX:EnableMVTBoolean value, default value is `false`

...

If true enable support for minimal value types with a value capable class and an associated derived value type.
REQUIRED-XVerify:noneDisable verification. Verification is not yet supported.
 -XX:ValueArrayFlattenBoolean value, default value is `true`
Flatten arrays of values, if possible
 -XX:ValueArrayElemMaxFlatSizeInteger value, default is -1
Max size for flattening an array of values, < 0 means no limit
 -XX:ValueArrayElemMaxFlatOopsInteger value, default is 4
Max number of embedded object references in value type to flatten in an array, < 0 means no limit 
 -XX:BigValueTypeThreshold

size_t value in bytes, default is 4 * BytesPerLong

Max value type size for interpreter buffering of local variable table entries

 -XX:ValueTypesBufferMaxMemory

Integer value, default 128 (pages)

Max memory used for value type buffers

 -XX:ValueTypesThreadLocalRecycling

Boolean value, default value is 'true'

Enable thread local recycling of buffered values in the interpreter

 -XX:MinimumVTBufferChunkPerFrame

Integer value, default 2

Minimum number of VT buffer chunks allowed per frame

 -XX:ReportVTBufferRecyclingTimes

Boolean value, default false

Print duration of each VTBuffer recycling for the interpreter

 -XX:ValueTypePassFieldsAsArgsNon-product: Boolean value, default value is `true`
Pass each value type field as an argument to a method call instead of a value type reference
 -XX:ValueTypeReturnedAsFieldsNon-product: Boolean value, default value is

...

`true`

...

Return value type

...

fields instead of a value type reference
 -XX:ValueArrayAtomicAccessBoolean value, default value is `false`
Enable atomic access to values in an array, by treating value types as references.
 -XX:-UseTLABTo see heap allocations which do not use optimized Thread Local Allocation Buffers
 -XX:+PrintEliminateAllocationsNon-product builds: Print out when allocations are eliminated
 -XX:+PrintEscapeAnalysisNon-product builds: Print results of escape analysis (e.g. if you believe boxing was not eliminated)
java  
 

...

-Djava.lang.invoke.MethodHandle.DUMP_CLASS_FILES

Boolean value, default value is `false`
If true dump class files generated for lambda forms and derived value types

into a directory named DUMP_CLASS_FILES under the current directory.

 -Dvalhalla.enableValueLambdaForms

Boolean value, default value is `true`
If true then lambda forms with value types in their signature will use the Q type __Value

and value-type specific byte code will be generated.

 -Dvalhalla.dumpProxyClassesBoolean value, default value is `false`
If true, dumps MVT lambda forms.
 -Dvalhalla.enablePoolPatches

Boolean value, default value is `false`
If true and if "valhalla.enableValueLambdaForms" is true then lambda forms with value types in their signature

will generate byte code with constant pool patching where appropriate

...

.

...

javac  
 -Xlint:valuesLint category for warnings associated to bad usage of value capable classes - examples:
  • VCC not final
  • VCC cannot 'extend' another class
  • overrides of 'bad' Object methods (such as wait/notify)
  • illegal modifiers on VCC such as 'synchronized'
  • non-final instance fields in VCC
  • cannot assign 'null' to variable of VCC type

 



 

HotSpot

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