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  4. Minimal Value Types
  5. Minimal Value Types Command-line Options

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changes.mady.by.user Karen Kinnear

Saved on Aug 09, 2017

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changes.mady.by.user Karen Kinnear

Saved on Aug 09, 2017

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 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

...

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