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State based hashcode for value types #15529

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hangshao0 opened this issue Jul 12, 2022 · 6 comments
Closed

State based hashcode for value types #15529

hangshao0 opened this issue Jul 12, 2022 · 6 comments
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comp:vm project:valhalla Used to track Project Valhalla related work

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@hangshao0
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hangshao0 commented Jul 12, 2022 •
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The hash code of a value type should be based on its state rather than the identity (address).
Currently OpenJ9 still calculates the hash code of value types using its address rather than its value.
@hangshao0 hangshao0 added comp:vm project:valhalla Used to track Project Valhalla related work labels Jul 12, 2022
@hangshao0
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This is related to #15497.

JCL has a private helper in class PrimitiveObjectMethods that calculates the VT hash code:
private static int primitiveObjectHashCode(Object o)

@hangshao0
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@ehrenjulzert will be look at this.

@hangshao0 hangshao0 mentioned this issue Aug 17, 2022
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@hangshao0
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Doing call-in inside existing native method convertValueToHash() is not an option, see the discussions here: #15741.

@ehrenjulzert ehrenjulzert mentioned this issue Aug 22, 2022
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@hangshao0 hangshao0 mentioned this issue Sep 16, 2022
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As we discussed in #15880, implementing hashcodes for value types natively will be difficult and require changes to the GC. It also may not be worth it to sink too too much time into the native implementation since the spec may change in the future to remove the need to hash value types at all. For this reason I've decided to instead make a temporary implementation purely in Java which just calls the primitiveObjectHashCode helper function.

@ehrenjulzert ehrenjulzert mentioned this issue Sep 19, 2022
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ehrenjulzert pushed a commit to ehrenjulzert/openj9 that referenced this issue Sep 22, 2022
Use primitiveObjectHashCode function when hashing value types
754e181 
- Add valueHashCode function to J9VMInternals.java and call
  it from Object.java
- Create new native helper function positiveOnlyHashcodes
  to check if hashcodes are all positive
- Change DDR's hashcode command to display an error when
  trying to get the hashcode of a valuetype

for eclipse-openj9#15529

Signed-off-by: Ehren Julien-Neitzert <[email protected]>
@ehrenjulzert ehrenjulzert mentioned this issue Oct 25, 2022
Merged
ehrenjulzert pushed a commit to ehrenjulzert/openj9 that referenced this issue Oct 27, 2022
Use valueObjectHashCode function when hashing value types
97c372b 
- Add valueHashCode function to J9VMInternals.java and call
  it from Object.java
- Create new native helper function positiveOnlyHashcodes
  to check if hashcodes are all positive
- Change DDR's hashcode command to display an error when
  trying to get the hashcode of a valuetype
- Update java_lang_invoke_MethodHandleNatives.cpp to
  ensure that the MN_FLATTENED flag is set correctly

for eclipse-openj9#15529

Signed-off-by: Ehren Julien-Neitzert <[email protected]>
ehrenjulzert pushed a commit to ehrenjulzert/openj9 that referenced this issue Nov 7, 2022
Add testing for VT hashcodes
4a3bc9e 
Tests code added in PR eclipse-openj9#15922
Part of solution of issue eclipse-openj9#15529

Signed-off-by: Ehren Julien-Neitzert <[email protected]>
@hangshao0
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This can be closed.

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github-actions bot commented Oct 3, 2024

Issue Number: 15529
Status: Closed
Actual Components: comp:vm, project:valhalla
Actual Assignees: No one :(
PR Assignees: ehrenjulzert, ehrenjulzert

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