On Mon, 24 Nov 2025 17:17:37 GMT, Chen Liang <[email protected]> wrote:
>> This is boosting VirtualThread allocations while using >> https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/Thread.Builder.OfVirtual.html#name(java.lang.String,long) >> >> The pattern has been discovered on >> https://github.com/quarkusio/quarkus/issues/51201 and narrowed down in >> https://github.com/franz1981/java-puzzles/commit/5cb4216e8d56cdc6c3c23629419158550cbd9068 >> >> which, on my machine (Ryzen 7950 w fixed frequency at 4.2 GHz): >> >> Benchmark >> Mode Cnt Score Error Units >> VarHandlePolymorphicSignatureSensitivity.rightVarHandle >> avgt 10 1.852 ± 0.007 ns/op >> VarHandlePolymorphicSignatureSensitivity.rightVarHandleConcatIndy >> avgt 10 9.891 ± 0.103 ns/op >> VarHandlePolymorphicSignatureSensitivity.wrongVarHandle >> avgt 10 10.430 ± 0.045 ns/op >> VarHandlePolymorphicSignatureSensitivity.wrongVarHandleConcatIndy >> avgt 10 19.312 ± 0.619 ns/op >> >> where the `right` indy shows: >> <img width="1915" height="469" alt="image" >> src="https://github.com/user-attachments/assets/4c836389-492b-4cc6-94a3-849f8cf6ea09"; >> /> >> >> vs the `wrong` one: >> <img width="1915" height="469" alt="image" >> src="https://github.com/user-attachments/assets/73765060-8e95-42a2-a03a-4f53f927a8b8"; >> /> > > This is not the first time this VarHandle problem is hit - see #16451 > This has bitten me lot of times @liach 😢 Including others while > reading/writing oop fields into arrays too; it would be nice to get an option > to fail fast with an exception enabled via diagnostic args eg > EnableStrictPolymorphicSignature Although Javac should be able to detect it > too, thinking about it twice This can be done using [`VarHandle::withInvokeExactBehavior`](https://docs.oracle.com/en/java/javase/24/docs/api/java.base/java/lang/invoke/VarHandle.html#withInvokeExactBehavior()) on a per var handle basis. C2 can constant fold the type-check away as well. ------------- PR Comment: https://git.openjdk.org/jdk/pull/28475#issuecomment-3572364123
