On Thu, 25 Aug 2022 14:32:06 GMT, Strahinja Stanojevic <d...@openjdk.org> wrote:
> This PR introduces a system property that creates stable names for the lambda > classes in the JDK. Instead of using an atomic counter in the lambda name, we > can use a 32-bit hash after `$$Lambda$`. Thus, the name becomes > `lambdaCapturingClass$$Lambda$hashValue`. > Parameters used to create a stable part of the name (hash value) are a > superset of the parameters used for lambda class archiving when the CDS > dumping option is enabled. During the stable name creation process, > all the common parameters are in the same form as in the low-level > implementation (C part of the code) of the archiving process. > We concatenate all of those parameters in one string `hashData`. We calculate > the long hash value for `hashData` in the same manner as the > `java.lang.StringUTF16#hashCode` does, and then we hash that value using > `Long.toString(longHashValue, Character.MAX_RADIX)`. The desired length for > this hash is equal to the length of the `Long.toString(Long.MAX_VALUE, > Character.MAX_RADIX)`. > Sometimes, the calculated hash value is shorter than the desired length, so > we pad it with the character `#` to hit it. Appending `#` only affects the > hash length, but not its stability. > > Link to the related issue: https://bugs.openjdk.org/browse/JDK-8292914 Have you tested with method references? Two references to the same method will result in a single `JVM_CONSTANT_InvokeDynamic` constant pool entry in the classfile, but it's invoked by two callsites. As a result, two different lambda proxy classes will be generated, as the JVMS requires the invokedynamic resolution to be per callsite, not per constantpool entry. public class ShareBSM { public static void main(String args[]) { doit1(ShareBSM::func); doit2(ShareBSM::func); } static void func() { Thread.dumpStack(); } static void doit1(Runnable r) { r.run(); } static void doit2(Runnable r) { r.run(); } } Here's the output: $ java -cp . -XX:+UnlockDiagnosticVMOptions -XX:+ShowHiddenFrames ShareBSM java.lang.Exception: Stack trace at java.base/java.lang.Thread.dumpStack(Thread.java:1380) at ShareBSM.func(ShareBSM.java:8) at ShareBSM$$Lambda$1/0x0000000800c009f0.run(Unknown Source) at ShareBSM.doit1(ShareBSM.java:12) at ShareBSM.main(ShareBSM.java:3) java.lang.Exception: Stack trace at java.base/java.lang.Thread.dumpStack(Thread.java:1380) at ShareBSM.func(ShareBSM.java:8) at ShareBSM$$Lambda$2/0x0000000800c00bf8.run(Unknown Source) at ShareBSM.doit2(ShareBSM.java:15) at ShareBSM.main(ShareBSM.java:4) Will you patch generate the same name for both callsites? Does this matter for your use case? ------------- PR: https://git.openjdk.org/jdk/pull/10024
