On Tue, 6 Sep 2022 16:47:03 GMT, Ioi Lam <ik...@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?
Hi @iklam, is there any additional work I can do on this PR? ------------- PR: https://git.openjdk.org/jdk/pull/10024
