Hi Prasad,
1. The lambdas generated from Class::method, () -> {}, and instance::method are
all from LambdaMetafactory (if you look at the BootstrapMethods attribute from
javap -c -v output), so they always have the same behavior.
2. For JDK 11, according to https://github.com/openjdk/jdk/pull/12493 they were
not strongly tied, but I personally don't know about the details back then.
Chen
________________________________
From: Prasad Velagapudi <[email protected]>
Sent: Wednesday, June 12, 2024 10:35 AM
To: Chen Liang <[email protected]>
Subject: [External] : Re: Lambda Classes reachability from GC roots in JDK11
and JDK17
Thanks Chen for the reply..
Just to clarify, my first question was on the lambda classes loaded from Lambda
expressions(Lexical Lambdas), not the classes created from LambdaMetafactory.
Suppose in this example the line StringFunction ask =
LambdaExpressionsUtil::printLambdaTest; generates a Lambda class. So, I am
curious to know, does this lambda class is STRONGLY tied to defining class
loader in JDK11?
Example1 ::
interface StringFunction {
String print(String str);
}
public class LambdaExpressionsUtil {
public static String printLambdaTest(String str) {
System.out.println(str);
return str;
}
public static void main(String[] args) throws IllegalAccessException,
LambdaConversionException, Throwable {
StringFunction ask = LambdaExpressionsUtil::printLambdaTest;
ask.print("Lambda Expression ask");
}
}
Regards,
Prasad
From: Chen Liang <[email protected]>
Date: Wednesday, 12 June 2024 at 8:52 PM
To: Prasad Velagapudi <[email protected]>
Subject: Re: Lambda Classes reachability from GC roots in JDK11 and JDK17
[External Email]
________________________________
Hello Prasad,
I can confirm the first one is accurate for JDK 15 and later (see JEP 371:
Hidden Classes). Lambda classes from LambdaMetafactory are strongly linked to
the defining class (the lookupClass of the input Lookup) and its class loader,
and is intended to stay this way. Unfortunately I am not sure about the VM,
hope someone can pick up the metaspace part of your question. But I've heard
that since lambda classes are bounded to the lookup class loader, they use less
memory as they don't need to be tracked separately for garbage collection,
-Chen
________________________________
From: core-libs-dev <[email protected]> on behalf of Prasad
Velagapudi <[email protected]>
Sent: Wednesday, June 12, 2024 9:37 AM
To: [email protected] <[email protected]>
Subject: Re: Lambda Classes reachability from GC roots in JDK11 and JDK17
A gentle reminder on these questions… Could you please respond?
Regards,
Prasad.
From: Prasad Velagapudi <[email protected]>
Date: Thursday, 6 June 2024 at 8:10 PM
To: [email protected] <[email protected]>
Subject: Lambda Classes reachability from GC roots in JDK11 and JDK17
Hello Lambda Experts,
I am looking for clarifications on the following questions.
1. I observed in my tests that lambda classes generated for inline lambda
expressions (ex: LambdaUtil::print), are STRONGLY linked to defining class
loader and never gets collected on GC. This behaviour is same in both JDK11 and
JDK17. Can you please confirm is this accurate?
2. Also, I observed that the lambda classes generated for inline lambda
expressions (ex: LambdaUtil::print) not adding additional overhead to Metaspace
in JDK17 compared to that of JDK11 . Can you please confirm is this accurate?
Regards,
Prasad
