On Fri, 29 Aug 2025 19:17:23 GMT, Chen Liang <[email protected]> wrote:
> java.lang.invoke has a few Holder classes in DirectMethodHandle,
> DelegatingMethodHandle, Invokers, and LambdaForm.
>
> Currently, the comments simply refer to "Placeholder for xxx generated
> ahead-of-time".
>
> However, they carry executed bytecode and show up in flame graphs. The
> current comments are definitely not sufficient for their details and purposes.
>
> To address these shortcomings, I improved the comments on the Holder classes
> and GenerateJLIClassesHelper to briefly describe the generation process. In
> addition, I improved the comments on BoundMethodHandle to provide a more
> efficient overview.
I think it will be useful to describe how the Holder and Species classes are
used to avoid bytecode generation. For example, where do we look up methods
inside Holder? When we do a Class.forName() for a particular Species class?
src/java.base/share/classes/java/lang/invoke/GenerateJLIClassesHelper.java line
61:
> 59: /// which method types are used, so our generation matches the actual
> usage.
> 60: ///
> 61: /// This does not have comprehensive coverage of all lambda forms created
> in a
How about:
`This does not cover all lambda forms created in ...`
src/java.base/share/classes/java/lang/invoke/GenerateJLIClassesHelper.java line
66:
> 64: ///
> 65: /// Currently, `GenerateJLIClassesPlugin` and the AOT process
> pre-generate with
> 66: /// `GenerateJLIClassesHelper`. `GenerateJLIClassesPlugin` runs for JDK
> builds;
How about:
// Currently, `GenerateJLIClassesHelper` is invoked by
`GenerateJLIClassesPlugin` when
// creating a modular JDK image. It it also invoked when generating an AOT
cache.
("Creating a modular JDK image" covers both the case when the JDK is built, or
when you use jlink to create a custom JDK image).
src/java.base/share/classes/java/lang/invoke/GenerateJLIClassesHelper.java line
76:
> 74: /// the classes for linkage in assembly phase; see
> `regeneratedClasses.hpp`.
> 75: ///
> 76: /// VarHandle has a similar pre-generation system for its forms, except
> it is
`[VarHandle]` ?
src/java.base/share/classes/java/lang/invoke/GenerateJLIClassesHelper.java line
356:
> 354: }
> 355:
> 356: /// Returns a map of class name in internal form to the
> corresponding class
`class name` -> `class names`
src/java.base/share/classes/java/lang/invoke/LambdaForm.java line 143:
> 141:
> 142: /// Represents the "basic" types that exist in the JVM linkage and
> stack/locals.
> 143: /// All subwords (boolean, byte, char, short) are promoted to int.
Existing: a few lines below. I think the `// all primitive types` comment
should be deleted.
D_TYPE('D', double.class, Wrapper.DOUBLE, TypeKind.DOUBLE), // all primitive
types
src/java.base/share/classes/java/lang/invoke/LambdaForm.java line 1736:
> 1734:
> 1735: /// Holds pre-generated bytecode for common lambda forms.
> 1736: /// This class may be substituted by a generated class from
> [GenerateJLIClassesHelper].
// This class may be substituted in the JDK's modules image, or in an AOT
cache, by a version
// generated by [GenerateJLIClassesHelper].
src/java.base/share/classes/java/lang/invoke/LambdaForm.java line 1745:
> 1743: /// ```
> 1744: /// javap -c -p -v java.lang.invoke.LambdaForm\$Holder
> 1745: /// ```
Unfortunately, there's currently no way to use `javap` to display the contents
of the re-generated version of the Holder classes in an AOT code. You can use
`-Xlog:aot+map=trace`, but the information is not very easy to parse.
I filed [JDK-8366485](https://bugs.openjdk.org/browse/JDK-8366485) - Display
the contents of generated classes in AOT cache
-------------
PR Comment: https://git.openjdk.org/jdk/pull/27010#issuecomment-3240353292
PR Review Comment: https://git.openjdk.org/jdk/pull/27010#discussion_r2312585502
PR Review Comment: https://git.openjdk.org/jdk/pull/27010#discussion_r2312586114
PR Review Comment: https://git.openjdk.org/jdk/pull/27010#discussion_r2312586845
PR Review Comment: https://git.openjdk.org/jdk/pull/27010#discussion_r2312586972
PR Review Comment: https://git.openjdk.org/jdk/pull/27010#discussion_r2312573559
PR Review Comment: https://git.openjdk.org/jdk/pull/27010#discussion_r2312590553
PR Review Comment: https://git.openjdk.org/jdk/pull/27010#discussion_r2312584042
