RFR: 8275775: Add jcmd VM.classes to print details of all classes [v5]

[Ioi Lam]

On Thu, 20 Jan 2022 09:47:31 GMT, Yi Yang <yyang at openjdk.org> wrote:

>> Add VM.classes to print details of all classes, output looks like:
>> 
>> 1. jcmd VM.classes
>> 
>> KlassAddr Size State Flags LoaderName ClassName
>> 0x0000000800c0b400 62 inited W bootstrap java.lang.invoke.LambdaForm$MH/0x0000000800c0b400
>> 0x0000000800c0b000 62 inited W bootstrap java.lang.invoke.LambdaForm$DMH/0x0000000800c0b000
>> 0x0000000800c0ac00 62 inited W bootstrap java.lang.invoke.LambdaForm$MH/0x0000000800c0ac00
>> ...
>> 
>> 2. jcmd VM.classes verbose
>> 
>> KlassAddr Size State Flags LoaderName ClassName
>> 0x0000000800c0b400 62 inited W bootstrap java.lang.invoke.LambdaForm$MH/0x0000000800c0b400
>> java.lang.invoke.LambdaForm$MH/0x0000000800c0b400 {0x0000000800c0b400}
>>  - instance size: 2
>>  - klass size: 62
>>  - access: final synchronized
>>  - state: inited
>>  - name: 'java/lang/invoke/LambdaForm$MH+0x0000000800c0b400'
>>  - super: 'java/lang/Object'
>>  - sub:
>>  - arrays: NULL
>>  - methods: Array<T>(0x00007f620841f210)
>>  - method ordering: Array<T>(0x0000000800a7e5a8)
>>  - default_methods: Array<T>(0x0000000000000000)
>>  - local interfaces: Array<T>(0x00000008005af748)
>>  - trans. interfaces: Array<T>(0x00000008005af748)
>>  - constants: constant pool [41] {0x00007f620841f030} for 'java/lang/invoke/LambdaForm$MH+0x0000000800c0b400' cache=0x00007f620841f380
>>  - class loader data: loader data: 0x00007f61c804a690 of 'bootstrap' has a class holder
>>  - source file: 'LambdaForm$MH'
>>  - class annotations: Array<T>(0x0000000000000000)
>>  - class type annotations: Array<T>(0x0000000000000000)
>>  - field annotations: Array<T>(0x0000000000000000)
>>  - field type annotations: Array<T>(0x0000000000000000)
>>  - inner classes: Array<T>(0x00000008005af6d8)
>>  - nest members: Array<T>(0x00000008005af6d8)
>>  - permitted subclasses: Array<T>(0x00000008005af6d8)
>>  - java mirror: a 'java/lang/Class'{0x000000011f4b3968} = 'java/lang/invoke/LambdaForm$MH+0x0000000800c0b400'
>>  - vtable length 5 (start addr: 0x0000000800c0b5b8)
>>  - itable length 2 (start addr: 0x0000000800c0b5e0)
>>  - ---- static fields (1 words):
>>  - static final '_D_0' 'Ljava/lang/invoke/LambdaForm;' @112
>>  - ---- non-static fields (0 words):
>>  - non-static oop maps:
>> 0x0000000800c0b000 62 inited W bootstrap java.lang.invoke.LambdaForm$DMH/0x0000000800c0b000
>> java.lang.invoke.LambdaForm$DMH/0x0000000800c0b000 {0x0000000800c0b000}
>>  - instance size: 2
>>  - klass size: 62
>>  - access: final synchronized
>>  - state: inited
>>  - name: 'java/lang/invoke/LambdaForm$DMH+0x0000000800c0b000'
>>  - super: 'java/lang/Object'
>>  - sub:
>>  - arrays: NULL
>>  - methods: Array<T>(0x00007f620841ea68)
>>  - method ordering: Array<T>(0x0000000800a7e5a8)
>>  - default_methods: Array<T>(0x0000000000000000)
>>  - local interfaces: Array<T>(0x00000008005af748)
>>  - trans. interfaces: Array<T>(0x00000008005af748)
>>  - constants: constant pool [49] {0x00007f620841e838} for 'java/lang/invoke/LambdaForm$DMH+0x0000000800c0b000' cache=0x00007f620841ebe0
>>  - class loader data: loader data: 0x00007f61c804a750 of 'bootstrap' has a class holder
>>  - source file: 'LambdaForm$DMH'
>>  - class annotations: Array<T>(0x0000000000000000)
>>  - class type annotations: Array<T>(0x0000000000000000)
>>  - field annotations: Array<T>(0x0000000000000000)
>>  - field type annotations: Array<T>(0x0000000000000000)
>>  - inner classes: Array<T>(0x00000008005af6d8)
>>  - nest members: Array<T>(0x00000008005af6d8)
>>  - permitted subclasses: Array<T>(0x00000008005af6d8)
>>  - java mirror: a 'java/lang/Class'{0x000000011f4b0968} = 'java/lang/invoke/LambdaForm$DMH+0x0000000800c0b000'
>>  - vtable length 5 (start addr: 0x0000000800c0b1b8)
>>  - itable length 2 (start addr: 0x0000000800c0b1e0)
>>  - ---- static fields (1 words):
>>  - static final '_D_0' 'Ljava/lang/invoke/LambdaForm;' @112
>>  - ---- non-static fields (0 words):
>> ...
>
> Yi Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix test

This looks generally OK to me. Some minor suggestions.

src/hotspot/share/oops/instanceKlass.cpp line 2106:

> 2104:   // classloader name
> 2105:   ClassLoaderData* cld = k->class_loader_data();
> 2106:   _st->print("%-12s  ", cld->loader_name());

For custom class loaders, this will likely print a long class name that will over the 12 character limit, making the output somewhat hard to read.



const char* ClassLoaderData::loader_name() const {
   if (_class_loader_klass == NULL) {
     return BOOTSTRAP_LOADER_NAME;
   } else if (_name != NULL) {
     return _name->as_C_string();
   } else {
     return _class_loader_klass->external_name();
   }
}


Also, for custom loaders, printing out just the name of the loader class is not sufficient, as multiple loader instances may have the same type.

Maybe we should just remove line 2106? If the user wants to know the class loader, they can use the "-verbose" option of this jcmd.

src/hotspot/share/services/diagnosticCommand.hpp line 870:

> 868:   }
> 869:   static const char* description() {
> 870:     return "Prints list of all loaded classes";

I think it's better to say "Print all loaded classes". Most commands in this file do not use the third-person singular verb ending. The words "list of" are redundant.

test/hotspot/jtreg/runtime/CommandLine/PrintClasses.java line 40:

> 38:     var pid = Long.toString(ProcessHandle.current().pid());
> 39:     var pb = new ProcessBuilder();
> 40:     pb.command(new String[] { JDKToolFinder.getJDKTool("jcmd"), pid, "VM.classes", "-verbose"});

For sanity, I think we should have two test cases, one with -verbose, and one without.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7105