RFR: 8275775: Add jcmd VM.classes to print details of all classes [v2]

[David Holmes]

On Tue, 18 Jan 2022 02:50:06 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 refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:
> 
>   8275775 Add VM.classes to print details of all classes

Hi,
This seems reasonable in general but a few details to work through - see comments below.
Thanks,
David

src/hotspot/share/oops/instanceKlass.cpp line 2069:

> 2067:   ResourceMark rm;
> 2068:   _st->print("%-18s", "KlassAddr");
> 2069:   _st->print("  ");

Can't you just print the two spaces in the previous line:

_st->print("%-18s  ", "KlassAddr");

and save all the additional print calls. This applies throughout where you have "  ".

src/hotspot/share/oops/instanceKlass.cpp line 2085:

> 2083:   ResourceMark rm;
> 2084:   // klass pointer
> 2085:   _st->print("" INTPTR_FORMAT "", p2i(k));

Why do you need the two empty string literals ??

src/hotspot/share/oops/instanceKlass.cpp line 2100:

> 2098:   char buf[10];
> 2099:   int i = 0;
> 2100:   if (k->has_finalizer()) buf[i++] = 'F';

Where is the meaning of these flags documented?

src/hotspot/share/oops/instanceKlass.cpp line 2103:

> 2101:   if (k->has_final_method()) buf[i++] = 'f';
> 2102:   if (k->has_vanilla_constructor()) buf[i++] = 'V';
> 2103:   if (k->is_instance_klass()) {

Don't the properties queried in L2100 to L2102 only apply to instance classes?

src/hotspot/share/oops/instanceKlass.cpp line 3425:

> 3423: 
> 3424: static const char* state_names[] = {
> 3425:   "alloc", "load", "link", "initing", "inited", "init_err"

I don't like these short forms - they are mostly computerese not real words. Why can't we print the original full names? (Though I'd prefer "initializing" and "initialized" to "being_initialized" and "fully_initialized".)

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

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

s/java/Java/

src/hotspot/share/services/diagnosticCommand.hpp line 873:

> 871:   }
> 872:   static const char* impact() {
> 873:       return "Medium: Depends on Java content.";

I would think impact is High due to the number of classes.

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

Changes requested by dholmes (Reviewer).

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