RFR: 8044107 Add Diagnostic Command to list all ClassLoaders

[Coleen Phillimore]

On 5/28/14, 3:49 PM, Christian Thalinger wrote:
> On May 28, 2014, at 12:46 PM, Staffan Larsen <staffan.larsen at oracle.com> wrote:
>
>> On 28 maj 2014, at 21:39, Christian Thalinger <christian.thalinger at oracle.com> wrote:
>>
>>> On May 28, 2014, at 7:50 AM, Staffan Larsen <staffan.larsen at oracle.com> wrote:
>>>
>>>> This change adds a new Diagnostic Command to list all ClassLoaders and some statistics for each classloader. The command is called “GC.classloader_stats” and the information listed is:
>>>>
>>>> * An id for the ClassLoader. This is the pointer to the Klass of the ClassLoader. The reason for using the Klass* (instead of the oop) is that it is stable across invocations.
>>>> * The id of the ClassLoader’s parent ClassLoader.
>>>> * The pointer to the ClassLoaderData structure in the VM. This can be useful for debugging.
>>>> * The number of classes loaded by the ClassLoader.
>>>> * The total size of all allocated metaspace chunks for the ClassLoader.
>>>> * The total size of all allocated metaspace blocks for the ClassLoader.
>>>>
>>>> If there are anonymous classes (invokedynamic classes) attributed to the ClassLoader, the following additional information is listed:
>>>> * The number of anonymous classes loaded by the ClassLoader.
>>>> * The total size of all allocated metaspace chunks for anonymous classes in the ClassLoader.
>>>> * The total size of all allocated metaspace blocks for anonymous classes in the ClassLoader.
>>>>
>>>> The information is gathered during a safe point to guarantee that the data structures are consistent.
>>>>
>>>> I have added a small test and have run this through jprt. A CCC request has been filed.
>>>>
>>>> webrev: http://cr.openjdk.java.net/~sla/8044107/webrev.00/
>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8044107
>>>>
>>>> Example output:
>>>>
>>>> ClassLoader         Parent              CLData*            Classes   ChunkSz   BlockSz Type
>>>> 0x00000007c002d908  0x0000000000000000  0x0000000000000000       0         0         0 sun.misc.Launcher$ExtClassLoader
>>>> 0x0000000000000000  0x0000000000000000  0x00007fb239c08de0     761   4694016   4241312 <boot classloader>
>>>>                                                               37     75776     50928   + invokedynamic classes
>>> You shouldn’t name these “invokedynamic classes”; they can be used for different purposes. “anonymous classes” is the correct name.
>> Hmm, yeah. Not a good name, I know. The problem with “anonymous classes” is that for a Java developer, that term is already taken and means something completely different. This is very unfortunate and creates a lot of confusion. My first version called them “lambdas”, but that was even more wrong. Better names are welcome!
> These classes are defined via:
>
>      public native Class<?> defineAnonymousClass(Class<?> hostClass, byte[] data, Object[] cpPatches);
>
> so this is what they are called.  Sorry :-)

It's still a bad name.  I call them jsr292-anonymous classes.  maybe 
"unsafe anonymous classes" ?

Coleen
>
>> /Staffan
>>
>>>> 0x00000007c0061028  0x00000007c0036878  0x00007fb239c2de60       1      6144      1976 ClassLoaderStatsTest$DummyClassLoader
>>>>                                                                1      2048      1288   + invokedynamic classes
>>>> 0x00000007c0036878  0x00000007c002d908  0x00007fb239e10fc0       8     88064     31544 sun.misc.Launcher$AppClassLoader
>>>> Total = 4                                                      808   4866048   4327048
>>>> ChunkSz: Total size of all allocated metaspace chunks
>>>> BlockSz: Total size of all allocated metaspace blocks (each chunk has several blocks)
>>>>
>>>>
>>>> Thanks,
>>>> /Staffan