RFR: 8078644: CDS needs to support JVMTI CFLH

[Karen Kinnear]

Jiangli,

This looks great! Many thanks. Very creative solution!

Question:

If you load_shared_class for the boot loader and you use the CFLH such that you
return the new_ik, where do you call ClassLoader::add_package?
(I did find a call to notify_class_loaded from fill_instance_klass which is called by create_instance_klass)

thanks,
Karen

p.s. I may have a couple more questions - I will try to get them to you tomorrow. Thanks.

> On Sep 9, 2016, at 11:42 PM, Jiangli Zhou <jiangli.zhou at oracle.com> wrote:
> 
> Here is the updated webrev.
> 
> 	http://cr.openjdk.java.net/~jiangli/8078644/webrev.01/
> 
> Thanks everyone again for the timely feedbacks!
> 
> Jiangli
> 
>> On Sep 9, 2016, at 5:53 PM, Jiangli Zhou <jiangli.zhou at Oracle.COM> wrote:
>> 
>> Hi Dan,
>> 
>> Thanks for the review!
>> 
>>> On Sep 9, 2016, at 3:40 PM, Daniel D. Daugherty <daniel.daugherty at oracle.com> wrote:
>>> 
>>> On 9/6/16 6:14 PM, Jiangli Zhou wrote:
>>>> Hi,
>>>> 
>>>> Please review the following change thats support JVMTI class_file_load_hook(CFLH) during initial loading of shared classes. The webrev also removes the temporary workaround that disables CDS when JVMTI CFLH is required (JDK-8141341 <https://bugs.openjdk.java.net/browse/JDK-8141341>).
>>>> 
>>>> 	webrev:http://cr.openjdk.java.net/~jiangli/8078644/webrev.00/
>>> 
>>> General comment
>>> 
>>> - please make sure all copyright years are updated.
>>> - there are some jcheck space at end-of-line violations
>>> (There are more than what I flagged in the comments below).
>> 
>> Will make sure to fix those before commit.
>> 
>>> 
>>> - I think there might be a data leak with the _cached_class_file
>>> field, but that pre-dates your changes and I have to think about it.
>>> 
>>> 
>>> src/share/vm/oops/instanceKlass.hpp
>>>  No comments.
>>> 
>>> src/share/vm/oops/instanceKlass.cpp
>>>  L2119:   // deallocate the cached class file
>>>  L2120:   if (_cached_class_file != NULL) {
>>>  L2121:     os::free(_cached_class_file);
>>>  L2122:     _cached_class_file = NULL;
>>>  L2123:   }
>>>      Doesn't this use of _cached_class_file need to be checked
>>>      against the shared spaces? I don't think os::free() will
>>>      be happy if _cached_class_file points into shared space.
>> 
>> That’s a good question. Only shared InstanceKlass might have _cached_class_file pointing to shared space. The deallocation call path never happen for shared classes at runtime. So if we get here, we must not be dealing with a shared class and _cached_class_file is not shared. Otherwise we would see issues for other data being freed in InstanceKlass::release_C_heap_structures().
>> 
>>> 
>>> src/share/vm/memory/metaspaceShared.hpp
>>>  No comments.
>>> 
>>> src/share/vm/memory/metaspaceShared.cpp
>>>  No comments.
>>> 
>>> src/share/vm/memory/metaspace.cpp
>>>  No comments.
>>> 
>>> src/share/vm/classfile/klassFactory.hpp
>>>  No comments.
>>> 
>>> src/share/vm/classfile/klassFactory.cpp
>>>  L219:     if ((result->get_cached_class_file()) != NULL) {
>>>  L220:       // JFR might set cached_class_file
>>>  L221:       len = result->get_cached_class_file_len();
>>>  L222:       bytes = result->get_cached_class_file_bytes();
>>>  L223:     } else {
>>>      Perhaps:
>>>            if ((bytes = result->get_cached_class_file()) != NULL) {
>>>              // event based tracing might set cached_class_file
>>>              len = result->get_cached_class_file_len();
>>>            } else {
>>> 
>>>      so two changes:
>>>        - mv init of bytes into the if-statement
>>>        - change 'JFR' -> 'event based tracing’
>> 
>> Updated.
>> 
>>> 
>>> src/share/vm/classfile/systemDictionary.cpp
>>>  No comments.
>>> 
>>> src/share/vm/memory/filemap.hpp
>>>  L260:   }
>>>  L261:   // The estimated optional space size. Only the portion containning data is
>>> 
>>>      Please add a blank line between L260 and L261.
>>> 
>>>      Typo: 'containning' -> ‘containing'
>> 
>> Fixed.
>> 
>>> 
>>>      There's a trailing space on L261; jcheck won't like it.
>> 
>> Fixed.
>> 
>>> 
>>>  L266:   }
>>>  L267:   // Total shared_spaces size includes the ro, rw, md, mc and od spaces
>>> 
>>>      Please add a blank line between L266 and L267.
>> 
>> Done.
>> 
>>> 
>>>  L264:   static size_t optional_space_size() {
>>>  L265:     return core_spaces_size();
>>> 
>>>      It is not clear why core_spaces_size() is being returned as
>>>      an estimate of the optional space size.
>> 
>> Coleen also pointed it out. I added more details.
>> 
>>> 
>>>      There's a trailing space on L265; jcheck won't like it.
>> 
>> Fixed.
>> 
>>> 
>>> src/share/vm/memory/filemap.cpp
>>>  No comments.
>>> 
>>> src/share/vm/utilities/debug.hpp
>>>  No comments.
>>> 
>>> src/share/vm/utilities/debug.cpp
>>>  L289:     "shared miscellaneous code space",
>>>  L290:   };
>>>      The name string for the new space is missing.
>>>      Perhaps "shared optional space"…
>> 
>> Also fixed when incorporating Coleen’s feedbacks. The estimated shared space size should be large enough and never run out space. Added a check.
>> 
>> Thanks!
>> 
>> Jiangli
>> 
>>> 
>>> Dan
>>> 
>>> 
>>>>       bug: JDK-8078644 <https://bugs.openjdk.java.net/browse/JDK-8078644>
>>>> 
>>>> Class file data is needed when posting CFLH. For shared classes, the class file data are now archived at dump time. That avoids re-reading the class file data from the JAR file or reconstituting the data at runtime, which would add class loading overhead for shared classes.
>>>> 
>>>> To minimize the runtime memory overhead, the archived class file data are stored in a separate shared space, called ‘optional data space’ (od).  The ‘od’ space a new region in the archive. It does not increase runtime memory usage when JvmtiExport::should_post_class_file_load_hook() is false. The memory contains the archived class file data is only paged in when the VM needs to post CFLH.  The ‘od’ space can be shared by different processes.
>>>> 
>>>> When loading shared class at runtime, we now call JvmtiExport::post_class_file_load_hook() with the archive class file data if needed. If JVMTI agent modifies the class, new InstanceKlass is created using the modified class data and the archived class is ignored.
>>>> 
>>>> Tested with JPRT, CDS tests and QA tests.
>>>> 
>>>> Thanks,
>>>> Jiangli
>>> 
>> 
>