RFR: 8078644: CDS needs to support JVMTI CFLH

[Jiangli Zhou]

Hi Karen,

Thank you so much for the review!

> On Sep 12, 2016, at 1:58 PM, Karen Kinnear <karen.kinnear at oracle.com> wrote:
> 
> 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)

Good catch!! In ClassLoader::load_class(), the add_packege() is done through ClassLoaderExt::Context::record_result(). For shared classes, SystemDictionary::load_shared_class() calls add_package() explicitly for boot loader:

    // For boot loader, ensure that GetSystemPackage knows that a class in this
    // package was loaded.
    if (class_loader.is_null()) {
      int path_index = ik->shared_classpath_index();
      ResourceMark rm;
      ClassLoader::add_package(ik->name()->as_C_string(), path_index, THREAD);
    }

We need to do that before returning the transformed class. Will fix.

Thanks!

Jiangli



> 
> 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
>>>> 
>>> 
>> 
>