RFR: 8078644: CDS needs to support JVMTI CFLH

[Jiangli Zhou]

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
>> 
>