RFR: 8078644: CDS needs to support JVMTI CFLH

[Jiangli Zhou]

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
>