RFR(L): 8186842: Use Java class loaders for creating the CDS archive

[Ioi Lam]

On 8/29/17 12:55 PM, Jiangli Zhou wrote:
> I was looking for code that handles anonymous classes. There are following code in classLoader.cpp and metaspaceShared.cpp. However, I can’t find any code that specifically removes anonymous classes from the system dictionary at CDS dump time. I’m probably missing something, how do we guarantee (besides the assert) anonymous classes are not being archived?
>
> 1582 void ClassLoader::record_shared_class_loader_type(InstanceKlass* ik, const ClassFileStream* stream) {
> 1583   assert(DumpSharedSpaces, "sanity");
> 1584   assert(stream != NULL, "sanity");
> 1585
> 1586   if (ik->is_anonymous()) {
> 1587     // We do not archive anonymous classes.
> 1588     return;
> 1589   }
> 487 NOT_PRODUCT(
>   488 static void assert_not_anonymous_class(InstanceKlass* k) {
>   489   if (k->is_instance_klass()) {
>   490     assert(!(k->is_anonymous()), "cannot archive anonymous classes");
>   491   }
>   492 }
>   494 static void assert_no_anonymoys_classes_in_dictionaries() {
>   495   ClassLoaderDataGraph::dictionary_classes_do(assert_not_anonymous_class);
>   496 })
Hi Jiangli,

Anonymous classes are not stored inside any Dictionaries. They are 
created by SystemDictionary::parse_stream() with a non-null host_klass:

// Note: this method is much like resolve_from_stream, but
// does not publish the classes via the SystemDictionary.
// Handles unsafe_DefineAnonymousClass and redefineclasses
// RedefinedClasses do not add to the class hierarchy
InstanceKlass* SystemDictionary::parse_stream(Symbol* class_name,
                                               Handle class_loader,
                                               Handle protection_domain,
ClassFileStream* st,
                                               const InstanceKlass* 
host_klass,
GrowableArray<Handle>* cp_patches,
                                               TRAPS)

Anonymous classes are referenced in other data structures, such as in 
this loader_data:

     loader_data = 
ClassLoaderData::anonymous_class_loader_data(class_loader(), CHECK_NULL);

However, all these places are ignored by CDS during dump time (We only 
archive classes that are directly stored in the Dictionary objects of 
the boot/platform/app loaders. See 
SystemDictionary::combine_shared_dictionaries() in the new code).

Therefore, we can guarantee that no anonymous classes are archived. The 
assert_no_anonymous_classes_in_dictionaries() just ensure this is true 
(i.e., in future VM development, if people start putting anonymous 
classes in the Dictionary objects of the boot/platform/app loaders, this 
assert would catch it).

Thanks
- Ioi