On Tue, 10 Sep 2024 00:53:32 GMT, Ioi Lam <ik...@openjdk.org> wrote:
>> This is the 3rd PR for [JEP 483: Ahead-of-Time Class Loading &
>> Linking](https://bugs.openjdk.org/browse/JDK-8315737).
>>
>> **Overview**
>>
>> - A new `-XX:+AOTClassLinking` flag is added. See [JEP
>> 498](https://bugs.openjdk.org/browse/JDK-8315737) and the
>> [CSR](https://bugs.openjdk.org/browse/JDK-8339506) for a discussion of this
>> command-line option, its default value, and its impact on compatibility.
>> - When this flag is enabled during the creation of an AOT cache (aka CDS
>> archive), an `AOTLinkedClassTable` is added to the cache to include all
>> classes that are AOT-linked. For this PR, only classes for the
>> boot/platform/application loaders are eligible. The main logic is in
>> `aotClassLinker.cpp`.
>> - When an AOT archive is loaded in a production run, all classes in the
>> `AOTLinkedClassTable` are loaded into their respective class loaders at the
>> earliest opportunity. The main logic is in `aotLinkedClassBulkLoader.cpp`.
>> - The boot classes are loaded as part of `vmClasses::resolve_all()`
>> - The platform/application classes are loaded after the module graph is
>> restored (see changes in `threads.cpp`).
>> - Since all classes in a `AOTLinkedClassTable` are loaded before any
>> user-code is executed, we can resolve constant pool entries that refer to
>> these classes during AOT cache creation. See changes in
>> `AOTConstantPoolResolver::is_class_resolution_deterministic()`.
>>
>> **All-or-nothing Loading**
>>
>> - Because AOT-linked classes can refer to each other, using direct C++
>> pointers, all AOT-linked classes must be loaded together. Otherwise we will
>> have dangling C++ pointers in the class metadata structures.
>> - During a production run, we check during VM start-up for incompatible VM
>> options that would prevent some of the AOT-linked classes from being loaded.
>> For example:
>> - If the VM is started with an JVMTI agent that has ClassFileLoadHook
>> capabilities, it could replace some of the AOT-linked classes with
>> alternative versions.
>> - If the VM is started with certain module options, such as
>> `--patch-module` or `--module`, some AOT-linked classes may be replaced with
>> patched versions, or may become invisible and cannot be loaded into the JVM.
>> - When incompatible VM options are detected, the JVM will refuse to load an
>> AOT cache that has AOT-linked classes. See
>> `FileMapInfo::validate_aot_class_linking()`.
>> - For simplfication, `FileMapInfo::validate_aot_class_linking()` requires
>> `CDSConfig::is_using_full_module_graph()` to be true. This means that the
>> exa...
>
> Ioi Lam has updated the pull request incrementally with one additional commit
> since the last revision:
>
> @dholmes-ora comments: logging indents
Looks good as far as I can see -- although I only have a limited familiarity
with the CDS archive code.
src/hotspot/share/cds/aotClassLinker.hpp line 71:
> 69: //
> 70: class AOTClassLinker : AllStatic {
> 71: using ClassesTable = ResourceHashtable<InstanceKlass*, bool, 15889,
> AnyObj::C_HEAP, mtClassShared>;
Can we have a symbolic name for this (prime) magic number here and in other
places in this patch? I realise there is existing code which uses the raw
number bit it is also consumed symbolically (e.g. in archiveBuilder.hpp,
metaspaceClosure.hpp)
src/hotspot/share/cds/aotLinkedClassBulkLoader.cpp line 191:
> 189: }
> 190:
> 191: ClassLoaderData* loader_data =
> ClassLoaderData::class_loader_data(loader());
Can we assert here that loader() != nullptr?
src/hotspot/share/cds/archiveBuilder.cpp line 433:
> 431: }
> 432:
> 433: remember_embedded_pointer_in_enclosing_obj(ref);
I'm not clear why this was moved up. Was this just an omission (bug) in the
earlier version or do we now need to remember a reference location that we
could previously safely ignore?
src/hotspot/share/cds/cdsConfig.cpp line 551:
> 549: }
> 550:
> 551: void CDSConfig::set_has_aot_linked_classes(bool is_static_archive, bool
> has_aot_linked_classes) {
Why does this need to take `is_static_archive` as an argument?
src/hotspot/share/cds/dynamicArchive.cpp line 138:
> 136: verify_estimate_size(_estimated_metaspaceobj_bytes, "MetaspaceObjs");
> 137:
> 138: sort_methods();
Could we have a comment to note that sorting and making shareable need to be
done before calling `AOTClassLinker::write_to_archive();`
-------------
Marked as reviewed by adinn (Reviewer).
PR Review: https://git.openjdk.org/jdk/pull/20843#pullrequestreview-2291991335
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1751666092
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1751745625
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1751916420
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1751952246
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1751964685
