On Thu, 12 Sep 2024 21:43:24 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:
>
> @ashu-mehra comments
src/hotspot/share/cds/aotClassLinker.cpp line 227:
> 225: }
> 226:
> 227: int AOTClassLinker::num_initiated_classes(oop loader1, oop loader2) {
The two loader arguments here are quite confusing marking it hard to understand
the code. Can it be refactored as this:
int AOTClassLinker::num_platform_initiated_classes() {
// AOTLinkedClassBulkLoader will initiate loading of all public boot classes
in the platform loader.
return num_initiated_classes(nullptr);
}
int AOTClassLinker::num_app_initiated_classes() {
// AOTLinkedClassBulkLoader will initiate loading of all public boot/platform
classes in the app loader.
return num_platform_initiated_classes +
num_initiated_classes(SystemDictionary::java_platform_loader());
}
int AOTClassLinker::num_initiated_classes(oop loader) {
int n = 0;
for (int i = 0; i < _sorted_candidates->length(); i++) {
InstanceKlass* ik = _sorted_candidates->at(i);
if (ik->is_public() && !ik->is_hidden() &&
(ik->class_loader() == loader) {
n++;
}
}
return n;
}
src/hotspot/share/cds/aotLinkedClassBulkLoader.cpp line 199:
> 197: InstanceKlass* ik = classes->at(i);
> 198: assert(ik->is_loaded(), "must have already been loaded by a parent
> loader");
> 199: assert(ik->class_loader() != initiating_loader(), "must be a parent
> loader");
Can we also add an assert that ik->class_loader() must be either boot or
platform loader.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1759128918
PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1759129552
