On Thu, 17 Jul 2025 22:38:48 GMT, Ioi Lam <ik...@openjdk.org> wrote:
> This PR loads the classes for the boot/platform/app loaders with
> `AOTLinkedClassBulkLoader::preload_classes()`. This happens at the very
> beginning of `vmClasses::resolve_all()`, before any Java code is executed.
>
> - We essentially iterate over all the classes inside the
> `AOTLinkedClassTable` and adds them into the system dictionary using the new
> method `SystemDictionary::preload_class()`.
> - `SystemDictionary::preload_class(..., k)` is lightweight because it's
> called in a single thread after all super types of `k` have been loaded. So
> most of the complicated work (such as place holders, circularity detection,
> etc) in `SystemDictionary::resolve_or_null(..., k)` can be skipped. We also
> don't need to call into `ClassLoader::load_class()` as the boot/platform/app
> loaders are well-behaved.
> - In the assembly phase, we record the mirror, package, protection domain,
> code source, etc, of these classes. So there's no need to programmatically
> create them in the production run. See `HeapShared::copy_java_mirror()` and
> also changes in ClassLoader.java and SecureClassLoader.java.
src/hotspot/share/cds/aotLinkedClassBulkLoader.cpp line 96:
> 94: // later in load_javabase_classes() and load_non_javabase_classes().
> 95:
> preload_classes_in_table(AOTLinkedClassTable::for_static_archive()->boot1(),
> "boot1", Handle(), CHECK);
> 96:
> preload_classes_in_table(AOTLinkedClassTable::for_static_archive()->boot2(),
> "boot2", Handle(), CHECK);
why do we maintain both a `boot1` and `boot2` set here when both are loaded
before executing any Java code? Is the distinction meaningful for preloaded
classes given both are loaded into the same classloader?
src/hotspot/share/cds/aotLinkedClassBulkLoader.cpp line 127:
> 125: precond(ik->local_interfaces()->at(i)->is_loaded());
> 126: }
> 127: });
This debugging check is duplicated in `SystemDictionary::preload_class` in the
`#ifdef ASSERT` block.
src/hotspot/share/cds/cdsHeapVerifier.cpp line 241:
> 239: }
> 240: if (field_ik == vmClasses::Boolean_klass()) {
> 241: // TODO: check if is TRUE or FALSE
Are we canonicalizing Boolean.TRUE & Boolean.FALSE and thus don't care if a
static field points to them? And Boolean.TYPE isn't getting the same treatment?
src/hotspot/share/classfile/javaClasses.cpp line 1017:
> 1015: void java_lang_Class::set_mirror_module_field(JavaThread* current,
> Klass* k, Handle mirror, Handle module) {
> 1016: if (CDSConfig::is_using_preloaded_classes()) {
> 1017: oop archived_module = java_lang_Class:: module(mirror());
Suggestion:
oop archived_module = java_lang_Class::module(mirror());
src/java.base/share/classes/java/net/URL.java line 1768:
> 1766:
> 1767: @AOTRuntimeSetup
> 1768: private static void runtimeSetup() {
Slightly concerned with this for reasons I'm still trying to track down -
Mostly around the `URLStreamHandler` that each URL instance holds onto.
Can we create cases were the cached URLStreamHandler for a URL from the
assembly phase would be different than the URLStreamHandler looked up in the
production run?
src/java.base/share/classes/jdk/internal/loader/NativeLibraries.java line 407:
> 405: static class Holder {
> 406: // All native libraries we've loaded.
> 407: private static final Set<String> loadedLibraryNames =
I'm concerned about this causing problems if we ever AOT initialize a user
class that calls `System.loadLibrary` from its static initializer.
Should we add a check to the `clear()` method above to ensure that only the
expected libraries have been loaded during the assembly phase?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/26375#discussion_r2283111220
PR Review Comment: https://git.openjdk.org/jdk/pull/26375#discussion_r2283328974
PR Review Comment: https://git.openjdk.org/jdk/pull/26375#discussion_r2283162998
PR Review Comment: https://git.openjdk.org/jdk/pull/26375#discussion_r2283173361
PR Review Comment: https://git.openjdk.org/jdk/pull/26375#discussion_r2283406179
PR Review Comment: https://git.openjdk.org/jdk/pull/26375#discussion_r2291474398
