On Tue, 3 Sep 2024 20:57:48 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 > exact same set of modules are visible whe...
src/hotspot/share/cds/aotClassLinker.hpp line 101: > 99: // When CDS is enabled, is ik guatanteed to be linked at deployment > time (and > 100: // cannot be replaced by JVMTI, etc)? > 101: // This is a necessary (not but sufficient) condition for keeping a > direct pointer Suggestion: // This is a necessary (but not sufficient) condition for keeping a direct pointer src/hotspot/share/cds/aotClassLinker.hpp line 106: > 104: static bool is_candidate(InstanceKlass* ik); > 105: > 106: // Request that ik to be added to the candidates table. This will > return succeed only if Suggestion: // Request that ik be added to the candidates table. This will return true only if ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1746508873 PR Review Comment: https://git.openjdk.org/jdk/pull/20843#discussion_r1746510269
