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 when the AOT cache was created, and when the AOT cache is used. **Testing** - New test cases are added to test specific behaviors of the `-XX:+AOTClassLinking` flag - A new test group `hotspot_aot_classlinking` is created for running existing CDS tests with the `-XX:+AOTClassLinking` flag. Note that this group filters out test cases that are incompatible with `-XX:+AOTClassLinking`. E.g., classes that use JVMTI ClassFileLoadHook or class redefinition. - We will also modify some of our internal test cases (e.g., with large applications) to also run with the `-XX:+AOTClassLinking` flag. --- See [here](https://bugs.openjdk.org/browse/JDK-8315737) for the sequence of dependent RFEs for implementing JEP 483. ------------- Depends on: https://git.openjdk.org/jdk/pull/20517 Commit messages: - More clean up - Merge branch 'jep-483-step-02-8338018-rename-class-prelinker-to-aot-cp-resolver' into jep-483-step-03-8329706-implement-xx-aot-class-linking - Merge branch 'jep-483-step-02-8338018-rename-class-prelinker-to-aot-cp-resolver' into jep-483-step-03-8329706-implement-xx-aot-class-linking - 8329706: Implement -XX:+AOTClassLinking Changes: https://git.openjdk.org/jdk/pull/20843/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20843&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8329706 Stats: 1734 lines in 46 files changed: 1577 ins; 52 del; 105 mod Patch: https://git.openjdk.org/jdk/pull/20843.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/20843/head:pull/20843 PR: https://git.openjdk.org/jdk/pull/20843
