On Tue, 17 Jun 2025 13:59:54 GMT, Coleen Phillimore <cole...@openjdk.org> wrote:
>> This change uses a ConcurrentHashTable to associate Method* with jmethodID, >> instead of an indirection. JNI is deprecated in favor of using Panama to >> call methods, so I don't think we're concerned about JNI performance going >> forward. JVMTI uses a lot of jmethodIDs but there aren't any performance >> tests for JVMTI, but running vmTestbase/nsk/jvmti with in product build with >> and without this change had no difference in time. >> >> The purpose of this change is to remove the memory leak when you unload >> classes: we were leaving the jmethodID memory just in case JVMTI code still >> had references to that jmethodID and instead of crashing, should get >> nullptr. With this change, if JVMTI looks up a jmethodID, we've removed it >> from the table and will return nullptr. Redefinition and the >> InstanceKlass::_jmethod_method_ids is somewhat complicated. When a method >> becomes "obsolete" in redefinition, which means that the code in the method >> is changed, afterward creating a jmethodID from an "obsolete" method will >> create a new entry in the InstanceKlass table. This mechanism increases the >> method_idnum to do this. In the future maybe we could throw >> NoSuchMethodError if you try to create a jmethodID out of an obsolete method >> and remove all this code. But that's not in this change. >> >> Tested with tier1-4, 5-7. > > Coleen Phillimore has updated the pull request incrementally with one > additional commit since the last revision: > > Use load_acquire only in the places that need it. This is really great optimization and refactoring! Looks pretty good to me but I'd like to make one more pass through the changes. src/hotspot/share/oops/instanceKlass.cpp line 2412: > 2410: } > 2411: > 2412: // Lookup or create a jmethodID Nit: Add dot at the end. src/hotspot/share/oops/instanceKlass.cpp line 2472: > 2470: // Allocate a larger one and copy entries to the new one. > 2471: // They've already been updated to point to new methods where > applicable (i.e., not obsolete). > 2472: jmethodID* new_cache = create_jmethod_id_cache(size); Nice micro-refactoring! src/hotspot/share/oops/jmethodIDTable.hpp line 48: > 46: static void remove(jmethodID mid); > 47: > 48: // RedefineClasses support Nit: Add a dot at the end of the comment for consistency with other comments. src/hotspot/share/oops/method.hpp line 718: > 716: > 717: static void change_method_associated_with_jmethod_id(jmethodID > old_jmid_ptr, Method* new_method); > 718: static bool validate_method_id(jmethodID mid); Nit: I'd suggest to name it `validate_jmethod_id` for consistency. ------------- PR Review: https://git.openjdk.org/jdk/pull/25267#pullrequestreview-2937302206 PR Review Comment: https://git.openjdk.org/jdk/pull/25267#discussion_r2153333668 PR Review Comment: https://git.openjdk.org/jdk/pull/25267#discussion_r2153332839 PR Review Comment: https://git.openjdk.org/jdk/pull/25267#discussion_r2153323790 PR Review Comment: https://git.openjdk.org/jdk/pull/25267#discussion_r2153315538
