RFR: 8268406: Deallocate jmethodID native memory

Coleen Phillimore coleenp at openjdk.org
Thu Jun 12 12:45:16 UTC 2025


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 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.

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Commit messages:
 - 8305626: Kitchensink7D.java failing because of native memory exhausting with ZGC

Changes: https://git.openjdk.org/jdk/pull/25267/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25267&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8268406
  Stats: 596 lines in 14 files changed: 315 ins; 223 del; 58 mod
  Patch: https://git.openjdk.org/jdk/pull/25267.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25267/head:pull/25267

PR: https://git.openjdk.org/jdk/pull/25267


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