RFR: 8258836: JNI local refs exceed capacity getDiagnosticCommandInfo [v2]

[Chris Plummer]

On Tue, 19 Jan 2021 10:14:14 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> This patch adds some explicit capacity for local refs. New regression test
>> fails prior and passes after the patch.
>> 
>> Thoughts?
>
> Severin Gehwolf has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge test files into one
>  - Adress review feedback from dholmes
>  - Merge branch 'master' into JDK-8258836-check-jni-mbeanserver
>  - 8258836: JNI local refs exceed capacity getDiagnosticCommandInfo

src/jdk.management/share/native/libmanagement_ext/DiagnosticCommandImpl.c line 113:

> 111:       return NULL;
> 112:     }
> 113:     (*env)->PopLocalFrame(env, obj);

This needs to assign the result to `obj` in order to get the affect you are looking for. Otherwise it is really no different than passing in `NULL.`, and in the `SetObjectArrayElement` that follows you'll end up assigning a popped localref. I'm surprised this didn't result in some sort of test failure. Are you testing with `num_args > 1`? Perhaps the localref frames are not eagerly reused.

src/jdk.management/share/native/libmanagement_ext/DiagnosticCommandImpl.c line 172:

> 170:   }
> 171:   if (num_commands == 0) {
> 172:       (*env)->PopLocalFrame(env, result);

Also here you need to assign the result to `result`.

src/jdk.management/share/native/libmanagement_ext/DiagnosticCommandImpl.c line 222:

> 220:           return NULL;
> 221:       }
> 222:       (*env)->PopLocalFrame(env, obj);

...and assign to `obj` here.

src/jdk.management/share/native/libmanagement_ext/DiagnosticCommandImpl.c line 227:

> 225:       EXCEPTION_CHECK_AND_FREE(dcmd_info_array);
> 226:   }
> 227:   (*env)->PopLocalFrame(env, result);

...and assign to `result` here.

-------------

PR: https://git.openjdk.java.net/jdk/pull/2130