RFR: 8339725: Concurrent GC crashed due to GetMethodDeclaringClass [v5]

[Liang Mao]

On Wed, 11 Sep 2024 02:23:10 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Liang Mao has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Exclude libagent8339725.cpp compiling for windows
>
> src/hotspot/share/prims/jvmtiEnv.cpp line 3216:
> 
>> 3214:   NULL_CHECK(method, JVMTI_ERROR_INVALID_METHODID);
>> 3215:   Klass* k = method->method_holder();
>> 3216:   Handle holder(Thread::current(), k->klass_holder()); // keep the klass alive
> 
> How do we know `k` is not already unloaded?

As @fisk mentioned above, `k->is_loader_alive()` is checked in caller `jvmti_GetMethodDeclaringClass`. So we won't enter here if k is already unloaded.  The exception this PR handles is to deal with the `k` in the middle of concurrent marking that `is_loader_alive` returns `true` but could be unloaded soon. We'd better keep it alive just like accessing weak reference.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/20907#discussion_r1753067662