RFR: 8281615: Deadlock caused by jdwp agent [v2]

[Zhengyu Gu]

On Mon, 14 Feb 2022 23:26:17 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   David and Chris' comments
>
> src/jdk.jdwp.agent/share/native/libjdwp/classTrack.c line 215:
> 
>> 213: classTrack_activate(JNIEnv *env)
>> 214: {
>> 215:     struct bag* new_bag = bagCreateBag(sizeof(char*), 1000);
> 
> I don't think there can be any race during activation but this change is harmless.

I am not sure classTrack_activate() has the problem, but it is called outside of initialization, inside debug loop ... so I assume that event callback might happen.

> src/jdk.jdwp.agent/share/native/libjdwp/classTrack.c line 240:
> 
>> 238:     if (deletedSignatures != NULL) {
>> 239:         bagEnumerateOver(deletedSignatures, cleanDeleted, NULL);
>> 240:         to_delete = deletedSignatures;
> 
> `cleanDeleted` also calls `jvmtiDeallocate`, so either both need to be outside the lock or neither.
> 
> It is really unclear to me how many threads can be involved here and which functions can be called when.

Right. Moved `bagEnumerateOver()` outside of lock as well.

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PR: https://git.openjdk.java.net/jdk/pull/7461