RFR: 8255987: JDI tests fail with com.sun.jdi.ObjectCollectedException

[David Holmes]

On Fri, 4 Dec 2020 21:22:53 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> src/jdk.jdwp.agent/share/native/libjdwp/commonRef.c line 632:
>> 
>>> 630:                     if (weakRef == NULL) {
>>> 631:                         EXIT_ERROR(AGENT_ERROR_NULL_POINTER,"NewWeakGlobalRef");
>>> 632:                     }
>> 
>> I'm not so sure I agree that having a fatal error here is the right thing to do. The only other user of `weakenNode()` is `ObjectReference.disableCollection()`. It returns an error to the debugger if `weakenNode()` returns `NULL`. However, I'm not so sure that's a good thing to do here either, since it means the `VM.resume()` will need to fail. Possibly the error should just be ignored, and we live with the ref staying strong.
>
> Another options is to save away the weakref in the node when strengthening. This would benefit `ObjectReference.disableCollection()` also, since it would no longer need to deal with a potential OOM. However, I'm not so sure it's actually worth doing. Trying to keep the debug session alive will having allocation errors is probably a fools errand.

I agree a fatal error here seems excessive. Simply maintaining the strong ref seems reasonable.

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PR: https://git.openjdk.java.net/jdk/pull/1595