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

[Chris Plummer]

On Mon, 7 Dec 2020 06:27:20 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> src/jdk.jdwp.agent/share/native/libjdwp/threadControl.c line 1560:
>> 
>>> 1558:              * garbage collected while the VM is suspended.
>>> 1559:              */
>>> 1560:             commonRef_pinAll();
>> 
>> Can we have multiple VM.suspend calls? The  suspendAllCount seems to suggest that. In which case shouldn't we only pin on the 0->1 transition, and only unpin on the 1->0 transition?
>
> That was something I pointed out in the pre-review, and it has been addressed in `commonRef_pinAll/unpinAll`:
> 
> `568         if (gdata->pinAllCount == 1) {`
> `618         if (gdata->pinAllCount == 0) {`

> Okay. I would not have handled it at that level, but would have had
pinAll/unpinAll operate unconditionally, but the calls to those methods
being conditional based on the suspendAllCount.
>
>David

Well, that's assuming `pinAll()` will only ever be used by by `suspendAll()`. One could imaging a future use, such as if `VirtualMachine.disableCollection()` were ever to be added.

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