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

[David Holmes]

On 7/12/2020 5:44 pm, Chris Plummer wrote:
> 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.

Not really. I consider pinAll should pin-all as the name implies. The 
question of when to pin should be handled by the caller of pinAll. If 
there were ever to be a second reason to pinAll then you would have to 
decide what semantics that has: does it maintain a count, or is it like 
thread suspension.

David

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