RFR: 8219687: G1 asserts nmethod should not be unloaded during parallel code cache unloading

[Erik Osterlund]

Hi Thomas,

Thanks for the review. Will fix that comment.

/Erik

> On 7 Jun 2019, at 11:52, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi Erik,
> 
>> On Mon, 2019-06-03 at 17:39 +0200, Erik Österlund wrote:
>> Hi,
>> 
>> There is an assert that G1 occasionally hits during parallel code
>> cache unloading.
>> When oops_do() is called to compute is_unloading(), the nmethod
>> should not be unloaded says the assert.
>> 
>> However... imagine the following scenario:
>> 
>> [...]
>> 
>> So there is absolutely no harm with calling oops_do on nmethods that 
>> racingly become unloaded here, and that assertion should just be
>> silenced.
>> 
>> Webrev:
>> http://cr.openjdk.java.net/~eosterlund/8219687/webrev.00/
>> 
>> Bug:
>> https://bugs.openjdk.java.net/browse/JDK-8219687
> 
>  looks good.
> 
> Could you fix the comment in the call to nmethod::oops_do() in
> shenandoahCodeRoots.cpp too?
> 
> No need for re-review.
> 
> Thanks,
>  Thomas
> 
>