RFR: 8178813: Add test for G1 pre-barrier on dereference of weak JNI handles

[Thomas Schatzl]

Hi again,

On Tue, 2017-05-09 at 10:34 +0200, Thomas Schatzl wrote:
> Hi Kim,
> 
> On Tue, 2017-05-09 at 10:08 +0200, Mikael Gerdin wrote:
> > 
> > Hi Kim,
> > [...]
> > On 2017-05-09 07:46, Kim Barrett wrote:
> > > 
> > > [...]
> > > full: http://cr.openjdk.java.net/~kbarrett/8178813/hotspot.01/
> > > incr: http://cr.openjdk.java.net/~kbarrett/8178813/hotspot.01.inc
> > > /
>   some minor comments:
> 
> - I would recommend using whitebox api to issue the correct kind of
> GC instead of calling system.gc() in the first place. This would
> avoid the need to disallow ExplicitGCInvokesConcurrent. It also seems
> to be a minor effort as the test already uses whitebox. If you think
> the loop using system.gc is preferable, feel free to keep it.
> 
> - TestJNIWeakG1.java:206: the printed text does not correspond to the
> method name like the other methods do ("checkShouldNotClear" vs.
> "checkShouldNotCrash")

I do not need a re-review for this change.

> - not sure about the need for the error handling using booleans in
> the main()/check() method. I would think that letting the Exception
> just propagate and the test terminate asap would be sufficient.
> 
> The extra information about the second test failing in case the first
> failed does not seem to be very helpful given that the test is very
> small anyway.

I am okay to keep it as is too, but it only seems some extra
unnecessary code.

Thanks,
  Thomas