RFR 8237351: Add method to SystemABI for explicitly freeing upcall stubs

[Maurizio Cimadamore]

Very well done sir.

You need to sprinkle some javadoc in the newly added method - with some 
@throws tag too. Other than that looks good.

Maurizio


On 17/01/2020 12:19, Jorn Vernee wrote:
> Hi,
>
> Please review the following:
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8237351
> Webrev: 
> http://cr.openjdk.java.net/~jvernee/panama/webrevs/8237351/webrev.00/
>
> This adds a freeUpcallStub method to SystemABI for explicitly freeing 
> an upcall stub, and uses it in some of the existing tests with a mix 
> of Cleaner and explicit calls.
>
> I slightly changed the native implementation to bail out when it sees 
> that we are trying to pass an address that is not a stub (previously 
> this was just an assert), and now returns a boolean that indicates 
> whether freeing succeeded, so that we can throw an exception when it 
> doesn't (for instance in the case that a random address is passed).
>
> Thanks,
> Jorn
>