Finalization and dead references: another proposal

[Peter Levart]

Hi Remi,

On 12/07/2017 07:12 PM, Remi Forax wrote:
>>> So no magic here. Just API.
>> This is an API version of Hans’s #3 approach.  As he said, there’s
>> performance overhead and nothing guarantees that the referent is kept alive
>> - that’s an implementation artifact.
> it's not even true, the implementation do not even guarantee that the referent field will be kept on stack,
> a value type can disappear completely if its field are not used,
> so without a reachabilityFence somewhere, it will not work.
>

What do you mean by saying "the implementation do not even guarantee 
that the referent field will be kept on stack".

If a referent is passed through a reference typed parameter to the JNI 
method (there's no other way actually), then such referent must be kept 
alive for the entire time the native method executes, because native 
method may call methods or access fields on such referent. Because 
there's no cross-native-baundary optimization going on currently, JNI 
must guarantee that. If/when there will be cross-native-baundary 
optimization, I suppose native side would have to have an equivalent to 
reachabilityFence too ...

Regards, Peter