MemorySegment.close() is not idempotent

[forax at univ-mlv.fr]

----- Mail original -----
> De: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>, "panama-dev at openjdk.java.net'" <panama-dev at openjdk.java.net>
> Envoyé: Lundi 15 Mars 2021 11:53:31
> Objet: Re: MemorySegment.close() is not idempotent

> Hi Remi,
> this kind of issues is gonna be superseded by the upcoming work in:
> 
> https://github.com/openjdk/panama-foreign/pull/466
> 
> As part of that work, MemorySegment will lose the AutoCloseable
> interface, and lifecycle will be managed in a different entity, called
> ResourceScope (which is attached onto a segment).
> 
> Now, closing ResourceScope is still not idem-potent, but I believe that,
> with the new API, closing a scope twice is something you might want to
> get notified about, as it 99% signals a bug in your code.
> 
> I think it would be great if you could adjust the experiment to the new
> API and see how much of a problem that is in there?

I will, but not before next week end :(

> 
> P.S.
> in the new API, if two resources (e.g. unsigned and signed) have same
> lifecycle, they should be backed by same ResourceScope abstraction.

Ok, i will take a look.

> 
> Maurizio

Rémi

> 
> On 15/03/2021 09:11, Remi Forax wrote:
>> To play with panama.foreign, i've partially re-implement the Apache Arrow [1]
>> columnar format in pure Java.
>> So i've a bunch of dataset class that are wrappers of one or two MemorySegment
>> (two if the data can be nullable) that represent a column of data.
>>
>> I stumble on is the fact that a MemorySegment can not be closed more than once.
>>  From dataset, i can be wrapped to another one, think by example the unsigned int
>>  dataset being a wrapper on top on the signed one, but they share the same
>>  MemorySegment.
>>
>> As a user i want to write something like
>>    try(var dataset = IntDataSet.from(MemorySegment.allocateMemory(5 * 4));
>>        var unsignedDataset = dataset.asUnsigned()) {
>>      ...
>>    }
>>
>> the problem is that the MemorySegment.close() is not idempotent, so i've to
>> check myself (with isAlive()) if the MemorySegment of a dataset has already
>> been closed or not.
>>
>> Did i miss something ?
>>
>> regards,
>> Rémi
>>
> > [1] https://arrow.apache.org/docs/index.html