On Feb 16, 2016 2:38 PM, "Oliver Schulz" <[email protected]>
wrote:
>
> Hello,
>
> I realized that this question is probably not specific to Cxx.jl, but
concerns Julia's garbage collection in general: Is it save to keep a
pointer to a Julia-owned object in an FFI environment (e.g. from C), as
long as the object is not GC'ed? From what I saw, the current Julia garbage
collector is non-moving. Should I be prepared for Julia to switch to a
moving/compacting GC in the foreseeable future, or is a next-generation GC
for Julia likely to be non-moving as well?
We'd like to try out moving but even if it is implemented, we will
definitely have a relatively easy way to pin the object.
>
>
> Cheers,
>
> Oliver
>
>
> On Thursday, February 11, 2016 at 1:09:44 PM UTC+1, Oliver Schulz wrote:
>>
>> Hi,
>>
>> is the memory address (seen from C++) of objects created via `@cxx
SomeClass()` (or similar) stable over time (GC cycles)?
>>
>> I need to use a container class whose elements keep a pointer to the
container itself. I want Julia to own the container, so it should be
subject to garbage collection. The container owns it's elements and deletes
them on destruction, so they can't outlive the container object. But
obviously, the address of the container object must not change over time,
else things will break. So is it safe to do
>>
>> container = @cxx Container()
>>
>> or
>>
>> container = icxx""" Container(); """
>>
>> Or do I need to do something like
>>
>> container = icxx""" std::unique_ptr<Container>(new Container); """
>>
>> I would assume that "container.data" moves around during GC cycles, so
that `icxx""" &$container """` wouldn't be stable over GC cycles. But this
little test seems to indicate that it actually may be stable:
>>
>> cxx"""
>> struct MyContainer {
>> MyContainer* m_origAddr;
>> MyContainer* origAddr() { return m_origAddr; }
>> MyContainer* currAddr() { return this; }
>> bool checkAddr() { return currAddr() == origAddr(); }
>> MyContainer() { m_origAddr = this; }
>> };
>> """
>>
>> typealias MyContainer
cxxt"MyContainer"{Int(icxx"""sizeof(MyContainer);""")}
>>
>> rndarray = rand(1000,1000,100)
>>
>> containers = Vector{MyContainer}()
>> for i in 1:20000000 push!(containers, @cxx MyContainer()) end
>> assert(all(x -> icxx""" $x.checkAddr(); """, containers))
>>
>> rndarray = rand(10,10,10)
>> gc()
>>
>> assert(all(x -> icxx""" $x.checkAddr(); """, containers))
>>
>> Keno, help ... ? ;-)
>>
>>
>> Cheers,
>>
>> Oliver
>>
