Re: Storing C++ data in an instance field using CNI?

[Bryce McKinlay <mckinlay at redhat dot com>]

Stanley Brown wrote:

> > > is it possible using CNI to store C++ data in the object as an
> instance field?
>
> As earlier mentioned the best way to do this is to store the struct 
> address in a long java variable.  Why long?  Well, to be honest 64-bit 
> systems will eventually become the norm which means you will probably 
> have to convert your program later.  Think ahead now and write it for 
> 64 bit systems in mind since that will still work with 32 bit systems 
> (just get alot of warnings during compilation about casting int to long).


If this is for CNI, the recommended type to use is RawData. This will be 
pointer-length no matter what system you compile it on.

> Also remember to override the finalize method of your Java object that 
> is storing the native struct to call a native method to free/delete 
> the native struct.  Very important!!  If you dont do this C/C++ will 
> not deallocate the memory reserved for your native struct when the 
> Java class is GCed.


I'm thinking of adding something like "RawDataMarked" which would be 
like RawData but would be checked by the GC. This way you could allocate 
a native struct using JvAllocBytes(), and it would be automatically 
freed when the Java object becomes unreachable. No need for a finalizer.

Thoughts? Anyone got an idea for a better name for it?

Regards

Bryce