Re: Finalization and CNI

[Bryce McKinlay <bryce at mckinlay dot net dot nz>]

On Wednesday, June 11, 2003, at 08:59 AM, Craig A. Vanderborgh wrote:

> include <gcj/cni.h>
> #include <stdio.h>
> #include "HelloWorld.h"
>
> void HelloWorld::print() {
>   printf("Hello, world from CNI!\n");
>
>   void *alloc = new char[1024];
> }
>
> Presumably "alloc" is going to be leaked, correct?

Correct. If your using "new" in CNI code, Java objects are allocated by 
the garbage collector just like they would be in Java, but non-Java 
objects are allocated on the non-garbage collected heap in the same was 
as they would be in C++.

> Is the correct thing
> to do to put the deallocation stuff into the destructor for the
> HelloWorld class?  Would my destructor then get called at some point?

That should work. Just be careful not to leave pointers to Java objects 
in the C++ heap, as while objects allocated there are not eligible for 
collection, they will be scanned for pointers by the collector.

As an alternative, consider using GCJ's _Jv_AllocBytes: see 
http://gcc.gnu.org/onlinedocs/gcc-3.3/gcj/Object-allocation.html

For example:

char *alloc = (char *)_Jv_AllocBytes(1024 * sizeof(char))

will give you a garbage-collected "alloc" whose contents is not scanned 
by the collector. You should only store "native" data in an object 
allocated by this function - not reference to Java objects - or the 
collector could end up freeing Java objects that are still reachable 
from your CNI code.

Bryce.