valgrind and CNI

[Andrew Haley]

David Blasby writes:
 > I wrote a few example programs and the garbage collector seemed to be
 > doing exactly what it was supposed to do.
 > 
 > See the "memory management" section at the bottom of this wiki:
 > 
 > http://docs.codehaus.org/display/GEOS/Compiling+JTS

This is because:

 > > it conservatively scans the stack.

Andrew.

 > 
 > Thanks,
 > dave
 > 
 > >  > I was originally using valgrind to make sure that GCJ wasnt garbage
 > >  > collecting my Java objects when I passed them from C++ to C.  For
 > >  > example, I use Geometry.h (created using gcjh) in the C++ library, but
 > >  > a "typedef struct Geometry Geometry;" in the "C" program.
 > >  >
 > >  > Java creates an Object, hands it off to the C++ library as a Geometry*
 > >  > class, then gets passed as a pointer to the "C" program.  I thought
 > >  > the garbage collector might collect the java object between the time
 > >  > it leaves the C++ library and arrives at the "C" program.
 > > 
 > > It might.  gcj allocates its own objects, and only scans items
 > > reachable from its roots.  In addition, it conservatively scans the
 > > stack.  If you want to ensure that a gcj object is not reclaimed, you
 > > should make very sure that it is reachable from a Java object
 > > somewhere: this is as easy as declaring a static reference in some
 > > Java class and pointing it at the object you want not to be reclaimed.
 > > 
 > > Andrew.
 > >