[plt-scheme] Memory management and MzScheme

On Sat, 23 Nov 2002, Pedro Pinto wrote:
> I am trying to build an extension for MzScheme on WindowsXp/Visual Studio
> 7.0. I seem to be unable to figure out what is wrong with:
> 
> static Scheme_Object *scheme_test(int argc, Scheme_Object **argv)
> {
>     std::vector<Scheme_Object *> v;
>     for(int i =0 ; i < 10000; i++)
>         v.push_back(scheme_make_string ("test"));
>     return scheme_build_list (10000,&v[0]);
> }

Are you loading into DrScheme or MrEd, and not just MzScheme?
Could it be that C++ is new'ing space for v?  If so, that might
be your problem, because MrEd replaces the new operator so that
its C++ objects are garbage collected.  Eventually, your C++ objects
will get garbage-collected too!  That was our experience in linux.
We linked our C++ extension with a copy of new/delete that uses
malloc/free, so it wouldn't get linked at loadtime with MrEd's new/delete.

Ron Stanonik
stanonik at cogsci.ucsd.edu

/*
  MrEd replaces the new operator so that C++ objects are garbage collected.
  Eventually, your C++ objects will get garbage-collected too!

  Compile
    gcc -g -I/plt200src/include -c gcdemo.c
    gcc -g -shared -o gcdemo.so gcdemo.o /plt200src/lib/mzdyn.o

  Start mred
    (load-extension "gcdemo.so")
    (arf)  - returns 3
    do some scheme
    (collect-garbage)
    (arf)  - returns 0

  Or start drscheme
    (load-extension "gcdemo.so")
    (arf)  - returns 3
    (arf)  - returns 3
    (arf)  - returns 3
    hit the GC button
    (arf)  - returns something other 3
 */

#include "escheme.h"

class arf {
  public:
    int x;
    arf();
};

arf::arf()
{
  x = 3;
}

arf *arfp;

static Scheme_Object *sch_arf(int argc, Scheme_Object **argv)
{
  if (!arfp) arfp = new arf;
  return scheme_make_integer(arfp->x);
}

Scheme_Object *scheme_module_name()
{
  /* This extension doesn't define a module: */
  return scheme_false;
}

Scheme_Object *scheme_reload(Scheme_Env *env)
{
  Scheme_Object *proc;

  proc = scheme_make_prim_w_arity(sch_arf, "arf", 0, 0);
  scheme_add_global("arf", proc, env);

  return scheme_make_string("Hello Pad!");
}

Scheme_Object *scheme_initialize(Scheme_Env *env)
{
  return scheme_reload(env);
}