c('PL_agc_hook')

Documentation
- Reference manual
  - Foreign Language Interface
    - The Foreign Include File
      - Foreign Code Hooks
        
        PL_dispatch_hook()
        
        PL_abort_hook()
        
        PL_abort_unhook()
        
        PL_on_halt()
        
        PL_exit_hook()
        
        PL_agc_hook()
- Packages

Availability:C-language interface function

PL_agc_hook_t PL_agc_hook(PL_agc_hook_t new)

Register a hook with the atom-garbage collector (see garbage_collect_atoms/0) that is called on any atom that is reclaimed. The old hook is returned. If no hook is currently defined, NULL is returned. The argument of the called hook is the atom that is to be garbage collected. The return value is an int. If the return value is zero, the atom is not reclaimed. The hook may invoke any Prolog predicate.

The example below defines a foreign library for printing the garbage collected atoms for debugging purposes.

#include <SWI-Stream.h>
#include <SWI-Prolog.h>

static int
atom_hook(atom_t a)
{ Sdprintf("AGC: deleting %s\n", PL_atom_chars(a));

  return TRUE;
}

static PL_agc_hook_t old;

install_t
install()
{ old = PL_agc_hook(atom_hook);
}

install_t
uninstall()
{ PL_agc_hook(old);
}