FAQ FOOD! Re: scm_must_malloc and memory leaking?

[Marius Vollmer <mvo@zagadka.ping.de>]

forcer <forcer@mindless.com> writes:

> Hmm...
> When using
> 
> 	f = scm_must_malloc(sizeof(some_struct));
> 	f->data = scm_must_malloc(size);
> 
> and there won't be enough free memory for the second
> scm_must_malloc even after gc, the allocated memory in f is
> lost and won't be free'd. Is that true? and if yes, how can i
> prevent it?

Yes, I think there is a leak.  Maybe you can use `malloc objects'.  I
once made a wrapper for them, this might show you how to use them.
This is old code, so before it goes into the FAQ, it should be
checked.

    #include <guile/gh.h>
    #include <libguile.h>

    /* Allocate some memory and stuff a magic Scheme value into *HANDLE so
       that the memory gets freed when *HANDLE gets collected.  Typically,
       HANDLE points to some variable on the C stack.  When this variable
       goes out of scope, the memory gets freed.  It might help the
       garbage collector when you overwrite this variable after the memory
       is no longer needed. */

    void *gh_malloc_collected SCM_P ((size_t n, SCM *handle));

    void *
    gh_malloc_collected (n, handle)
	 size_t n;
	 SCM *handle;
    {
      *handle = scm_malloc_obj (n);
      if (*handle == SCM_BOOL_F)
	scm_memory_error ("gh_malloc_collected");
      return SCM_MALLOCDATA(*handle);
    }

    void gh_detach_memory SCM_P ((SCM handle));

    void
    gh_detach_memory (handle)
	 SCM handle;
    {
      SCM_SETMALLOCDATA(handle, NULL);
    }