And just to complete my explanation, you are in fact using the
scm_dynwind_* functions slightly differently from their intended use. In
the example of gnc_scm_to_locale_string the net result is the same, but
in locations where it matters you won't get the desired memory leak
protection effect.
A minimal code snippet:
str = scm_to_locale_string(scm_string);
scm_dynwind_begin (0);
call_other_scm_function; /* potentially non-local exiting function */
scm_dynwind_free (str); /* wrong: too late */
scm_dynwind_end ();
What happens here is that call_other_scm_function may exit non-locally
(for example because it triggers the error catch code internally). If
that happens, scm_dynwind_free is never reached and str won't be freed.
scm_dynwind_free is not actually freeing memory itself, but it tells
guile to free the memory whenever the dynwind context is left (locally
by reaching scm_dynwind_end or non-locally). So this function should be
called *before* calling any function that might exit non-locally. The
proper invocation would be:
str = scm_to_locale_string(scm_string);
scm_dynwind_begin (0);
scm_dynwind_free (str); /* ok */
call_other_scm_function; /* potentially non-local exiting function */
scm_dynwind_end ();
In this case, str is first marked for freeing (but not freed yet !)
whenever the context ends and only then the potentially non-local
exiting function is called. In this case str is guaranteed to be freed:
if other_scm_function succeeds, str will be freed once scm_dynwind_end
is reached. If it fails the non-local exit is detected internally and
str is freed then.
As said before, for gnc_scm_to_locale_string this didn't matter really,
because g_strdup is never exiting non-locally from guile's point of view.
I hope this helps clearing it up.
Geert
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