extern void *afb_context_data(struct afb_context *context, void *(*make_value)(void), void (*free_value)(void*));
extern void afb_context_close(struct afb_context *context);
extern void *afb_context_data(struct afb_context *context, void *(*make_value)(void), void (*free_value)(void*));
extern void afb_context_close(struct afb_context *context);