Begin working on a garbage collector.

src/refcount.c

@@ -7,10 +7,12 @@ libab_result libab_ref_new(libab_ref* ref, void* data,
     libab_result result = LIBAB_SUCCESS;
     ref->null = 0;
     ref->strong = 1;
-    ref->data = data;
     if ((ref->count = malloc(sizeof(*(ref->count))))) {
+        ref->count->data = data;
         ref->count->strong = ref->count->weak = 1;
         ref->count->free_func = free_func;
+        ref->count->prev = NULL;
+        ref->count->next = NULL;
     } else {
         result = LIBAB_MALLOC;
     }
@@ -19,11 +21,81 @@ libab_result libab_ref_new(libab_ref* ref, void* data,
 
 void libab_ref_null(libab_ref* ref) { ref->null = 1; }
 
+void _ref_gc_count_visit(libab_ref_count* ref, libab_visitor_function_ptr func, void* data) {
+    if(ref->strong && ref->visit_children) ref->visit_children(ref->data, func, data);
+}
+void libab_ref_gc_visit(libab_ref* ref, libab_visitor_function_ptr func, void* data) {
+    _ref_gc_count_visit(ref->count, func, data);
+}
+
+void _libab_ref_gc_list_append(libab_ref_gc_list* list,
+                               libab_ref_count* node) {
+    if(node->next) node->next->prev = node->prev;
+    if(node->prev) node->prev->next = node->next;
+
+    node->prev = list->tail;
+    node->next = NULL;
+    if(list->head) {
+        list->tail->next = node;
+    } else {
+        list->head = node;
+    }
+    list->tail = node;
+}
+void libab_ref_gc_add(libab_ref* ref,
+                      libab_visit_function_ptr visit_children,
+                      libab_ref_gc_list* list) {
+    ref->count->visit_children = visit_children;
+    _libab_ref_gc_list_append(list, ref->count);
+}
+
+void _ref_gc_decrement(libab_ref_count* count, void* data) {
+    count->gc--;
+}
+void _ref_gc_save(libab_ref_count* count, void* data) {
+    libab_ref_gc_list* list = data;
+    if(count->gc != -1) {
+        count->gc = -1;
+        _libab_ref_gc_list_append(list, count);
+        _ref_gc_count_visit(count, _ref_gc_save, data);
+    }
+}
+
+void libab_ref_gc_run(libab_ref_gc_list* list) {
+    libab_ref_gc_list safe;
+    libab_ref_count* head;
+    size_t count = 0;
+
+    head = list->head;
+    while(head) {
+        head->gc = head->weak;
+    }
+
+    head = list->head;
+    while(head) {
+        _ref_gc_count_visit(head, _ref_gc_decrement, NULL);
+    }
+
+    head = list->head;
+    while(head) {
+        _ref_gc_count_visit(head, _ref_gc_save, &safe);
+    }
+
+    head = list->head;
+    while(head) {
+        count++;
+    }
+    printf("Can free %d\n", count);
+
+    list->head = safe.head;
+    list->tail = safe.tail;
+}
+
 void _libab_ref_changed(libab_ref* ref) {
     if (ref->count->strong == 0) {
         ref->count->strong--;
         if (ref->count->free_func) {
-            ref->count->free_func(ref->data);
+            ref->count->free_func(ref->count->data);
         }
     }
     if (ref->count->weak == 0) {
@@ -67,7 +139,7 @@ void libab_ref_data_free(void* data) { free(data); }
 void* libab_ref_get(const libab_ref* ref) {
     void* to_return = NULL;
     if (!ref->null && ref->count->strong > 0) {
-        to_return = ref->data;
+        to_return = ref->count->data;
     }
     return to_return;
 }