replace refcount with gc root for c extensions

Fixes #44

gc.c

@@ -29,7 +29,6 @@ inline void cb_gc_register(struct cb_gc_header *obj, size_t size,
 {
 	obj->deinit = deinit_fn;
 	obj->mark = 0;
-	obj->refcount = 0;
 	obj->size = size;
 	obj->next = allocated;
 	allocated = obj;
@@ -42,18 +41,6 @@ inline int cb_gc_should_collect(void)
 		|| amount_allocated > next_allocation_threshold;
 }
 
-inline void cb_gc_adjust_refcount(cb_gc_header *obj, int amount)
-{
-	obj->refcount += amount;
-	if (obj->refcount == 0) {
-		hint += 1;
-		if (cb_gc_should_collect()) {
-			DEBUG_LOG("collecting due to refcount hint");
-			cb_gc_collect();
-		}
-	}
-}
-
 inline void cb_gc_mark(struct cb_gc_header *obj)
 {
 	obj->mark = 1;
@@ -95,6 +82,34 @@ static void evaluate_mark_queue(void)
 	}
 }
 
+struct cext_root {
+	struct cext_root *prev, *next;
+	struct cb_value value;
+};
+
+static struct cext_root *cext_root = NULL;
+
+struct cext_root *cb_gc_hold(struct cb_value value)
+{
+	struct cext_root *node = malloc(sizeof(struct cext_root));
+	node->prev = NULL;
+	node->next = cext_root;
+	node->value = value;
+	cext_root = node;
+	return node;
+}
+
+void cb_gc_release(struct cext_root *node)
+{
+	if (node->prev)
+		node->prev->next = node->next;
+	if (node->next)
+		node->next->prev = node->prev;
+	if (node == cext_root)
+		cext_root = node->next;
+	free(node);
+}
+
 static void mark(void)
 {
 	struct cb_module *mod;
@@ -133,6 +148,10 @@ static void mark(void)
 			cb_value_mark(&f->func);
 	}
 
+	DEBUG_LOG("marking c ext roots");
+	for (struct cext_root *node = cext_root; node; node = node->next)
+		cb_value_mark(&node->value);
+
 	evaluate_mark_queue();
 }
 
@@ -145,16 +164,15 @@ static void sweep(void)
 	while (current) {
 		tmp = current;
 		current = current->next;
-		if (!tmp->mark && tmp->refcount == 0) {
+		if (!tmp->mark) {
 			*prev_ptr = tmp->next;
 			if (tmp->deinit)
 				tmp->deinit(tmp);
 			DEBUG_LOG("freeing object at %p", tmp);
 			amount_allocated -= tmp->size;
 			free(tmp);
 		} else {
-			DEBUG_LOG("not freeing object at %p (%s)", tmp,
-					tmp->mark ? "mark" : "refcount");
+			DEBUG_LOG("not freeing object at %p", tmp);
 			tmp->mark = 0;
 			prev_ptr = &tmp->next;
 		}
@@ -172,4 +190,4 @@ void cb_gc_collect(void)
 	DEBUG_LOG("end; allocated=%zu, collected=%zu, next collection at %zu",
 			amount_allocated, before - amount_allocated,
 			next_allocation_threshold);
-}
+}

gc.h

@@ -7,12 +7,13 @@ typedef void (cb_deinit_fn)(void *);
 
 typedef struct cb_gc_header {
 	struct cb_gc_header *next;
-	int refcount;
 	int mark;
 	size_t size;
 	cb_deinit_fn *deinit;
 } cb_gc_header;
 
+typedef struct cext_root cb_value_hold;
+
 void cb_gc_mark(cb_gc_header *obj);
 int cb_gc_is_marked(cb_gc_header *obj);
 void cb_gc_adjust_refcount(cb_gc_header *obj, int amount);
@@ -25,4 +26,7 @@ void cb_gc_register(cb_gc_header *obj, size_t size, cb_deinit_fn *deinit_fn);
 struct cb_value;
 void cb_gc_queue_mark(struct cb_value *obj);
 
-#endif
+cb_value_hold *cb_gc_hold(struct cb_value value);
+void cb_gc_release(cb_value_hold *hold);
+
+#endif

modules/fs.c

@@ -133,7 +133,10 @@ struct cb_struct_spec *get_stat_struct_spec(void)
 	F("mtime");
 	F("ctime");
 
-	cb_gc_adjust_refcount(&spec->gc_header, 1); /* Never collect it */
+	struct cb_value spec_value;
+	spec_value.type = CB_VALUE_STRUCT_SPEC;
+	spec_value.val.as_struct_spec = spec;
+	cb_gc_hold(spec_value); /* Never collect it */
 	return spec;
 #undef F
 }
@@ -487,4 +490,4 @@ void cb_fs_instantiate(struct cb_module *mod)
 #define SET_CONST(C) CB_SET_EXPORT(mod, ident_ ## C, cb_int(C));
 	CONSTS(SET_CONST);
 #undef SET_CONST
-}
+}

value.c

@@ -16,54 +16,6 @@
 #include "struct.h"
 #include "value.h"
 
-static void adjust_refcount(struct cb_value *value, int amount)
-{
-	cb_gc_header *header;
-
-	switch (value->type) {
-	case CB_VALUE_ARRAY:
-		header = &value->val.as_array->gc_header;
-		break;
-	case CB_VALUE_STRING:
-		header = &value->val.as_string->gc_header;
-		break;
-	case CB_VALUE_BYTES:
-		header = &value->val.as_bytes->gc_header;
-		break;
-	case CB_VALUE_FUNCTION:
-		header = &value->val.as_function->gc_header;
-		break;
-	case CB_VALUE_STRUCT:
-		header = &value->val.as_struct->gc_header;
-		break;
-	case CB_VALUE_USERDATA:
-		header = &value->val.as_userdata->gc_header;
-		break;
-
-	default:
-		return;
-	}
-
-	if (cb_options.debug_gc) {
-		cb_str as_str = cb_value_to_string(value);
-		printf("GC: adjusted refcount by %d for object at %p: %s\n",
-				amount, header, cb_strptr(&as_str));
-		cb_str_free(as_str);
-	}
-
-	cb_gc_adjust_refcount(header, amount);
-}
-
-inline void cb_value_incref(struct cb_value *value)
-{
-	adjust_refcount(value, 1);
-}
-
-inline void cb_value_decref(struct cb_value *value)
-{
-	adjust_refcount(value, -1);
-}
-
 static void cb_function_deinit(void *ptr)
 {
 	struct cb_user_function ufn;
@@ -868,4 +820,4 @@ struct cb_value cb_bytes_new_value(size_t size)
 	val.val.as_bytes = cb_bytes_new(size);
 
 	return val;
-}
+}