vm: introduce value registry

Introduce a new, lazily allocated value registry which can be used by C
code to store values which should not be garbage collected.

The registry is a plain ucode object internally and treated as GC root
but not exposed to ucode script code, this allows it to retain references
to values which are otherwise completely unreachable from ucode scripts.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

include/ucode/types.h

@@ -250,6 +250,7 @@ struct uc_vm {
 	uc_upvalref_t *open_upvals;
 	uc_parse_config_t *config;
 	uc_value_t *globals;
+	uc_value_t *registry;
 	uc_source_t *sources;
 	uc_weakref_t values;
 	uc_resource_types_t restypes;

include/ucode/vm.h

@@ -119,6 +119,11 @@ void uc_vm_free(uc_vm_t *vm);
 uc_value_t *uc_vm_scope_get(uc_vm_t *vm);
 void uc_vm_scope_set(uc_vm_t *vm, uc_value_t *ctx);
 
+bool uc_vm_registry_exists(uc_vm_t *vm, const char *key);
+uc_value_t *uc_vm_registry_get(uc_vm_t *vm, const char *key);
+void uc_vm_registry_set(uc_vm_t *vm, const char *key, uc_value_t *value);
+bool uc_vm_registry_delete(uc_vm_t *vm, const char *key);
+
 void uc_vm_stack_push(uc_vm_t *vm, uc_value_t *value);
 uc_value_t *uc_vm_stack_pop(uc_vm_t *vm);
 uc_value_t *uc_vm_stack_peek(uc_vm_t *vm, size_t offset);

types.c

@@ -2078,6 +2078,7 @@ ucv_gc_common(uc_vm_t *vm, bool final)
 	if (!final) {
 		/* mark reachable objects */
 		ucv_gc_mark(vm->globals);
+		ucv_gc_mark(vm->registry);
 		ucv_gc_mark(vm->exception.stacktrace);
 
 		for (i = 0; i < vm->callframes.count; i++) {

vm.c

@@ -2480,3 +2480,34 @@ uc_vm_trace_set(uc_vm_t *vm, uint32_t level)
 {
 	vm->trace = level;
 }
+
+bool
+uc_vm_registry_exists(uc_vm_t *vm, const char *key)
+{
+	bool exists;
+
+	ucv_object_get(vm->registry, key, &exists);
+
+	return exists;
+}
+
+uc_value_t *
+uc_vm_registry_get(uc_vm_t *vm, const char *key)
+{
+	return ucv_object_get(vm->registry, key, NULL);
+}
+
+void
+uc_vm_registry_set(uc_vm_t *vm, const char *key, uc_value_t *value)
+{
+	if (!vm->registry)
+		vm->registry = ucv_object_new(vm);
+
+	ucv_object_add(vm->registry, key, value);
+}
+
+bool
+uc_vm_registry_delete(uc_vm_t *vm, const char *key)
+{
+	return ucv_object_delete(vm->registry, key);
+}