1 files changed, 74 insertions, 0 deletions
diff --git a/components/script_bindings/finalize.rs b/components/script_bindings/finalize.rs
new file mode 100644
index 00000000000..fa1079b5624
--- /dev/null
+++ b/components/script_bindings/finalize.rs
@@ -0,0 +1,74 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Generic finalizer implementations for DOM binding implementations.
+
+use std::any::type_name;
+use std::{mem, ptr};
+
+use js::glue::JS_GetReservedSlot;
+use js::jsapi::JSObject;
+use js::jsval::UndefinedValue;
+use js::rust::GCMethods;
+
+use crate::codegen::PrototypeList::PROTO_OR_IFACE_LENGTH;
+use crate::utils::{ProtoOrIfaceArray, get_proto_or_iface_array};
+use crate::weakref::{DOM_WEAK_SLOT, WeakBox, WeakReferenceable};
+
+/// Drop the resources held by reserved slots of a global object
+unsafe fn do_finalize_global(obj: *mut JSObject) {
+    let protolist = get_proto_or_iface_array(obj);
+    let list = (*protolist).as_mut_ptr();
+    for idx in 0..PROTO_OR_IFACE_LENGTH as isize {
+        let entry = list.offset(idx);
+        let value = *entry;
+        <*mut JSObject>::post_barrier(entry, value, ptr::null_mut());
+    }
+    let _: Box<ProtoOrIfaceArray> = Box::from_raw(protolist);
+}
+
+/// # Safety
+/// `this` must point to a valid, non-null instance of T.
+pub unsafe fn finalize_common<T>(this: *const T) {
+    if !this.is_null() {
+        // The pointer can be null if the object is the unforgeable holder of that interface.
+        let _ = Box::from_raw(this as *mut T);
+    }
+    debug!("{} finalize: {:p}", type_name::<T>(), this);
+}
+
+/// # Safety
+/// `obj` must point to a valid, non-null JS object.
+/// `this` must point to a valid, non-null instance of T.
+pub unsafe fn finalize_global<T>(obj: *mut JSObject, this: *const T) {
+    do_finalize_global(obj);
+    finalize_common::<T>(this);
+}
+
+/// # Safety
+/// `obj` must point to a valid, non-null JS object.
+/// `this` must point to a valid, non-null instance of T.
+pub unsafe fn finalize_weak_referenceable<T: WeakReferenceable>(
+    obj: *mut JSObject,
+    this: *const T,
+) {
+    let mut slot = UndefinedValue();
+    JS_GetReservedSlot(obj, DOM_WEAK_SLOT, &mut slot);
+    let weak_box_ptr = slot.to_private() as *mut WeakBox<T>;
+    if !weak_box_ptr.is_null() {
+        let count = {
+            let weak_box = &*weak_box_ptr;
+            assert!(weak_box.value.get().is_some());
+            assert!(weak_box.count.get() > 0);
+            weak_box.value.set(None);
+            let count = weak_box.count.get() - 1;
+            weak_box.count.set(count);
+            count
+        };
+        if count == 0 {
+            mem::drop(Box::from_raw(weak_box_ptr));
+        }
+    }
+    finalize_common::<T>(this);
+}