servo/components/script/dom/bindings/finalize.rs

/* 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;

use js::glue::JS_GetReservedSlot;
use js::jsapi::JSObject;
use js::jsval::UndefinedValue;

use crate::dom::bindings::utils::finalize_global as do_finalize_global;
use crate::dom::bindings::weakref::{WeakBox, WeakReferenceable, DOM_WEAK_SLOT};

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);
}

pub unsafe fn finalize_global<T>(obj: *mut JSObject, this: *const T) {
    do_finalize_global(obj);
    finalize_common::<T>(this);
}

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);
}