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/* 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 http://mozilla.org/MPL/2.0/. */
use glue;
use jsapi::root::*;
use rust::GCMethods;
use std::cell::UnsafeCell;
use std::ptr;
/// Types that can be traced.
///
/// This trait is unsafe; if it is implemented incorrectly, the GC may end up
/// collecting objects that are still reachable.
pub unsafe trait Trace {
unsafe fn trace(&self, trc: *mut JSTracer);
}
/**
* The Heap<T> class is a heap-stored reference to a JS GC thing. All members of
* heap classes that refer to GC things should use Heap<T> (or possibly
* TenuredHeap<T>, described below).
*
* Heap<T> is an abstraction that hides some of the complexity required to
* maintain GC invariants for the contained reference. It uses operator
* overloading to provide a normal pointer interface, but notifies the GC every
* time the value it contains is updated. This is necessary for generational GC,
* which keeps track of all pointers into the nursery.
*
* Heap<T> instances must be traced when their containing object is traced to
* keep the pointed-to GC thing alive.
*
* Heap<T> objects should only be used on the heap. GC references stored on the
* C/C++ stack must use Rooted/Handle/MutableHandle instead.
*
* Type T must be a public GC pointer type.
*
* Note that the rust version of Heap<T> implements different barriers to the
* C++ version, which also provides features to help integration with
* cycle-collected C++ objects. That version has a read barrier which performs
* gray unmarking and also marks the contents during an incremental GC. This
* version has a pre-write barrier instead, and this enforces the
* snapshot-at-the-beginning invariant which is necessary for incremental GC in
* the absence of the read barrier.
*/
#[repr(C)]
#[derive(Debug)]
pub struct Heap<T: GCMethods + Copy> {
ptr: UnsafeCell<T>,
}
impl<T: GCMethods + Copy> Heap<T> {
pub fn new(v: T) -> Heap<T>
where
Heap<T>: Default,
{
let ptr = Heap::default();
ptr.set(v);
ptr
}
pub fn set(&self, v: T) {
unsafe {
let ptr = self.ptr.get();
let prev = *ptr;
*ptr = v;
T::write_barriers(ptr, prev, v);
}
}
pub fn get(&self) -> T {
unsafe { *self.ptr.get() }
}
pub unsafe fn get_unsafe(&self) -> *mut T {
self.ptr.get()
}
pub fn handle(&self) -> JS::Handle<T> {
unsafe { JS::Handle::from_marked_location(self.ptr.get() as *const _) }
}
pub fn handle_mut(&self) -> JS::MutableHandle<T> {
unsafe { JS::MutableHandle::from_marked_location(self.ptr.get()) }
}
}
impl<T: GCMethods + Copy> Clone for Heap<T>
where
Heap<T>: Default,
{
fn clone(&self) -> Self {
Heap::new(self.get())
}
}
impl<T: GCMethods + Copy + PartialEq> PartialEq for Heap<T> {
fn eq(&self, other: &Self) -> bool {
self.get() == other.get()
}
}
impl<T> Default for Heap<*mut T>
where
*mut T: GCMethods + Copy,
{
fn default() -> Heap<*mut T> {
Heap {
ptr: UnsafeCell::new(ptr::null_mut()),
}
}
}
impl Default for Heap<JS::Value> {
fn default() -> Heap<JS::Value> {
Heap {
ptr: UnsafeCell::new(JS::Value::default()),
}
}
}
impl<T: GCMethods + Copy> Drop for Heap<T> {
fn drop(&mut self) {
unsafe {
let prev = self.ptr.get();
T::write_barriers(prev, *prev, T::initial());
}
}
}
// Creates a C string literal `$str`.
macro_rules! c_str {
($str:expr) => {
concat!($str, "\0").as_ptr() as *const ::std::os::raw::c_char
};
}
unsafe impl Trace for Heap<*mut JSFunction> {
unsafe fn trace(&self, trc: *mut JSTracer) {
glue::CallFunctionTracer(trc, self as *const _ as *mut Self, c_str!("function"));
}
}
unsafe impl Trace for Heap<*mut JSObject> {
unsafe fn trace(&self, trc: *mut JSTracer) {
glue::CallObjectTracer(trc, self as *const _ as *mut Self, c_str!("object"));
}
}
unsafe impl Trace for Heap<*mut JSScript> {
unsafe fn trace(&self, trc: *mut JSTracer) {
glue::CallScriptTracer(trc, self as *const _ as *mut Self, c_str!("script"));
}
}
unsafe impl Trace for Heap<*mut JSString> {
unsafe fn trace(&self, trc: *mut JSTracer) {
glue::CallStringTracer(trc, self as *const _ as *mut Self, c_str!("string"));
}
}
#[cfg(feature = "bigint")]
unsafe impl Trace for Heap<*mut JS::BigInt> {
unsafe fn trace(&self, trc: *mut JSTracer) {
glue::CallBigIntTracer(trc, self as *const _ as *mut Self, c_str!("bigint"));
}
}
unsafe impl Trace for Heap<JS::Value> {
unsafe fn trace(&self, trc: *mut JSTracer) {
glue::CallValueTracer(trc, self as *const _ as *mut Self, c_str!("value"));
}
}
unsafe impl Trace for Heap<jsid> {
unsafe fn trace(&self, trc: *mut JSTracer) {
glue::CallIdTracer(trc, self as *const _ as *mut Self, c_str!("id"));
}
}
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