mirror of
https://github.com/servo/servo.git
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239 lines
No EOL
6.9 KiB
Rust
239 lines
No EOL
6.9 KiB
Rust
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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//! Utilities for tracing JS-managed values.
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//!
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//! The lifetime of DOM objects is managed by the SpiderMonkey Garbage
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//! Collector. A rooted DOM object implementing the interface `Foo` is traced
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//! as follows:
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//!
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//! 1. The GC calls `_trace` defined in `FooBinding` during the marking
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//! phase. (This happens through `JSClass.trace` for non-proxy bindings, and
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//! through `ProxyTraps.trace` otherwise.)
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//! 2. `_trace` calls `Foo::trace()` (an implementation of `JSTraceable`).
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//! This is typically derived via a #[jstraceable] annotation
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//! 3. For all fields (except those wrapped in `Untraceable`), `Foo::trace()`
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//! calls `trace()` on the field.
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//! For example, for fields of type `JS<T>`, `JS<T>::trace()` calls
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//! `trace_reflector()`.
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//! 4. `trace_reflector()` calls `trace_object()` with the `JSObject` for the
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//! reflector.
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//! 5. `trace_object()` calls `JS_CallTracer()` to notify the GC, which will
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//! add the object to the graph, and will trace that object as well.
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//!
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//! The untraceable!() macro adds an empty implementation of JSTraceable to
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//! a datatype.
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use dom::bindings::js::JS;
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use dom::bindings::utils::{Reflectable, Reflector};
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use js::jsapi::{JSObject, JSTracer, JS_CallTracer, JSTRACE_OBJECT};
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use js::jsval::JSVal;
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use libc;
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use std::rc::Rc;
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use std::cell::{Cell, RefCell};
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use url::Url;
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use servo_util::atom::Atom;
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use servo_util::namespace::Namespace;
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use msg::constellation_msg::{PipelineId, SubpageId, WindowSizeData};
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use net::image_cache_task::ImageCacheTask;
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use script_traits::ScriptControlChan;
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use std::collections::hashmap::HashMap;
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use collections::hash::Hash;
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use style::PropertyDeclarationBlock;
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impl<T: Reflectable> JSTraceable for JS<T> {
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fn trace(&self, trc: *mut JSTracer) {
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trace_reflector(trc, "", self.reflector());
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}
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}
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untraceable!(Reflector)
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/// A trait to allow tracing (only) DOM objects.
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pub trait JSTraceable {
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fn trace(&self, trc: *mut JSTracer);
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}
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/// Trace a `JSVal`.
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pub fn trace_jsval(tracer: *mut JSTracer, description: &str, val: JSVal) {
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if !val.is_markable() {
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return;
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}
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unsafe {
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let name = description.to_c_str();
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(*tracer).debugPrinter = None;
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(*tracer).debugPrintIndex = -1;
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(*tracer).debugPrintArg = name.as_ptr() as *const libc::c_void;
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debug!("tracing value {:s}", description);
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JS_CallTracer(tracer, val.to_gcthing(), val.trace_kind());
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}
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}
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/// Trace the `JSObject` held by `reflector`.
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#[allow(unrooted_must_root)]
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pub fn trace_reflector(tracer: *mut JSTracer, description: &str, reflector: &Reflector) {
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trace_object(tracer, description, reflector.get_jsobject())
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}
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/// Trace a `JSObject`.
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pub fn trace_object(tracer: *mut JSTracer, description: &str, obj: *mut JSObject) {
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unsafe {
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let name = description.to_c_str();
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(*tracer).debugPrinter = None;
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(*tracer).debugPrintIndex = -1;
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(*tracer).debugPrintArg = name.as_ptr() as *const libc::c_void;
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debug!("tracing {:s}", description);
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JS_CallTracer(tracer, obj as *mut libc::c_void, JSTRACE_OBJECT);
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}
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}
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/// Encapsulates a type that cannot easily have `Encodable` derived automagically,
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/// but also does not need to be made known to the SpiderMonkey garbage collector.
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///
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/// Use only with types that are not associated with a JS reflector and do not contain
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/// fields of types associated with JS reflectors.
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///
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/// This should really only be used for types that are from other crates,
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/// so we can't implement `Encodable`. See more details: mozilla#2662.
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pub struct Untraceable<T> {
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inner: T,
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}
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impl<T> Untraceable<T> {
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pub fn new(val: T) -> Untraceable<T> {
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Untraceable {
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inner: val
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}
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}
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}
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impl<T> Deref<T> for Untraceable<T> {
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fn deref<'a>(&'a self) -> &'a T {
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&self.inner
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}
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}
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impl<T> DerefMut<T> for Untraceable<T> {
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fn deref_mut<'a>(&'a mut self) -> &'a mut T {
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&mut self.inner
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}
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}
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/// Encapsulates a type that can be traced but is boxed in a type we don't
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/// control (such as `RefCell`).
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///
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/// Wrap a field in Traceable and implement the `Encodable` trait
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/// for that new concrete type to achieve magic compiler-derived trace hooks.
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///
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/// We always prefer this, in case the contained type ever changes to something that should be traced.
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/// See more details: mozilla#2662.
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#[deriving(PartialEq, Clone)]
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pub struct Traceable<T> {
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inner: T
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}
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impl<T> Traceable<T> {
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pub fn new(val: T) -> Traceable<T> {
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Traceable {
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inner: val
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}
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}
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}
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impl<T> Deref<T> for Traceable<T> {
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fn deref<'a>(&'a self) -> &'a T {
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&self.inner
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}
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}
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impl<T: JSTraceable> JSTraceable for RefCell<T> {
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fn trace(&self, trc: *mut JSTracer) {
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self.borrow().trace(trc)
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}
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}
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impl<T: JSTraceable> JSTraceable for Rc<T> {
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fn trace(&self, trc: *mut JSTracer) {
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self.deref().trace(trc)
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}
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}
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impl<T: JSTraceable> JSTraceable for Box<T> {
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fn trace(&self, trc: *mut JSTracer) {
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(**self).trace(trc)
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}
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}
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impl<T: JSTraceable+Copy> JSTraceable for Traceable<Cell<T>> {
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fn trace(&self, trc: *mut JSTracer) {
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self.deref().get().trace(trc)
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}
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}
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impl<T: JSTraceable+Copy> JSTraceable for Cell<T> {
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fn trace(&self, trc: *mut JSTracer) {
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self.get().trace(trc)
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}
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}
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impl JSTraceable for Traceable<*mut JSObject> {
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fn trace(&self, trc: *mut JSTracer) {
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trace_object(trc, "object", **self);
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}
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}
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impl JSTraceable for Traceable<JSVal> {
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fn trace(&self, trc: *mut JSTracer) {
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trace_jsval(trc, "val", **self);
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}
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}
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// XXXManishearth Check if the following three are optimized to no-ops
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// if e.trace() is a no-op (e.g it is an untraceable type)
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impl<T: JSTraceable> JSTraceable for Vec<T> {
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#[inline]
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fn trace(&self, trc: *mut JSTracer) {
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for e in self.iter() {
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e.trace(trc);
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}
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}
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}
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impl<T: JSTraceable> JSTraceable for Option<T> {
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#[inline]
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fn trace(&self, trc: *mut JSTracer) {
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self.as_ref().map(|e| e.trace(trc));
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}
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}
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impl<K: Eq+Hash, V: JSTraceable> JSTraceable for HashMap<K, V> {
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#[inline]
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fn trace(&self, trc: *mut JSTracer) {
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for e in self.iter() {
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e.val1().trace(trc);
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}
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}
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}
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untraceable!(bool, f32, f64, String, Url)
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untraceable!(uint, u8, u16, u32, u64)
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untraceable!(int, i8, i16, i32, i64)
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untraceable!(Untraceable<T>)
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untraceable!(ImageCacheTask, ScriptControlChan)
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untraceable!(Atom, Namespace)
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untraceable!(PropertyDeclarationBlock)
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// These three are interdependent, if you plan to put jsmanaged data
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// in one of these make sure it is propagated properly to containing structs
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untraceable!(SubpageId, WindowSizeData, PipelineId)
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impl<'a> JSTraceable for &'a str {
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#[inline]
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fn trace(&self, _: *mut JSTracer) {
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// Do nothing
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}
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} |