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Manish Goregaokar 2014-09-24 05:31:56 +05:30
parent cc44a3b064
commit 5336dd9853
2 changed files with 11 additions and 15 deletions
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15
components/script/dom/bindings/DESIGN.md
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@ -13,13 +13,14 @@ This is very tricky and magically mechanism helped by Rust Compiler.
The outline is: The outline is:
1. SpiderMonkey's GC calls `JSClass.trace` defined in `FooBinding` when marking phase. This JSClass is basis of each wrapper JSObject. 1. SpiderMonkey's GC calls `JSClass.trace` defined in `FooBinding` when marking phase. This JSClass is basis of each wrapper JSObject.
2. `JSClass.trace` calls `Foo::trace()` defined in InhertTypes.rs. 2. `JSClass.trace` calls `Foo::trace()` (an implementation of `JSTraceable`).
3. `Foo::trace()` calls `Foo::encode()`. This `encode()` method is derived by the annotation of `#[deriving(Encodable)]` for a Rust DOM Element struct. This is typically derived via a #[jstraceable] annotation
4. `Foo::encode()` calls `JS<T>::encode()` method of `JS<T>` which is contained to `Foo`’s member. So this is the compiler magic! Rust compiler generates [codes like this](https://github.com/mozilla/rust/blob/db5206c32a879d5058d6a5cdce39c13c763fbdd5/src/libsyntax/ext/deriving/encodable.rs) for all structs annotated `#[deriving(Encodable)]`. This is based on [the assumption](https://github.com/mozilla/servo/blob/54da52fa774ce2ee59fcf811af595bf292169ad8/src/components/script/dom/bindings/trace.rs#L16). 3. For all fields (except those wrapped in `Untraceable`), `Foo::trace()`
5. `JS<T>::encode()` calls `dom::bindings::trace::trace_reflector()`. calls `trace()` on the field. For example, for fields of type `JS<T>`, `JS<T>::trace()` calls
6. `trace_reflector()` fetches the reflector that is reachable from a Rust object, and notifies it to the GC with using JSTracer. `trace_reflector()`.
7. This operation continues to the end of the graph. 4. `trace_reflector()` fetches the reflector that is reachable from a Rust object, and notifies it to the GC with using JSTracer.
8. Finally, GC gets whether Rust object lives or not from JSObjects which is hold by Rust object. 5. This operation continues to the end of the graph.
6. Finally, GC gets whether Rust object lives or not from JSObjects which is hold by Rust object.
## Destruct ## Destruct

11
components/script/dom/bindings/trace.rs
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@ -13,13 +13,13 @@
//! through `ProxyTraps.trace` otherwise.) //! through `ProxyTraps.trace` otherwise.)
//! 2. `_trace` calls `Foo::trace()` (an implementation of `JSTraceable`). //! 2. `_trace` calls `Foo::trace()` (an implementation of `JSTraceable`).
//! This is typically derived via a #[jstraceable] annotation //! This is typically derived via a #[jstraceable] annotation
//! 4. For all fields (except those wrapped in `Untraceable`), `Foo::trace()` //! 3. For all fields (except those wrapped in `Untraceable`), `Foo::trace()`
//! calls `trace()` on the field. //! calls `trace()` on the field.
//! For example, for fields of type `JS<T>`, `JS<T>::trace()` calls //! For example, for fields of type `JS<T>`, `JS<T>::trace()` calls
//! `trace_reflector()`. //! `trace_reflector()`.
//! 6. `trace_reflector()` calls `trace_object()` with the `JSObject` for the //! 4. `trace_reflector()` calls `trace_object()` with the `JSObject` for the
//! reflector. //! reflector.
//! 7. `trace_object()` calls `JS_CallTracer()` to notify the GC, which will //! 5. `trace_object()` calls `JS_CallTracer()` to notify the GC, which will
//! add the object to the graph, and will trace that object as well. //! add the object to the graph, and will trace that object as well.
//! //!
//! The untraceable!() macro adds an empty implementation of JSTraceable to //! The untraceable!() macro adds an empty implementation of JSTraceable to
@ -44,11 +44,6 @@ use std::collections::hashmap::HashMap;
use collections::hash::Hash; use collections::hash::Hash;
use style::PropertyDeclarationBlock; use style::PropertyDeclarationBlock;
// IMPORTANT: We rely on the fact that we never attempt to encode DOM objects using
// any encoder but JSTracer. Since we derive trace hooks automatically,
// we are unfortunately required to use generic types everywhere and
// unsafely cast to the concrete JSTracer we actually require.
impl<T: Reflectable> JSTraceable for JS<T> { impl<T: Reflectable> JSTraceable for JS<T> {
fn trace(&self, trc: *mut JSTracer) { fn trace(&self, trc: *mut JSTracer) {
trace_reflector(trc, "", self.reflector()); trace_reflector(trc, "", self.reflector());