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Auto merge of #13106 - servo:trusted, r=nox

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Remove mutex from Trusted

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This commit is contained in:
bors-servo 2016-08-29 05:00:39 -05:00 • committed by GitHub
commit 9e726b4d83
5 changed files with 54 additions and 91 deletions
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129
components/script/dom/bindings/refcounted.rs
View file

@ -6,21 +6,21 @@
//! between threads (or intra-thread for asynchronous events). Akin to Gecko's
//! nsMainThreadPtrHandle, this uses thread-safe reference counting and ensures
//! that the actual SpiderMonkey GC integration occurs on the script thread via
//! message passing. Ownership of a `Trusted<T>` object means the DOM object of
//! weak refcounts. Ownership of a `Trusted<T>` object means the DOM object of
//! type T to which it points remains alive. Any other behaviour is undefined.
//! To guarantee the lifetime of a DOM object when performing asynchronous operations,
//! obtain a `Trusted<T>` from that object and pass it along with each operation.
//! A usable pointer to the original DOM object can be obtained on the script thread
//! from a `Trusted<T>` via the `to_temporary` method.
//!
//! The implementation of Trusted<T> is as follows:
//! A hashtable resides in the script thread, keyed on the pointer to the Rust DOM object.
//! The values in this hashtable are atomic reference counts. When a Trusted<T> object is
//! created or cloned, this count is increased. When a Trusted<T> is dropped, the count
//! decreases. If the count hits zero, a message is dispatched to the script thread to remove
//! the entry from the hashmap if the count is still zero. The JS reflector for the DOM object
//! is rooted when a hashmap entry is first created, and unrooted when the hashmap entry
//! is removed.
//! The implementation of `Trusted<T>` is as follows:
//! The `Trusted<T>` object contains an atomic reference counted pointer to the Rust DOM object.
//! A hashtable resides in the script thread, keyed on the pointer.
//! The values in this hashtable are weak reference counts. When a `Trusted<T>` object is
//! created or cloned, the reference count is increased. When a `Trusted<T>` is dropped, the count
//! decreases. If the count hits zero, the weak reference is emptied, and is removed from
//! its hash table during the next GC. During GC, the entries of the hash table are counted
//! as JS roots.
use core::nonzero::NonZero;
use dom::bindings::js::Root;
@ -28,13 +28,13 @@ use dom::bindings::reflector::{Reflectable, Reflector};
use dom::bindings::trace::trace_reflector;
use js::jsapi::JSTracer;
use libc;
use script_runtime::{CommonScriptMsg, ScriptChan};
use std::cell::RefCell;
use std::collections::hash_map::Entry::{Occupied, Vacant};
use std::collections::hash_map::HashMap;
use std::hash::Hash;
use std::marker::PhantomData;
use std::os;
use std::sync::{Arc, Mutex};
use std::sync::{Arc, Weak};
#[allow(missing_docs)] // FIXME
@ -52,6 +52,12 @@ pub use self::dummy::LIVE_REFERENCES;
pub struct TrustedReference(*const libc::c_void);
unsafe impl Send for TrustedReference {}
impl TrustedReference {
fn new<T: Reflectable>(ptr: *const T) -> TrustedReference {
TrustedReference(ptr as *const libc::c_void)
}
}
/// A safe wrapper around a raw pointer to a DOM object that can be
/// shared among threads for use in asynchronous operations. The underlying
/// DOM object is guaranteed to live at least as long as the last outstanding
@ -60,9 +66,7 @@ unsafe impl Send for TrustedReference {}
pub struct Trusted<T: Reflectable> {
/// A pointer to the Rust DOM object of type T, but void to allow
/// sending `Trusted<T>` between threads, regardless of T's sendability.
ptr: *const libc::c_void,
refcount: Arc<Mutex<usize>>,
script_chan: Box<ScriptChan + Send>,
refcount: Arc<TrustedReference>,
owner_thread: *const libc::c_void,
phantom: PhantomData<T>,
}
@ -74,15 +78,12 @@ impl<T: Reflectable> Trusted<T> {
/// be prevented from being GCed for the duration of the resulting `Trusted<T>` object's
/// lifetime.
pub fn new(ptr: &T) -> Trusted<T> {
let script_chan = ptr.global().r().script_chan();
LIVE_REFERENCES.with(|ref r| {
let r = r.borrow();
let live_references = r.as_ref().unwrap();
let refcount = live_references.addref(&*ptr as *const T);
Trusted {
ptr: &*ptr as *const T as *const libc::c_void,
refcount: refcount,
script_chan: script_chan.clone(),
owner_thread: (&*live_references) as *const _ as *const libc::c_void,
phantom: PhantomData,
}
@ -99,48 +100,26 @@ impl<T: Reflectable> Trusted<T> {
self.owner_thread == (&*live_references) as *const _ as *const libc::c_void
}));
unsafe {
Root::new(NonZero::new(self.ptr as *const T))
Root::new(NonZero::new(self.refcount.0 as *const T))
}
}
}
impl<T: Reflectable> Clone for Trusted<T> {
fn clone(&self) -> Trusted<T> {
{
let mut refcount = self.refcount.lock().unwrap();
*refcount += 1;
}
Trusted {
ptr: self.ptr,
refcount: self.refcount.clone(),
script_chan: self.script_chan.clone(),
owner_thread: self.owner_thread,
phantom: PhantomData,
}
}
}
impl<T: Reflectable> Drop for Trusted<T> {
fn drop(&mut self) {
let mut refcount = self.refcount.lock().unwrap();
assert!(*refcount > 0);
*refcount -= 1;
if *refcount == 0 {
// It's possible this send will fail if the script thread
// has already exited. There's not much we can do at this
// point though.
let msg = CommonScriptMsg::RefcountCleanup(TrustedReference(self.ptr));
let _ = self.script_chan.send(msg);
}
}
}
/// The set of live, pinned DOM objects that are currently prevented
/// from being garbage collected due to outstanding references.
pub struct LiveDOMReferences {
// keyed on pointer to Rust DOM object
table: RefCell<HashMap<*const libc::c_void, Arc<Mutex<usize>>>>,
table: RefCell<HashMap<*const libc::c_void, Weak<TrustedReference>>>,
}
impl LiveDOMReferences {
@ -153,59 +132,55 @@ impl LiveDOMReferences {
});
}
fn addref<T: Reflectable>(&self, ptr: *const T) -> Arc<Mutex<usize>> {
fn addref<T: Reflectable>(&self, ptr: *const T) -> Arc<TrustedReference> {
let mut table = self.table.borrow_mut();
let capacity = table.capacity();
let len = table.len();
if (0 < capacity) && (capacity <= len) {
info!("growing refcounted references by {}", len);
remove_nulls(&mut table);
table.reserve(len);
}
match table.entry(ptr as *const libc::c_void) {
Occupied(mut entry) => {
let refcount = entry.get_mut();
*refcount.lock().unwrap() += 1;
refcount.clone()
}
Occupied(mut entry) => match entry.get().upgrade() {
Some(refcount) => refcount,
None => {
let refcount = Arc::new(TrustedReference::new(ptr));
entry.insert(Arc::downgrade(&refcount));
refcount
},
},
Vacant(entry) => {
let refcount = Arc::new(Mutex::new(1));
entry.insert(refcount.clone());
let refcount = Arc::new(TrustedReference::new(ptr));
entry.insert(Arc::downgrade(&refcount));
refcount
}
}
}
}
/// Unpin the given DOM object if its refcount is 0.
pub fn cleanup(raw_reflectable: TrustedReference) {
let TrustedReference(raw_reflectable) = raw_reflectable;
LIVE_REFERENCES.with(|ref r| {
let r = r.borrow();
let live_references = r.as_ref().unwrap();
let mut table = live_references.table.borrow_mut();
match table.entry(raw_reflectable) {
Occupied(entry) => {
if *entry.get().lock().unwrap() != 0 {
// there could have been a new reference taken since
// this message was dispatched.
return;
}
let _ = entry.remove();
}
Vacant(_) => {
// there could be a cleanup message dispatched, then a new
// pinned reference obtained and released before the message
// is processed, at which point there would be no matching
// hashtable entry.
info!("attempt to cleanup an unrecognized reflector");
}
}
})
/// Remove null entries from the live references table
fn remove_nulls<K: Eq + Hash + Clone, V> (table: &mut HashMap<K, Weak<V>>) {
let to_remove: Vec<K> =
table.iter()
.filter(|&(_, value)| Weak::upgrade(value).is_none())
.map(|(key, _)| key.clone())
.collect();
info!("removing {} refcounted references", to_remove.len());
for key in to_remove {
table.remove(&key);
}
}
/// A JSTraceDataOp for tracing reflectors held in LIVE_REFERENCES
pub unsafe extern "C" fn trace_refcounted_objects(tracer: *mut JSTracer,
_data: *mut os::raw::c_void) {
debug!("tracing live refcounted references");
info!("tracing live refcounted references");
LIVE_REFERENCES.with(|ref r| {
let r = r.borrow();
let live_references = r.as_ref().unwrap();
let table = live_references.table.borrow();
let mut table = live_references.table.borrow_mut();
remove_nulls(&mut table);
for obj in table.keys() {
let reflectable = &*(*obj as *const Reflector);
trace_reflector(tracer, "refcounted", reflectable);

4
components/script/dom/dedicatedworkerglobalscope.rs
View file

@ -14,7 +14,6 @@ use dom::bindings::error::ErrorResult;
use dom::bindings::global::{GlobalRef, global_root_from_context};
use dom::bindings::inheritance::Castable;
use dom::bindings::js::{Root, RootCollection};
use dom::bindings::refcounted::LiveDOMReferences;
use dom::bindings::reflector::Reflectable;
use dom::bindings::str::DOMString;
use dom::bindings::structuredclone::StructuredCloneData;
@ -298,9 +297,6 @@ impl DedicatedWorkerGlobalScope {
WorkerScriptMsg::Common(CommonScriptMsg::RunnableMsg(_, runnable)) => {
runnable.handler()
},
WorkerScriptMsg::Common(CommonScriptMsg::RefcountCleanup(addr)) => {
LiveDOMReferences::cleanup(addr);
},
WorkerScriptMsg::Common(CommonScriptMsg::CollectReports(reports_chan)) => {
let scope = self.upcast::<WorkerGlobalScope>();
let cx = scope.get_cx();

4
components/script/dom/serviceworkerglobalscope.rs
View file

@ -12,7 +12,6 @@ use dom::bindings::codegen::Bindings::ServiceWorkerGlobalScopeBinding::ServiceWo
use dom::bindings::global::{GlobalRef, global_root_from_context};
use dom::bindings::inheritance::Castable;
use dom::bindings::js::{Root, RootCollection};
use dom::bindings::refcounted::LiveDOMReferences;
use dom::bindings::reflector::Reflectable;
use dom::bindings::str::DOMString;
use dom::eventtarget::EventTarget;
@ -238,9 +237,6 @@ impl ServiceWorkerGlobalScope {
CommonWorker(WorkerScriptMsg::Common(CommonScriptMsg::RunnableMsg(_, runnable))) => {
runnable.handler()
},
CommonWorker(WorkerScriptMsg::Common(CommonScriptMsg::RefcountCleanup(addr))) => {
LiveDOMReferences::cleanup(addr);
},
CommonWorker(WorkerScriptMsg::Common(CommonScriptMsg::CollectReports(reports_chan))) => {
let scope = self.upcast::<WorkerGlobalScope>();
let cx = scope.get_cx();

4
components/script/script_runtime.rs
View file

@ -6,7 +6,7 @@
//! script thread, the dom, and the worker threads.
use dom::bindings::js::{RootCollection, RootCollectionPtr, trace_roots};
use dom::bindings::refcounted::{LiveDOMReferences, TrustedReference, trace_refcounted_objects};
use dom::bindings::refcounted::{LiveDOMReferences, trace_refcounted_objects};
use dom::bindings::trace::trace_traceables;
use dom::bindings::utils::DOM_CALLBACKS;
use js::glue::CollectServoSizes;
@ -35,8 +35,6 @@ pub enum CommonScriptMsg {
/// Requests that the script thread measure its memory usage. The results are sent back via the
/// supplied channel.
CollectReports(ReportsChan),
/// A DOM object's last pinned reference was removed (dispatched to all threads).
RefcountCleanup(TrustedReference),
/// Generic message that encapsulates event handling.
RunnableMsg(ScriptThreadEventCategory, Box<Runnable + Send>),
}

4
components/script/script_thread.rs
View file

@ -31,7 +31,7 @@ use dom::bindings::global::GlobalRef;
use dom::bindings::inheritance::Castable;
use dom::bindings::js::{JS, MutNullableHeap, Root, RootCollection};
use dom::bindings::js::{RootCollectionPtr, RootedReference};
use dom::bindings::refcounted::{LiveDOMReferences, Trusted};
use dom::bindings::refcounted::Trusted;
use dom::bindings::reflector::Reflectable;
use dom::bindings::str::DOMString;
use dom::bindings::trace::JSTraceable;
@ -948,8 +948,6 @@ impl ScriptThread {
runnable.handler()
}
}
MainThreadScriptMsg::Common(CommonScriptMsg::RefcountCleanup(addr)) =>
LiveDOMReferences::cleanup(addr),
MainThreadScriptMsg::Common(CommonScriptMsg::CollectReports(reports_chan)) =>
self.collect_reports(reports_chan),
MainThreadScriptMsg::DOMManipulation(task) =>