Bug 1736604 - Part 1: Replace sweeping with tracing weak edges in WeakRef implementation r=sfink

Differential Revision: https://phabricator.services.mozilla.com/D128901

js/src/builtin/WeakRefObject.cpp

@@ -298,23 +298,27 @@ void GCRuntime::traceKeptObjects(JSTracer* trc) {
 
 }  // namespace gc
 
-void WeakRefMap::sweep(gc::StoreBuffer* sbToLock) {
+static WeakRefObject* UnwrapWeakRef(JSObject* obj) {
+  MOZ_ASSERT(!JS_IsDeadWrapper(obj));
+  obj = UncheckedUnwrapWithoutExpose(obj);
+  return &obj->as<WeakRefObject>();
+}
+
+void WeakRefMap::traceWeak(JSTracer* trc, gc::StoreBuffer* sbToLock) {
   mozilla::Maybe<typename Base::Enum> e;
   for (e.emplace(*this); !e->empty(); e->popFront()) {
     // If target is dying, clear the target field of all weakRefs, and remove
     // the entry from the map.
-    if (JS::GCPolicy<HeapPtrObject>::needsSweep(&e->front().mutableKey())) {
+    auto result =
+        TraceWeakEdge(trc, &e->front().mutableKey(), "WeakRef target");
+    if (result.isDead()) {
       for (JSObject* obj : e->front().value()) {
-        MOZ_ASSERT(!JS_IsDeadWrapper(obj));
-        obj = UncheckedUnwrapWithoutExpose(obj);
-
-        WeakRefObject* weakRef = &obj->as<WeakRefObject>();
-        weakRef->clearTarget();
+        UnwrapWeakRef(obj)->clearTarget();
       }
       e->removeFront();
     } else {
       // Update the target field after compacting.
-      e->front().value().sweep(e->front().mutableKey());
+      e->front().value().traceWeak(trc, result.finalTarget());
     }
   }
 
@@ -326,20 +330,15 @@ void WeakRefMap::sweep(gc::StoreBuffer* sbToLock) {
 
 // Like GCVector::sweep, but this method will also update the target in every
 // weakRef in this GCVector.
-void WeakRefHeapPtrVector::sweep(HeapPtrObject& target) {
+void WeakRefHeapPtrVector::traceWeak(JSTracer* trc, JSObject* target) {
   HeapPtrObject* src = begin();
   HeapPtrObject* dst = begin();
   while (src != end()) {
-    bool needsSweep = JS::GCPolicy<HeapPtrObject>::needsSweep(src);
-    JSObject* obj = UncheckedUnwrapWithoutExpose(*src);
-    MOZ_ASSERT(!JS_IsDeadWrapper(obj));
-
-    WeakRefObject* weakRef = &obj->as<WeakRefObject>();
-
-    if (needsSweep) {
-      weakRef->clearTarget();
+    auto result = TraceWeakEdge(trc, src, "WeakRef");
+    if (result.isDead()) {
+      UnwrapWeakRef(result.initialTarget())->clearTarget();
     } else {
-      weakRef->setTargetUnbarriered(target.get());
+      UnwrapWeakRef(result.finalTarget())->setTargetUnbarriered(target);
 
       if (src != dst) {
         *dst = std::move(*src);

js/src/gc/Compacting.cpp

@@ -457,7 +457,7 @@ void Zone::prepareForCompacting() {
 void GCRuntime::sweepZoneAfterCompacting(MovingTracer* trc, Zone* zone) {
   MOZ_ASSERT(zone->isCollecting());
   traceWeakFinalizationRegistryEdges(trc, zone);
-  zone->weakRefMap().sweep(&storeBuffer());
+  zone->weakRefMap().traceWeak(trc, &storeBuffer());
 
   zone->traceWeakMaps(trc);
 

js/src/gc/Sweeping.cpp

@@ -1276,7 +1276,7 @@ bool UniqueIdGCPolicy::traceWeak(JSTracer* trc, Cell** keyp, uint64_t* valuep) {
 void GCRuntime::sweepWeakRefs() {
   for (SweepGroupZonesIter zone(this); !zone.done(); zone.next()) {
     AutoSetThreadIsSweeping threadIsSweeping(zone);
-    zone->weakRefMap().sweep(&storeBuffer());
+    zone->weakRefMap().traceWeak(&sweepingTracer, &storeBuffer());
   }
 }
 

js/src/gc/Zone.h

@@ -116,7 +116,7 @@ class WeakRefHeapPtrVector
   using GCVector::GCVector;
 
   // call in compacting, to update the target in each WeakRefObject.
-  void sweep(js::HeapPtrObject& target);
+  void traceWeak(JSTracer* trc, JSObject* target);
 };
 
 // WeakRefMap is a per-zone GCHashMap, which maps from the target of the JS
@@ -128,7 +128,7 @@ class WeakRefMap
   using GCHashMap::GCHashMap;
   using Base = GCHashMap<HeapPtrObject, WeakRefHeapPtrVector,
                          MovableCellHasher<HeapPtrObject>, ZoneAllocPolicy>;
-  void sweep(gc::StoreBuffer* sbToLock);
+  void traceWeak(JSTracer* trc, gc::StoreBuffer* sbToLock);
 };
 
 }  // namespace js