Shape *
PropertyTree::lookupChild(ThreadSafeContext *cx, Shape *parent, const StackShape &child)
{
/* Keep this in sync with the logic of getChild above. */
Shape *shape = nullptr;
JS_ASSERT(parent);
KidsPointer *kidp = &parent->kids;
if (kidp->isShape()) {
Shape *kid = kidp->toShape();
if (kid->matches(child))
shape = kid;
} else if (kidp->isHash()) {
if (KidsHash::Ptr p = kidp->toHash()->readonlyThreadsafeLookup(child))
shape = *p;
} else {
return nullptr;
}
#if defined(JSGC_INCREMENTAL) && defined(DEBUG)
if (shape) {
JS::Zone *zone = shape->arenaHeader()->zone;
JS_ASSERT(!zone->needsIncrementalBarrier());
JS_ASSERT(!(zone->isGCSweeping() && !shape->isMarked() &&
!shape->arenaHeader()->allocatedDuringIncremental));
}
#endif
return shape;
}
Shape *
PropertyTree::getChild(ExclusiveContext *cx, Shape *parentArg, StackShape &unrootedChild)
{
RootedShape parent(cx, parentArg);
JS_ASSERT(parent);
Shape *existingShape = nullptr;
/*
* The property tree has extremely low fan-out below its root in
* popular embeddings with real-world workloads. Patterns such as
* defining closures that capture a constructor's environment as
* getters or setters on the new object that is passed in as
* |this| can significantly increase fan-out below the property
* tree root -- see bug 335700 for details.
*/
KidsPointer *kidp = &parent->kids;
if (kidp->isShape()) {
Shape *kid = kidp->toShape();
if (kid->matches(unrootedChild))
existingShape = kid;
} else if (kidp->isHash()) {
if (KidsHash::Ptr p = kidp->toHash()->lookup(unrootedChild))
existingShape = *p;
} else {
/* If kidp->isNull(), we always insert. */
}
#ifdef JSGC_INCREMENTAL
if (existingShape) {
JS::Zone *zone = existingShape->zone();
if (zone->needsIncrementalBarrier()) {
/*
* We need a read barrier for the shape tree, since these are weak
* pointers.
*/
Shape *tmp = existingShape;
MarkShapeUnbarriered(zone->barrierTracer(), &tmp, "read barrier");
JS_ASSERT(tmp == existingShape);
} else if (zone->isGCSweeping() && !existingShape->isMarked() &&
!existingShape->arenaHeader()->allocatedDuringIncremental)
{
/*
* The shape we've found is unreachable and due to be finalized, so
* remove our weak reference to it and don't use it.
*/
JS_ASSERT(parent->isMarked());
parent->removeChild(existingShape);
existingShape = nullptr;
}
}
#endif
if (existingShape)
return existingShape;
RootedGeneric<StackShape*> child(cx, &unrootedChild);
Shape *shape = newShape(cx);
if (!shape)
return nullptr;
new (shape) Shape(*child, parent->numFixedSlots());
if (!insertChild(cx, parent, shape))
return nullptr;
return shape;
}