Fabric: ShadowNodeFamily, maintaining a pointer to a parent family

Summary:
One of the core feature of ShadowNodeFamily is having a pointer to a parent family. This diff implements it.
I don't think there is a hard retain cycle there, but for more lean memory usage we use weak_ptr here.

Reviewed By: JoshuaGross

Differential Revision: D14416948

fbshipit-source-id: 05fd2c4833146f007228363b1d958776b4a2a9cf

ReactCommon/fabric/core/shadownode/ShadowNode.cpp

@@ -46,6 +46,10 @@ ShadowNode::ShadowNode(
       revision_(1) {
   assert(props_);
   assert(children_);
+
+  for (const auto &child : *children_) {
+    child->family_->setParent(family_);
+  }
 }
 
 ShadowNode::ShadowNode(
@@ -71,6 +75,12 @@ ShadowNode::ShadowNode(
 
   assert(props_);
   assert(children_);
+
+  if (fragment.children) {
+    for (const auto &child : *children_) {
+      child->family_->setParent(family_);
+    }
+  }
 }
 
 UnsharedShadowNode ShadowNode::clone(const ShadowNodeFragment &fragment) const {
@@ -139,6 +149,8 @@ void ShadowNode::appendChild(const SharedShadowNode &child) {
   auto nonConstChildren =
       std::const_pointer_cast<SharedShadowNodeList>(children_);
   nonConstChildren->push_back(child);
+
+  child->family_->setParent(family_);
 }
 
 void ShadowNode::replaceChild(
@@ -161,6 +173,8 @@ void ShadowNode::replaceChild(
 
   std::replace(
       nonConstChildren->begin(), nonConstChildren->end(), oldChild, newChild);
+
+  newChild->family_->setParent(family_);
 }
 
 void ShadowNode::setLocalData(const SharedLocalData &localData) {

ReactCommon/fabric/core/shadownode/ShadowNodeFamily.cpp

@@ -20,5 +20,15 @@ ShadowNodeFamily::ShadowNodeFamily(
       eventEmitter_(eventEmitter),
       componentDescriptor_(componentDescriptor) {}
 
+void ShadowNodeFamily::setParent(ShadowNodeFamily::Shared const &parent) const {
+  assert(parent_.lock() == nullptr || parent_.lock() == parent);
+  if (hasParent_) {
+    return;
+  }
+
+  parent_ = parent;
+  hasParent_ = true;
+}
+
 } // namespace react
 } // namespace facebook

ReactCommon/fabric/core/shadownode/ShadowNodeFamily.h

@@ -32,6 +32,13 @@ class ShadowNodeFamily {
       SharedEventEmitter const &eventEmitter,
       ComponentDescriptor const &componentDescriptor);
 
+  /*
+   * Sets the parent.
+   * This is not techically thread-safe, but practically it mutates the object
+   * only once (and the model enforces that this first call is not concurent).
+   */
+  void setParent(ShadowNodeFamily::Shared const &parent) const;
+
  private:
   friend ShadowNode;
 
@@ -55,6 +62,17 @@ class ShadowNodeFamily {
    * type.
    */
   ComponentDescriptor const &componentDescriptor_;
+
+  /*
+   * Points to a family of all parent nodes of all nodes of the family.
+   */
+  mutable ShadowNodeFamily::Weak parent_{};
+
+  /*
+   * Represents a case where `parent_` is `nullptr`.
+   * For optimization purposes only.
+   */
+  mutable bool hasParent_{false};
 };
 
 } // namespace react