components/performance_manager/graph/node_base.h

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_PERFORMANCE_MANAGER_GRAPH_NODE_BASE_H_
#define COMPONENTS_PERFORMANCE_MANAGER_GRAPH_NODE_BASE_H_

#include <stdint.h>

#include "base/check_op.h"
#include "base/memory/raw_ptr.h"
#include "base/sequence_checker.h"
#include "components/performance_manager/graph/graph_impl.h"
#include "components/performance_manager/graph/properties.h"
#include "components/performance_manager/public/graph/node_state.h"
#include "components/performance_manager/public/graph/node_type.h"

namespace performance_manager {

class Node;

// NodeBase implements shared functionality among different types of graph
// nodes. A specific type of graph node will derive from this class and can
// override shared functionality when needed.
// All node classes allow construction on one sequence and subsequent use from
// another sequence.
// All methods not documented otherwise are single-threaded.
class NodeBase {
 public:
  // Used as a unique key to safely allow downcasting from a public node type
  // to NodeBase via "GetImplType" and "GetImpl". The implementations are
  // provided by PublicNodeImpl below.
  static const uintptr_t kNodeBaseType;

  NodeBase();

  NodeBase(const NodeBase&) = delete;
  NodeBase& operator=(const NodeBase&) = delete;

  virtual ~NodeBase();

  // May be called on any sequence.
  NodeTypeEnum GetNodeType() const { return ToNode()->GetNodeType(); }

  // The state of this node.
  NodeState GetNodeState() const {
    DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
    if (!graph_) {
      return NodeState::kNotInGraph;
    }
    return graph_->GetNodeState(this);
  }

  // Returns the graph that contains this node. Only valid after JoinGraph() and
  // before LeaveGraph().
  GraphImpl* graph() const {
    DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
    DCHECK(graph_);
    return graph_;
  }

  // Helper functions for casting from a node type to its underlying NodeBase.
  // This CHECKs that the cast is valid. These functions work happily with
  // public and private node class inputs.
  static const NodeBase* FromNode(const Node* node);
  static NodeBase* FromNode(Node* node);

  // For converting from NodeBase to Node. This is implemented by
  // TypedNodeBase.
  virtual const Node* ToNode() const = 0;

  // Satisfies part of the contract expected by ObservedProperty.
  // GetObservers is implemented by TypedNodeImpl.
  bool CanSetProperty() const;
  bool CanSetAndNotifyProperty() const;

 protected:
  friend class GraphImpl;

  // Helper function for TypedNodeBase to access the list of typed observers
  // stored in the graph.
  template <typename Observer>
  const GraphImpl::ObserverList<Observer>& GetObservers(
      const GraphImpl* graph) const {
    DCHECK(CanSetAndNotifyProperty());
    return graph->GetObservers<Observer>();
  }

  // Node lifecycle:

  // Step 0: A node is constructed. Node state is kNotInGraph. Outgoing edges
  // are set but not publicly visible.

  // Step 1:
  // Initializes the `graph_` pointer. Node must be in the kNotInGraph state.
  void SetGraphPointer(GraphImpl* graph);

  // Step 2:
  // Node enters kInitializingNotInGraph state: nodes may modify their
  // properties that don't affect the graph topology but *not* cause any
  // notifications to be emitted that refer to the node, since public observers
  // have not been notified that the node was added to the graph via
  // OnBeforeNodeAdded and OnNodeAdded yet.

  // Called after `graph_` is set, a good opportunity to initialize node state.
  virtual void OnInitializingProperties();

  // Step 3:
  // OnBeforeNodeAdded notifications are dispatched. The public observer method
  // can read and update the node state, but sees no incoming or outgoing edges.
  // The graph is in a consistent state that doesn't include this node.

  // Step 4:
  // Node enters kInitializingEdges state: nodes may modify their properties
  // that link to other nodes but *not* cause any notifications to be emitted
  // that refer to the node, since public observers have not been notified that
  // the node was added to the graph via OnNodeAdded yet.

  // Called after properties are initialized, for nodes to update incoming edges
  // to fully join the graph.
  virtual void OnInitializingEdges();

  // Step 5:
  // Node enters kJoiningGraph state: the node must not be modified, since
  // observers will now be notified of its initial state in the graph, and each
  // observer should see the same state.

  // OnNodeAdded notifications are dispatched.

  // Step 6:
  // Node enters kActiveInGraph state: the node may make property changes, and
  // these changes may cause notifications to be dispatched.

  // Called just after sending OnNodeAdded notifications, for nodes to perform
  // initialization that causes notifications to be dispatched. For example,
  // this could be used to set up an "opener" relationship between a PageNode
  // and FrameNode: when OnPageNodeAdded() was called, the graph was in the
  // valid state where both FrameNode and PageNode exist but the PageNode has
  // no opener. Then this function sets the FrameNode as the opener and sends
  // the OnOpenerFrameNodeChanged notification.
  virtual void OnAfterJoiningGraph();

  // The node lives in the graph normally at this point, in the kActiveInGraph
  // state.

  // Step 7:
  // Called just before sending OnBeforeNodeRemoved notifications, for nodes to
  // perform cleanup that causes notifications to be dispatched. This must leave
  // the node and the graph in a consistent state since the node is still in the
  // graph. For example if this is used to sever the "opener" relationship
  // between a PageNode and a FrameNode, it must send the
  // OnOpenerFrameNodeChanged notification, and leave the PageNode and FrameNode
  // in the valid state they would have when the page has no opener.
  virtual void OnBeforeLeavingGraph();

  // Step 8:
  // Node enters kLeavingGraph state: the node must not be modified, since it's
  // about to be deleted. Observers will commonly use OnBeforeNodeRemoved
  // notifications to clean up, and each observer should see the same state.

  // OnBeforeNodeRemoved notifications are dispatched.

  // Step 9:
  // Node enters kUninitializingEdges state: nodes may modify their properties
  // that link to other nodes but *not* cause any notifications to be emitted
  // that refer to the node, since public observers have already been notified
  // that the node is being removed from the graph via OnBeforeNodeRemoved.

  // Called while leaving `graph_`, to sever the node from the graph by updating
  // incoming edges.
  virtual void OnUninitializingEdges();

  // Step 10:
  // Node enters kLeftGraph state: the node must not be modified, since it's
  // about to be deleted. Any property changes would only be visible to other
  // OnNodeRemoved observers, and their effects shouldn't depend on the order
  // that observers are triggered.

  // OnNodeRemoved notifications are dispatched. The public observer method sees
  // the node's final properties but no incoming or outgoing edges. The graph is
  // in a consistent state that doesn't include this node.

  // Step 11:
  // Called after the node's edges have been severed from the graph, a good
  // opportunity to uninitialize node state. This is a pure virtual since almost
  // all node classes must implement it to destroy private node-attached data.
  virtual void CleanUpNodeState() = 0;

  // Step 12:
  // Resets the graph pointer. The node is in the kLeftGraph state during this
  // call, and will be in the kNotInGraph state immediately afterwards.
  void ClearGraphPointer();

  // Assigned when SetGraphPointer() is called, up until ClearGraphPointer() is
  // called, where it is reset to null.
  raw_ptr<GraphImpl> graph_ GUARDED_BY_CONTEXT(sequence_checker_) = nullptr;

  SEQUENCE_CHECKER(sequence_checker_);
};

// Helper for implementing the Node parent of a PublicNodeClass.
template <class NodeImplClass, class PublicNodeClass>
class PublicNodeImpl : public PublicNodeClass {
 public:
  // Node implementation:
  Graph* GetGraph() const override {
    return static_cast<const NodeImplClass*>(this)->graph();
  }
  uintptr_t GetImplType() const override { return NodeBase::kNodeBaseType; }
  const void* GetImpl() const override {
    // This exposes NodeBase, so that we can complete the triangle of casting
    // between all views of a node: NodeBase, FooNodeImpl, and FooNode.
    return static_cast<const NodeBase*>(
        static_cast<const NodeImplClass*>(this));
  }
};

template <class NodeImplClass, class NodeClass, class NodeObserverClass>
class TypedNodeBase : public NodeBase {
 public:
  using ObservedProperty =
      ObservedPropertyImpl<NodeImplClass, NodeClass, NodeObserverClass>;

  TypedNodeBase() = default;

  TypedNodeBase(const TypedNodeBase&) = delete;
  TypedNodeBase& operator=(const TypedNodeBase&) = delete;

  // Helper functions for casting from NodeBase to a concrete node type. This
  // CHECKs that the cast is valid.
  static const NodeImplClass* FromNodeBase(const NodeBase* node) {
    CHECK_EQ(NodeImplClass::Type(), node->GetNodeType());
    return static_cast<const NodeImplClass*>(node);
  }
  static NodeImplClass* FromNodeBase(NodeBase* node) {
    CHECK_EQ(NodeImplClass::Type(), node->GetNodeType());
    return static_cast<NodeImplClass*>(node);
  }

  // Helper functions for casting from a public node type to the private impl.
  // This also casts away const correctness, as it is intended to be used by
  // impl code that uses the public observer interface for a node type, where
  // all notifications are delivered with a const node pointer. This CHECKs that
  // the cast is valid.
  static NodeImplClass* FromNode(const Node* node) {
    NodeBase* node_base = const_cast<NodeBase*>(NodeBase::FromNode(node));
    return FromNodeBase(node_base);
  }

  // Convenience accessor to the per-node-class list of observers that is stored
  // in the graph. Satisfies the contract expected by ObservedProperty.
  const GraphImpl::ObserverList<NodeObserverClass>& GetObservers() const {
    // Mediate through NodeBase, as it's the class that is friended by the
    // GraphImpl in order to provide access.
    return NodeBase::GetObservers<NodeObserverClass>(graph());
  }

  const Node* ToNode() const override {
    return static_cast<const NodeImplClass*>(this);
  }
};

}  // namespace performance_manager

#endif  // COMPONENTS_PERFORMANCE_MANAGER_GRAPH_NODE_BASE_H_