chromium/components/performance_manager/graph/properties.h

// Copyright 2019 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_PROPERTIES_H_
#define COMPONENTS_PERFORMANCE_MANAGER_GRAPH_PROPERTIES_H_

#include <utility>

#include "base/check.h"
#include "components/performance_manager/public/graph/node_state.h"

namespace performance_manager {

// Helper classes for setting properties and invoking observer callbacks based
// on the value change. This is templated on the observer type to allow
// easy testing.
//
// Objects of NodeImplType are expected to fulfill the contract:
//
//   IterableCollection GetObservers() const;
//   bool NodeImplType::CanSetProperty() const;
//   bool NodeImplType::CanSetAndNotifyProperty() const;
//
// These are used in DCHECKs to assert that properties are only being modified
// at appropriate moments. If your code is blowing up in one of these DCHECKS
// you are trying to change a property while a node is being added or removed
// from the graph. When adding to the graph property changes should be done in a
// separate posted task. When removing from the graph, they should simply not be
// done. See class comments on node observers, NodeState, and NodeBase for full
// details.
template <typename NodeImplType, typename NodeType, typename ObserverType>
class ObservedPropertyImpl { … };

}  // namespace performance_manager

#endif  // COMPONENTS_PERFORMANCE_MANAGER_GRAPH_PROPERTIES_H_