[GRC] Coordination Unit Graph Observer

services/resource_coordinator/coordination_unit/coordination_unit_graph_observer.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SERVICES_RESOURCE_COORDINATOR_COORDINATION_UNIT_COORDINATION_UNIT_GRAPH_OBSERVER_H_
+#define SERVICES_RESOURCE_COORDINATOR_COORDINATION_UNIT_COORDINATION_UNIT_GRAPH_OBSERVER_H_
+
+#include <memory>
+#include <unordered_map>
+
+#include "base/macros.h"
+#include "services/resource_coordinator/coordination_unit/coordination_unit_impl.h"
+#include "services/resource_coordinator/public/cpp/coordination_unit_id.h"
+#include "services/resource_coordinator/public/cpp/coordination_unit_types.h"
+#include "services/resource_coordinator/public/interfaces/coordination_unit.mojom.h"
+
+namespace resource_coordinator {
+
+// An observer API for the CoordinationUnitGraph maintained by GRC.
+//
+// Observers are instantiated when the resource_coordinator serivce
+// is created and are destroyed when the resource_coordinator service
+// is destroyed. Therefore observers are guaranteed to be alive before
+// any coordination unit is created and will be alive after any
+// coordination unit is destroyed. Additionally, any
+// Coordination Unit reachable within a callback will always be
+// initialized and valid.
+//
+// To create and install a new observer:
+//   (1) derive from this class
+//   (2) register in CoordinationUnitManager::RegisterObserver
+//       inside of CoordinationUnitManager::CoordinationUnitManager
+//
+class CoordinationUnitGraphObserver {
+ public:
+  CoordinationUnitGraphObserver();
+  // The CoordinationUnitGraphObserver will only call
+  // CoordinationUnitGraphObserver::CoordinationUnitCreated when the
+  // CoordinationUnit's CoordinationUnitID.type matches filter.
+  explicit CoordinationUnitGraphObserver(CoordinationUnitType filter);
+  virtual ~CoordinationUnitGraphObserver();
+
+  // Determines whether or not OnCoordinationUnitCreated should be
+  // invoked on the newly created CoordinationUnit.
+  bool ShouldObserve(CoordinationUnitImpl* coordination_unit);
+
+  // Called whenever any new CoordinationUnit of interest is created
+  // (i.e. ShouldObserve evaluates to true).
+  virtual void OnCoordinationUnitCreated(
+      CoordinationUnitImpl* coordination_unit) {}
+
+ protected:
+  CoordinationUnitType filter_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CoordinationUnitGraphObserver);
+};
+
+}  // namespace resource_coordinator
+
+#endif  // SERVICES_RESOURCE_COORDINATOR_COORDINATION_UNIT_COORDINATION_UNIT_GRAPH_OBSERVER_H_