[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/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 {
+
+class CoordinationUnitImpl;
+
+// 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 CoordinationUnitmanagerObserver will only call

[Zhen Wang, 2017/06/15 20:07:52]

s/CoordinationUnitmanagerObserver/CoordinationUnitManager ?

[matthalp, 2017/06/16 00:01:26]

Yes. Thank you for catching this.

+  // CoordinationUnitGraphObserver::CoordinationUnitCreated when the
+  // CoordinationUnit's CoordinationUnitID.type matches filter.
+  explicit CoordinationUnitGraphObserver(CoordinationUnitType filter);
+  virtual ~CoordinationUnitGraphObserver();
+
+  CoordinationUnitType filter() const { return filter_; }

[Zhen Wang, 2017/06/15 20:07:52]

Instead of exposing filter type, how about using something like ShouldObserve()?
And inside the function, it actually checks the filter type.

The reason is that if the filter type is invalid, it indicates that we do not
filter anything. When the manager does the check, it is not intuitive that
"invalid" actually means "do not filter".

[matthalp, 2017/06/16 00:01:26]

That is definitely cleaner -- done.

+
+  // Called whenever any new CoordinationUnit of any type is created. Note that

[Zhen Wang, 2017/06/15 20:07:52]

This is only called when it matches the filter, right. And if the filter is
kInvalidType, it is called for any type. If we switch to use ShouldObserve() or
something similar, we can just say this function is only called when it should
observe this CU.

[matthalp, 2017/06/16 00:01:27]

Done. Please let me know if the new comments are sufficient.

+  // this will be called after any specialized *CoordinationUnitCreated (e.g.
+  // FrameCoordinationUnitCreation, etc.) is called.
+  virtual void CoordinationUnitCreated(
+      CoordinationUnitImpl* coordination_unit) {}
+
+ private:
+  CoordinationUnitType filter_;
+
+  DISALLOW_COPY_AND_ASSIGN(CoordinationUnitGraphObserver);
+};
+
+}  // namespace resource_coordinator
+
+#endif  // SERVICES_RESOURCE_COORDINATOR_COORDINATION_UNIT_COORDINATION_UNIT_GRAPH_OBSERVER_H_