Create network change notifier.

webrtc/base/networkmonitor.h

+/*
+ *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_NETWORKMONITOR_H_
+#define WEBRTC_BASE_NETWORKMONITOR_H_
+
+#include "webrtc/base/logging.h"
+#include "webrtc/base/scoped_ptr.h"
+#include "webrtc/base/sigslot.h"
+#include "webrtc/base/thread.h"
+
+namespace rtc {
+/*
+ * Receives network-change events via |OnNetworksChanged| and signals the
+ * networks changed event.
+ *
+ * Threading consideration:
+ * It is expected that all upstream operations (from native to Java) are
+ * performed from the worker thread. This includes creating, starting and
+ * stopping the monitor. This avoids the potential race condition when creating
+ * the singleton Java NetworkMonitor class. Downstream operations can be from
+ * any thread, but this class will forward all the downstream operations onto
+ * the worker thread.
+ *
+ * Memory consideration:
+ * NetworkMonitor is owned by the caller (NetworkManager). The global network
+ * monitor factory is owned by the factory itself but needs to be released from
+ * the factory creator by setting it to null.
+ */
+class NetworkMonitor : public MessageHandler, public sigslot::has_slots<> {

[pthatcher1, 2015/10/15 08:11:43]

It seems like this should be called NetworkMontiorBase and it should implement
NetworkMonitorInterface.  

[honghaiz3, 2015/10/15 19:02:42]

Done.

+ public:
+  sigslot::signal0<> SignalNetworksChanged;
+
+  NetworkMonitor() : thread_(Thread::Current()) {}
+  virtual ~NetworkMonitor() {}
+
+  // Creates and starts network monitoring
+  virtual void StartMonitoring() = 0;
+  // Stops and removes network monitoring
+  virtual void StopMonitoring() = 0;

[pthatcher1, 2015/10/15 08:11:43]

Why not just Start() and Stop()?  And I don't think the comments are necessary.

[honghaiz3, 2015/10/15 19:02:42]

Done.

+
+  // Called when it receives a network-change event from the network monitor.

[pthatcher1, 2015/10/15 08:11:43]

The network monitor method is called when it receives a network change from the
network monitor?  That seems confusing.

Why not just say "implementations should call this method on the base when
networks change, and the base will fire SignalNetworksChanged on the right
thread".

[honghaiz3, 2015/10/15 19:02:41]

Done.

+  void OnNetworksChanged();
+
+  void OnMessage(Message* msg) override;
+
+ private:
+  Thread* thread_;
+};
+
+/*
+ * NetworkMonitorFactory creates NetworkMonitors.
+ */
+class NetworkMonitorFactory {
+ public:
+  static void SetFactory(NetworkMonitorFactory* factory);
+  static NetworkMonitorFactory* GetFactory();
+
+  virtual NetworkMonitor* CreateNetworkMonitor() = 0;
+
+  virtual ~NetworkMonitorFactory() {}
+
+ protected:
+  NetworkMonitorFactory() {}
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_NETWORKMONITOR_H_