Notify NQE of TCP RTT values

net/base/socket_performance_watcher.h

 // Copyright 2015 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 NET_BASE_SOCKET_PERFORMANCE_WATCHER_H_
 #define NET_BASE_SOCKET_PERFORMANCE_WATCHER_H_
 
+#include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "net/base/net_export.h"
 #include "net/base/socket_performance_watcher_factory.h"
 
 namespace base {
 class TimeDelta;
 }  // namespace base
 
 namespace net {
 
 // SocketPerformanceWatcher is the base class for recording and aggregating
 // socket statistics.
 class NET_EXPORT_PRIVATE SocketPerformanceWatcher {
  public:
   // |socket_performance_watcher_factory| is the factory that constructed
   // |this| watcher.
   SocketPerformanceWatcher(
       const SocketPerformanceWatcherFactory::Protocol protocol,
       SocketPerformanceWatcherFactory* socket_performance_watcher_factory);
 
   virtual ~SocketPerformanceWatcher();
 
   // Called when updated transport layer RTT information is available. This
   // must be the transport layer RTT from this device to the remote transport
   // layer endpoint. This method is called immediately after the observation is
   // made, hence no timestamp.
-  void OnUpdatedRTTAvailable(const base::TimeDelta& rtt) const;
+  void OnUpdatedRTTAvailable(const base::TimeDelta& rtt);
+
+  // Returns true if |this| should be notified of the updated RTT value.
+  bool ShouldNotifyUpdatedRTT() const WARN_UNUSED_RESULT;

[Ryan Sleevi, 2016/03/04 01:38:38]

I still don't know how to make sense of this - or how to use it properly.

Are you saying that every call should be

if (ShouldNotifyUpdatedRTT())
  OnUpdatedRTTAvailable(...) ?

Or something else?

If that's correct (and it looks like it is)

// Returns |true| if the current SocketPerformanceWatcher is interested
// in receiving a new RTT estimate (via OnUpdatedRTTAvailable).
// Callers may use this to avoid doing expensive work computing the
// RTT when the SocketPerformanceWatcher is not interested in such
// updates.

That feels klunkily worded, but maybe that gets more to the "Here's how you can
hold this / why this exists" sort of explanation.

[tbansal1, 2016/03/04 02:37:53]

Yes, that's what I meant.
Done.

+
+  // Resets the internal state of this SocketPerformanceWatcher in preparation
+  // for observing a new socket.
+  // Note: The new socket must share the same protocol as the previously
+  // observed socket.
+  void Reset();
 
  private:
   // Transport layer protocol used by the socket that |this| is watching.
   const SocketPerformanceWatcherFactory::Protocol protocol_;
 
+  // Time when the last RTT notification was received.
+  base::TimeTicks last_rtt_notification_;
+
+  // Minimum time interval between two successive OnUpdatedRTTAvailable
+  // notifications to |this|.
+  const base::TimeDelta rtt_notification_interval_;
+
   // |socket_performance_watcher_factory_| is the factory that created
   // |this| watcher.
   SocketPerformanceWatcherFactory* socket_performance_watcher_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SocketPerformanceWatcher);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_SOCKET_PERFORMANCE_WATCHER_H_