Probing: Add support for exponential startup probing

webrtc/modules/congestion_controller/probe_controller.h

+/*
+ *  Copyright (c) 2016 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_MODULES_CONGESTION_CONTROLLER_PROBE_CONTROLLER_H_
+#define WEBRTC_MODULES_CONGESTION_CONTROLLER_PROBE_CONTROLLER_H_
+
+#include <initializer_list>
+
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/common_types.h"
+#include "webrtc/modules/pacing/paced_sender.h"
+
+namespace webrtc {
+
+class Clock;
+
+// This class controls initiation of probing to estimate initial channel
+// capacity. There is also support for probing during a session when max
+// bitrate is adjusted by an application.
+class ProbeController {
+ public:
+  ProbeController(PacedSender* pacer, Clock* clock);
+
+  void SetBitrates(int min_bitrate_bps,
+                   int start_bitrate_bps,
+                   int max_bitrate_bps);
+  void SetEstimatedBitrate(int bitrate_bps);
+
+ private:
+  void InitiateProbing(std::initializer_list<int> bitrates_to_probe,

[philipel, 2016/09/09 08:59:09]

What is the reason we use an std::initializer_list instead of a std::vector?

[Irfan, 2016/09/12 06:40:40]

It is a light weight proxy for {} list. std::vector actually takes an
std::initializer_list and constructs a vector. Since we just need an
unmodifiable list, this suffices.

+                       int min_bitrate_to_probe_further_bps)
+      EXCLUSIVE_LOCKS_REQUIRED(critsect_);
+  enum class State {
+    // Initial state where no probing has been triggered yet.
+    kInit,
+    // Waiting for probing results to continue further probing.
+    kWaitingForProbingResult,
+    // Probing is complete.
+    kProbingComplete,
+  };
+  rtc::CriticalSection critsect_;
+  PacedSender* const pacer_;
+  Clock* const clock_;
+  State state_ GUARDED_BY(critsect_);
+  int min_bitrate_to_probe_further_bps_ GUARDED_BY(critsect_);
+  int64_t time_last_probing_initiated_ms_ GUARDED_BY(critsect_);
+  int estimated_bitrate_bps_ GUARDED_BY(critsect_);
+  int max_bitrate_bps_ GUARDED_BY(critsect_);
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(ProbeController);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_CONGESTION_CONTROLLER_PROBE_CONTROLLER_H_