Refactor NACK bitrate allocation

webrtc/base/rate_limiter.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_BASE_RATE_LIMITER_H_
+#define WEBRTC_BASE_RATE_LIMITER_H_
+
+#include <limits>
+
+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/base/rate_statistics.h"
+
+namespace webrtc {
+
+class Clock;
+
+// Class used to limit a bitrate, making sure the average does not exceed a
+// maximum as measured over a sliding window. This class is thread safe; all
+// methods will acquire (the same) lock befeore executing.
+class RateLimiter {
+ public:
+  RateLimiter(Clock* clock, int64_t max_window_ms);
+  ~RateLimiter();
+
+  // Try to use rate to send bytes. Returns true on success and if so updates
+  // current rate.
+  bool TryUseRate(size_t packet_size_bytes);
+
+  // Set the maximum bitrate, in bps, that this limiter allows to send.
+  void SetMaxRate(uint32_t max_rate_bps);
+
+  // Set the window size over which to measure the current bitrate.
+  // For example, irt retransmissions, this is typically the RTT.
+  // Returns true on success and false if window_size_ms is out of range.
+  bool SetWindowSize(int64_t window_size_ms);
+
+ private:
+  Clock* const clock_;
+  rtc::CriticalSection lock_;
+  RateStatistics current_rate_ GUARDED_BY(lock_);
+  int64_t window_size_ms_ GUARDED_BY(lock_);
+  uint32_t max_rate_bps_ GUARDED_BY(lock_);
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(RateLimiter);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_BASE_RATE_LIMITER_H_