NackModule2: Rename to NackRequester.

The alternative new name proposed, NackTracker, is already in
use in audio_coding.

Fixed: webrtc:11594
Change-Id: I6a05fafc05fa7ddb18ea4f64886a135e5ef59f7e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/226744
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Markus Handell <handellm@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34539}

modules/video_coding/nack_requester.h

@@ -0,0 +1,168 @@
+/*
+ *  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 MODULES_VIDEO_CODING_NACK_REQUESTER_H_
+#define MODULES_VIDEO_CODING_NACK_REQUESTER_H_
+
+#include <stdint.h>
+
+#include <map>
+#include <set>
+#include <vector>
+
+#include "api/sequence_checker.h"
+#include "api/units/time_delta.h"
+#include "modules/include/module_common_types.h"
+#include "modules/video_coding/histogram.h"
+#include "rtc_base/numerics/sequence_number_util.h"
+#include "rtc_base/task_queue.h"
+#include "rtc_base/task_utils/pending_task_safety_flag.h"
+#include "rtc_base/task_utils/repeating_task.h"
+#include "rtc_base/thread_annotations.h"
+#include "system_wrappers/include/clock.h"
+
+namespace webrtc {
+
+class NackRequesterBase {
+ public:
+  virtual ~NackRequesterBase() = default;
+  virtual void ProcessNacks() = 0;
+};
+
+class NackPeriodicProcessor {
+ public:
+  static constexpr TimeDelta kUpdateInterval = TimeDelta::Millis(20);
+  explicit NackPeriodicProcessor(TimeDelta update_interval = kUpdateInterval);
+  ~NackPeriodicProcessor();
+  void RegisterNackModule(NackRequesterBase* module);
+  void UnregisterNackModule(NackRequesterBase* module);
+
+ private:
+  void ProcessNackModules() RTC_RUN_ON(sequence_);
+
+  const TimeDelta update_interval_;
+  RepeatingTaskHandle repeating_task_ RTC_GUARDED_BY(sequence_);
+  std::vector<NackRequesterBase*> modules_ RTC_GUARDED_BY(sequence_);
+  RTC_NO_UNIQUE_ADDRESS SequenceChecker sequence_;
+};
+
+class ScopedNackPeriodicProcessorRegistration {
+ public:
+  ScopedNackPeriodicProcessorRegistration(NackRequesterBase* module,
+                                          NackPeriodicProcessor* processor);
+  ~ScopedNackPeriodicProcessorRegistration();
+
+ private:
+  NackRequesterBase* const module_;
+  NackPeriodicProcessor* const processor_;
+};
+
+class NackRequester final : public NackRequesterBase {
+ public:
+  NackRequester(TaskQueueBase* current_queue,
+                NackPeriodicProcessor* periodic_processor,
+                Clock* clock,
+                NackSender* nack_sender,
+                KeyFrameRequestSender* keyframe_request_sender);
+  ~NackRequester();
+
+  void ProcessNacks() override;
+
+  int OnReceivedPacket(uint16_t seq_num, bool is_keyframe);
+  int OnReceivedPacket(uint16_t seq_num, bool is_keyframe, bool is_recovered);
+
+  void ClearUpTo(uint16_t seq_num);
+  void UpdateRtt(int64_t rtt_ms);
+
+ private:
+  // Which fields to consider when deciding which packet to nack in
+  // GetNackBatch.
+  enum NackFilterOptions { kSeqNumOnly, kTimeOnly, kSeqNumAndTime };
+
+  // This class holds the sequence number of the packet that is in the nack list
+  // as well as the meta data about when it should be nacked and how many times
+  // we have tried to nack this packet.
+  struct NackInfo {
+    NackInfo();
+    NackInfo(uint16_t seq_num,
+             uint16_t send_at_seq_num,
+             int64_t created_at_time);
+
+    uint16_t seq_num;
+    uint16_t send_at_seq_num;
+    int64_t created_at_time;
+    int64_t sent_at_time;
+    int retries;
+  };
+
+  struct BackoffSettings {
+    BackoffSettings(TimeDelta min_retry, TimeDelta max_rtt, double base);
+    static absl::optional<BackoffSettings> ParseFromFieldTrials();
+
+    // Min time between nacks.
+    const TimeDelta min_retry_interval;
+    // Upper bound on link-delay considered for exponential backoff.
+    const TimeDelta max_rtt;
+    // Base for the exponential backoff.
+    const double base;
+  };
+
+  void AddPacketsToNack(uint16_t seq_num_start, uint16_t seq_num_end)
+      RTC_EXCLUSIVE_LOCKS_REQUIRED(worker_thread_);
+
+  // Removes packets from the nack list until the next keyframe. Returns true
+  // if packets were removed.
+  bool RemovePacketsUntilKeyFrame()
+      RTC_EXCLUSIVE_LOCKS_REQUIRED(worker_thread_);
+  std::vector<uint16_t> GetNackBatch(NackFilterOptions options)
+      RTC_EXCLUSIVE_LOCKS_REQUIRED(worker_thread_);
+
+  // Update the reordering distribution.
+  void UpdateReorderingStatistics(uint16_t seq_num)
+      RTC_EXCLUSIVE_LOCKS_REQUIRED(worker_thread_);
+
+  // Returns how many packets we have to wait in order to receive the packet
+  // with probability |probabilty| or higher.
+  int WaitNumberOfPackets(float probability) const
+      RTC_EXCLUSIVE_LOCKS_REQUIRED(worker_thread_);
+
+  TaskQueueBase* const worker_thread_;
+  Clock* const clock_;
+  NackSender* const nack_sender_;
+  KeyFrameRequestSender* const keyframe_request_sender_;
+
+  // TODO(philipel): Some of the variables below are consistently used on a
+  // known thread (e.g. see |initialized_|). Those probably do not need
+  // synchronized access.
+  std::map<uint16_t, NackInfo, DescendingSeqNumComp<uint16_t>> nack_list_
+      RTC_GUARDED_BY(worker_thread_);
+  std::set<uint16_t, DescendingSeqNumComp<uint16_t>> keyframe_list_
+      RTC_GUARDED_BY(worker_thread_);
+  std::set<uint16_t, DescendingSeqNumComp<uint16_t>> recovered_list_
+      RTC_GUARDED_BY(worker_thread_);
+  video_coding::Histogram reordering_histogram_ RTC_GUARDED_BY(worker_thread_);
+  bool initialized_ RTC_GUARDED_BY(worker_thread_);
+  int64_t rtt_ms_ RTC_GUARDED_BY(worker_thread_);
+  uint16_t newest_seq_num_ RTC_GUARDED_BY(worker_thread_);
+
+  // Adds a delay before send nack on packet received.
+  const int64_t send_nack_delay_ms_;
+
+  const absl::optional<BackoffSettings> backoff_settings_;
+
+  ScopedNackPeriodicProcessorRegistration processor_registration_;
+
+  // Used to signal destruction to potentially pending tasks.
+  ScopedTaskSafety task_safety_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_NACK_REQUESTER_H_