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https://github.com/ZLMediaKit/ZLMediaKit.git
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92e7d8837e
如果一组丢包，通过多个nack发送，那么多次执行blp_vec.resize(16, false)并不会重置元素值，这会导致blp_vec的丢包状态错乱，从而产生一些不必要的重传请求。
285 lines
8.1 KiB
C++
285 lines
8.1 KiB
C++
/*
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* Copyright (c) 2016 The ZLMediaKit project authors. All Rights Reserved.
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*
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* This file is part of ZLMediaKit(https://github.com/ZLMediaKit/ZLMediaKit).
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*
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* Use of this source code is governed by MIT license that can be found in the
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* LICENSE file in the root of the source tree. All contributing project authors
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* may be found in the AUTHORS file in the root of the source tree.
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*/
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#include "Nack.h"
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using namespace std;
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using namespace toolkit;
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namespace mediakit {
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static constexpr uint32_t kMaxNackMS = 5 * 1000;
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static constexpr uint32_t kRtpCacheCheckInterval = 100;
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void NackList::pushBack(RtpPacket::Ptr rtp) {
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auto seq = rtp->getSeq();
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_nack_cache_seq.emplace_back(seq);
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_nack_cache_pkt.emplace(seq, std::move(rtp));
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if (++_cache_ms_check < kRtpCacheCheckInterval) {
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return;
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}
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_cache_ms_check = 0;
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while (getCacheMS() >= kMaxNackMS) {
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// 需要清除部分nack缓存
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popFront();
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}
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}
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void NackList::forEach(const FCI_NACK &nack, const function<void(const RtpPacket::Ptr &rtp)> &func) {
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auto seq = nack.getPid();
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for (auto bit : nack.getBitArray()) {
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if (bit) {
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// 丢包
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RtpPacket::Ptr *ptr = getRtp(seq);
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if (ptr) {
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func(*ptr);
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}
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}
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++seq;
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}
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}
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void NackList::popFront() {
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if (_nack_cache_seq.empty()) {
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return;
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}
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_nack_cache_pkt.erase(_nack_cache_seq.front());
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_nack_cache_seq.pop_front();
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}
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RtpPacket::Ptr *NackList::getRtp(uint16_t seq) {
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auto it = _nack_cache_pkt.find(seq);
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if (it == _nack_cache_pkt.end()) {
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return nullptr;
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}
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return &it->second;
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}
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uint32_t NackList::getCacheMS() {
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while (_nack_cache_seq.size() > 2) {
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auto back_stamp = getRtpStamp(_nack_cache_seq.back());
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if (back_stamp == -1) {
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_nack_cache_seq.pop_back();
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continue;
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}
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auto front_stamp = getRtpStamp(_nack_cache_seq.front());
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if (front_stamp == -1) {
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_nack_cache_seq.pop_front();
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continue;
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}
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if (back_stamp >= front_stamp) {
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return back_stamp - front_stamp;
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}
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// 很有可能回环了
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return back_stamp + (UINT32_MAX - front_stamp);
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}
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return 0;
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}
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int64_t NackList::getRtpStamp(uint16_t seq) {
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auto it = _nack_cache_pkt.find(seq);
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if (it == _nack_cache_pkt.end()) {
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return -1;
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}
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return it->second->getStampMS(false);
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}
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////////////////////////////////////////////////////////////////////////////////////////////////
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NackContext::NackContext() {
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setOnNack(nullptr);
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}
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void NackContext::received(uint16_t seq, bool is_rtx) {
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if (!_started) {
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// 记录第一个seq
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_started = true;
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_nack_seq = seq - 1;
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}
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if (seq < _nack_seq && _nack_seq != UINT16_MAX && seq < 1024 && _nack_seq > UINT16_MAX - 1024) {
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// seq回环,清空回环前状态
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makeNack(UINT16_MAX, true);
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_seq.emplace(seq);
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return;
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}
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if (is_rtx || (seq < _nack_seq && _nack_seq != UINT16_MAX)) {
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// seq非回环回退包，猜测其为重传包，清空其nack状态
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clearNackStatus(seq);
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return;
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}
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auto pr = _seq.emplace(seq);
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if (!pr.second) {
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// seq重复, 忽略
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return;
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}
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auto max_seq = *_seq.rbegin();
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auto min_seq = *_seq.begin();
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auto diff = max_seq - min_seq;
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if (diff > (UINT16_MAX >> 1)) {
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// 回环后，收到回环前的大值seq, 忽略掉
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_seq.erase(max_seq);
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return;
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}
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if (min_seq == (uint16_t)(_nack_seq + 1) && _seq.size() == (size_t)diff + 1) {
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// 都是连续的seq，未丢包
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_seq.clear();
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_nack_seq = max_seq;
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} else {
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// seq不连续，有丢包
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makeNack(max_seq, false);
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}
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}
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void NackContext::makeNack(uint16_t max_seq, bool flush) {
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// 尝试移除前面部分连续的seq
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eraseFrontSeq();
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// 最多生成5个nack包，防止seq大幅跳跃导致一直循环
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auto max_nack = 5u;
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while (_nack_seq != max_seq && max_nack--) {
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// 一次不能发送超过16+1个rtp的状态
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uint16_t nack_rtp_count = std::min<uint16_t>(FCI_NACK::kBitSize, max_seq - (uint16_t)(_nack_seq + 1));
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if (!flush && nack_rtp_count < kNackRtpSize) {
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// 非flush状态下，seq个数不足以发送一次nack
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break;
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}
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vector<bool> vec;
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vec.resize(nack_rtp_count, false);
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for (size_t i = 0; i < nack_rtp_count; ++i) {
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vec[i] = _seq.find((uint16_t)(_nack_seq + i + 2)) == _seq.end();
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}
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doNack(FCI_NACK(_nack_seq + 1, vec), true);
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_nack_seq += nack_rtp_count + 1;
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// 返回第一个比_last_max_seq大的元素
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auto it = _seq.upper_bound(_nack_seq);
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// 移除 <=_last_max_seq 的seq
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_seq.erase(_seq.begin(), it);
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}
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}
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void NackContext::setOnNack(onNack cb) {
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if (cb) {
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_cb = std::move(cb);
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} else {
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_cb = [](const FCI_NACK &nack) {};
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}
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}
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void NackContext::doNack(const FCI_NACK &nack, bool record_nack) {
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if (record_nack) {
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recordNack(nack);
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}
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_cb(nack);
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}
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void NackContext::eraseFrontSeq() {
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// 前面部分seq是连续的，未丢包，移除之
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for (auto it = _seq.begin(); it != _seq.end();) {
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if (*it != (uint16_t)(_nack_seq + 1)) {
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// seq不连续，丢包了
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break;
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}
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_nack_seq = *it;
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it = _seq.erase(it);
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}
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}
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void NackContext::clearNackStatus(uint16_t seq) {
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auto it = _nack_send_status.find(seq);
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if (it == _nack_send_status.end()) {
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return;
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}
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//收到重传包与第一个nack包间的时间约等于rtt时间
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auto rtt = getCurrentMillisecond() - it->second.first_stamp;
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_nack_send_status.erase(it);
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// 限定rtt在合理有效范围内
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_rtt = max<int>(10, min<int>(rtt, kNackMaxMS / kNackMaxCount));
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}
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void NackContext::recordNack(const FCI_NACK &nack) {
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auto now = getCurrentMillisecond();
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auto i = nack.getPid();
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for (auto flag : nack.getBitArray()) {
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if (flag) {
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auto &ref = _nack_send_status[i];
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ref.first_stamp = now;
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ref.update_stamp = now;
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ref.nack_count = 1;
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}
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++i;
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}
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// 记录太多了，移除一部分早期的记录
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while (_nack_send_status.size() > kNackMaxSize) {
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_nack_send_status.erase(_nack_send_status.begin());
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}
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}
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uint64_t NackContext::reSendNack() {
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set<uint16_t> nack_rtp;
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auto now = getCurrentMillisecond();
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for (auto it = _nack_send_status.begin(); it != _nack_send_status.end();) {
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if (now - it->second.first_stamp > kNackMaxMS) {
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// 该rtp丢失太久了，不再要求重传
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it = _nack_send_status.erase(it);
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continue;
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}
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if (now - it->second.update_stamp < kNackIntervalRatio * _rtt) {
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// 距离上次nack不足2倍的rtt，不用再发送nack
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++it;
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continue;
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}
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// 此rtp需要请求重传
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nack_rtp.emplace(it->first);
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// 更新nack发送时间戳
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it->second.update_stamp = now;
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if (++(it->second.nack_count) == kNackMaxCount) {
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// nack次数太多，移除之
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it = _nack_send_status.erase(it);
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continue;
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}
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++it;
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}
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int pid = -1;
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vector<bool> vec;
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for (auto it = nack_rtp.begin(); it != nack_rtp.end();) {
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if (pid == -1) {
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pid = *it;
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vec.assign(FCI_NACK::kBitSize, false);
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++it;
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continue;
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}
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auto inc = *it - pid;
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if (inc > (ssize_t)FCI_NACK::kBitSize) {
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// 新的nack包
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doNack(FCI_NACK(pid, vec), false);
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pid = -1;
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continue;
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}
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// 这个包丢了
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vec[inc - 1] = true;
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++it;
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}
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if (pid != -1) {
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doNack(FCI_NACK(pid, vec), false);
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}
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// 没有任何包需要重传时返回0，否则返回下次重传间隔(不得低于5ms)
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return _nack_send_status.empty() ? 0 : _rtt;
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}
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} // namespace mediakit
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