////  PacketQueue.cpp//  libraries/networking/src/udt////  Created by Clement on 9/16/15.//  Copyright 2015 High Fidelity, Inc.////  Distributed under the Apache License, Version 2.0.//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html// #include "PacketQueue.h" #include "PacketList.h" using namespace udt; PacketQueue::PacketQueue(MessageNumber messageNumber) : _currentMessageNumber(messageNumber) {    _channels.emplace_front(new std::list<PacketPointer>());    _currentChannel = _channels.begin();} MessageNumber PacketQueue::getNextMessageNumber() {    static const MessageNumber MAX_MESSAGE_NUMBER = MessageNumber(1) << MESSAGE_NUMBER_SIZE;    _currentMessageNumber = (_currentMessageNumber + 1) % MAX_MESSAGE_NUMBER;    return _currentMessageNumber;} bool PacketQueue::isEmpty() const {    LockGuard locker(_packetsLock);     // Only the main channel and it is empty    return _channels.size() == 1 && _channels.front()->empty();} PacketQueue::PacketPointer PacketQueue::takePacket() {    LockGuard locker(_packetsLock);     if (isEmpty()) {        return PacketPointer();    }     // handle the case where we are looking at the first channel and it is empty    if (_currentChannel == _channels.begin() && (*_currentChannel)->empty()) {        ++_currentChannel;    }     // at this point the current channel should always not be at the end and should also not be empty    Q_ASSERT(_currentChannel != _channels.end());     auto& channel = *_currentChannel;     Q_ASSERT(!channel->empty());     // Take front packet    auto packet = std::move(channel->front());    channel->pop_front();     // Remove now empty channel (Don't remove the main channel)    if (channel->empty() && _currentChannel != _channels.begin()) {        // erase the current channel and slide the iterator to the next channel        _currentChannel = _channels.erase(_currentChannel);    } else {        ++_currentChannel;    }     // push forward our number of channels taken from    ++_channelsVisitedCount;     // check if we need to restart back at the front channel (main)    // to respect our capped number of channels considered concurrently    static const int MAX_CHANNELS_SENT_CONCURRENTLY = 16;     if (_currentChannel == _channels.end() || _channelsVisitedCount >= MAX_CHANNELS_SENT_CONCURRENTLY) {        _channelsVisitedCount = 0;        _currentChannel = _channels.begin();    }     return packet;} void PacketQueue::queuePacket(PacketPointer packet) {    LockGuard locker(_packetsLock);    _channels.front()->push_back(std::move(packet));} void PacketQueue::queuePacketList(PacketListPointer packetList) {    if (packetList->isOrdered()) {        packetList->preparePackets(getNextMessageNumber());    }     LockGuard locker(_packetsLock);    _channels.emplace_back(new std::list<PacketPointer>());    _channels.back()->swap(packetList->_packets);}