libreoffice-online/wsd/SenderQueue.hpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

#ifndef INCLUDED_SENDERQUEUE_HPP
#define INCLUDED_SENDERQUEUE_HPP

#include <condition_variable>
#include <deque>
#include <memory>
#include <mutex>
#include <vector>

#include <Poco/Dynamic/Var.h>
#include <Poco/JSON/JSON.h>
#include <Poco/JSON/Object.h>
#include <Poco/JSON/Parser.h>

#include "common/SigUtil.hpp"
#include "LOOLWebSocket.hpp"
#include "Log.hpp"
#include "TileDesc.hpp"

struct SendItem
{
    std::weak_ptr<LOOLWebSocket> Socket;
    std::shared_ptr<Message> Data;
    std::string Meta;
    std::chrono::steady_clock::time_point BirthTime;
};

/// A queue of data to send to certain Session's WS.
template <typename Item>
class SenderQueue final
{
public:

    SenderQueue() :
        _stop(false)
    {
    }

    bool stopping() const { return _stop || TerminationFlag; }
    void stop()
    {
        _stop = true;
        _cv.notify_all();
    }

    size_t enqueue(const Item& item)
    {
        std::unique_lock<std::mutex> lock(_mutex);
        if (!stopping())
        {
            if (deduplicate(item))
            {
                _queue.push_back(item);
            }
        }

        const size_t queuesize = _queue.size();
        lock.unlock();

        _cv.notify_one();
        return queuesize;
    }

    bool waitDequeue(Item& item,
                     const size_t timeoutMs = std::numeric_limits<size_t>::max())
    {
        const auto timeToWait = std::chrono::milliseconds(timeoutMs);

        std::unique_lock<std::mutex> lock(_mutex);

        if (!_queue.empty() ||
            _cv.wait_for(lock, timeToWait, [this](){ return !_queue.empty() || stopping(); }))
        {
            if (!stopping())
            {
                item = _queue.front();
                _queue.pop_front();
                return true;
            }

            LOG_DBG("SenderQueue: stopping");
            return false;
        }

        return false;
    }

    size_t size() const
    {
        std::lock_guard<std::mutex> lock(_mutex);
        return _queue.size();
    }

private:
    /// Deduplicate messages based on the new one.
    /// Returns true if the new message should be
    /// enqueued, otherwise false.
    bool deduplicate(const Item& item)
    {
        // Deduplicate messages based on the incoming one.
        const std::string command = item->firstToken();
        if (command == "tile:")
        {
            // Remove previous identical tile, if any, and use most recent (incoming).
            const TileDesc newTile = TileDesc::parse(item->firstLine());
            const auto& pos = std::find_if(_queue.begin(), _queue.end(),
                [&newTile](const queue_item_t& cur)
                {
                    return (cur->firstToken() == "tile:" &&
                            newTile == TileDesc::parse(cur->firstLine()));
                });

            if (pos != _queue.end())
            {
                _queue.erase(pos);
            }
        }
        else if (command == "statusindicatorsetvalue:" ||
                 command == "invalidatecursor:")
        {
            // Remove previous identical enties of this command,
            // if any, and use most recent (incoming).
            const auto& pos = std::find_if(_queue.begin(), _queue.end(),
                [&command](const queue_item_t& cur)
                {
                    return (cur->firstToken() == command);
                });

            if (pos != _queue.end())
            {
                _queue.erase(pos);
            }
        }
        else if (command == "invalidateviewcursor:")
        {
            // Remove previous cursor invalidation for same view,
            // if any, and use most recent (incoming).
            const std::string newMsg = item->jsonString();
            Poco::JSON::Parser newParser;
            const auto newResult = newParser.parse(newMsg);
            const auto& newJson = newResult.extract<Poco::JSON::Object::Ptr>();
            const auto viewId = newJson->get("viewId").toString();
            const auto& pos = std::find_if(_queue.begin(), _queue.end(),
                [command, viewId](const queue_item_t& cur)
                {
                    if (cur->firstToken() == command)
                    {
                        const std::string msg = cur->jsonString();
                        Poco::JSON::Parser parser;
                        const auto result = parser.parse(msg);
                        const auto& json = result.extract<Poco::JSON::Object::Ptr>();
                        return (viewId == json->get("viewId").toString());
                    }

                    return false;
                });

            if (pos != _queue.end())
            {
                _queue.erase(pos);
            }
        }

        return true;
    }

private:
    mutable std::mutex _mutex;
    std::condition_variable _cv;
    std::deque<Item> _queue;
    typedef typename std::deque<Item>::value_type queue_item_t;
    std::atomic<bool> _stop;
};

/// Pool of sender threads.
/// These are dedicated threads that only dequeue from
/// the SenderQueue and send to the target Session's WS.
/// This pool has long-running threads that grow
/// only on congention and shrink otherwise.
class SenderThreadPool final
{
public:
    SenderThreadPool() :
        _optimalThreadCount(std::min(2U, std::thread::hardware_concurrency())),
        _maxThreadCount(_optimalThreadCount),
        _idleThreadCount(0),
        _stop(false)
    {
        LOG_INF("Creating SenderThreadPool with " << _optimalThreadCount << " optimal threads.");
        for (size_t i = 0; i < _optimalThreadCount; ++i)
        {
            _threads.push_back(createThread());
        }
    }

    ~SenderThreadPool()
    {
        // Stop us and the queue.
        stop();
        //SenderQueue::instance().stop();

        for (const auto& threadData : _threads)
        {
            if (threadData && threadData->joinable())
            {
                threadData->join();
            }
        }
    }

    void stop() { _stop = true; }
    bool stopping() const { return _stop || TerminationFlag; }

    void incMaxThreadCount() { ++_maxThreadCount; }
    void decMaxThreadCount() { --_maxThreadCount; }

private:

    /// Count idle threads safely.
    /// Decrements count on ctor, and increments on dtor.
    class IdleCountGuard final
    {
    public:
        IdleCountGuard(std::atomic<size_t>& var) :
            _var(var)
        {
            --_var;
        }

        ~IdleCountGuard()
        {
            ++_var;
        }

    private:
        std::atomic<size_t>& _var;
    };

    typedef std::thread ThreadData;

    /// Dequeue a SendItem and send it.
    bool dispatchItem(const size_t timeoutMs);

    /// Create a new thread and add to the pool.
    std::shared_ptr<ThreadData> createThread();

    /// Rebalance the number of threads.
    /// Returns true if we need to reduce the threads.
    bool rebalance();

    /// Grow the pool if congestion is detected.
    void checkAndGrow();

    /// The worker thread entry function.
    void threadFunction(const std::shared_ptr<ThreadData>& data);

private:
    /// A minimum of 2, but ideally as many as cores.
    const size_t _optimalThreadCount;

    /// Never exceed this number of threads.
    size_t _maxThreadCount;

    /// The number of threads not sending data.
    std::atomic<size_t> _idleThreadCount;

    /// Stop condition to take the pool down.
    std::atomic<bool> _stop;

    std::vector<std::shared_ptr<ThreadData>> _threads;
    mutable std::mutex _mutex;

    /// How often to do housekeeping when we idle.
    static constexpr size_t HousekeepIdleIntervalMs = 60000;
};

#endif

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