libreoffice-online/common/MessageQueue.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_MESSAGEQUEUE_HPP
#define INCLUDED_MESSAGEQUEUE_HPP

#include <algorithm>
#include <condition_variable>
#include <functional>
#include <map>
#include <mutex>
#include <vector>

/// Thread-safe message queue (FIFO).
template <typename T>
class MessageQueueBase
{
public:
    typedef T Payload;

    MessageQueueBase()
    {
    }

    virtual ~MessageQueueBase()
    {
        clear();
    }

    MessageQueueBase(const MessageQueueBase&) = delete;
    MessageQueueBase& operator=(const MessageQueueBase&) = delete;

    /// Thread safe insert the message.
    void put(const Payload& value)
    {
        if (value.empty())
        {
            throw std::runtime_error("Cannot queue empty item.");
        }

        std::unique_lock<std::mutex> lock(_mutex);
        put_impl(value);
        lock.unlock();
        _cv.notify_one();
    }

    void put(const std::string& value)
    {
        put(Payload(value.data(), value.data() + value.size()));
    }

    /// Thread safe obtaining of the message.
    /// timeoutMs can be 0 to signify infinity.
    /// Returns an empty payload on timeout.
    Payload get(const unsigned timeoutMs = 0)
    {
        std::unique_lock<std::mutex> lock(_mutex);

        if (timeoutMs > 0)
        {
            if (!_cv.wait_for(lock, std::chrono::milliseconds(timeoutMs),
                              [this] { return wait_impl(); }))
            {
                return Payload();
            }
        }
        else
        {
            _cv.wait(lock, [this] { return wait_impl(); });
        }

        return get_impl();
    }

    /// Thread safe removal of all the pending messages.
    void clear()
    {
        std::unique_lock<std::mutex> lock(_mutex);
        clear_impl();
    }

    /// Thread safe remove_if.
    void remove_if(const std::function<bool(const Payload&)>& pred)
    {
        std::unique_lock<std::mutex> lock(_mutex);
        std::remove_if(_queue.begin(), _queue.end(), pred);
    }

protected:
    virtual void put_impl(const Payload& value)
    {
        const auto msg = std::string(value.data(), value.size());
        _queue.push_back(value);
    }

    bool wait_impl() const
    {
        return _queue.size() > 0;
    }

    virtual Payload get_impl()
    {
        Payload result = _queue.front();
        _queue.erase(_queue.begin());
        return result;
    }

    void clear_impl()
    {
        _queue.clear();
    }

    /// Get the queue lock when accessing members of derived classes.
    std::unique_lock<std::mutex> getLock() { return std::unique_lock<std::mutex>(_mutex); }

protected:
    std::vector<Payload> _queue;

private:
    mutable std::mutex _mutex;
    std::condition_variable _cv;

};

typedef MessageQueueBase<std::vector<char>> MessageQueue;

/// MessageQueue specialized for priority handling of tiles.
class TileQueue : public MessageQueue
{
    friend class TileQueueTests;

private:
    class CursorPosition
    {
    public:
        int Part;
        int X;
        int Y;
        int Width;
        int Height;
    };

public:

    TileQueue() :
        _lastTileGetTime(std::chrono::steady_clock::now()),
        _lastGetTime(_lastTileGetTime),
        _lastGetTile(true)
    {
    }

    void updateCursorPosition(int viewId, int part, int x, int y, int width, int height)
    {
        const auto cursorPosition = CursorPosition({ part, x, y, width, height });

        auto lock = getLock();

        auto it = _cursorPositions.lower_bound(viewId);
        if (it != _cursorPositions.end() && it->first == viewId)
        {
            it->second = cursorPosition;
        }
        else
        {
            _cursorPositions.insert(it, std::make_pair(viewId, cursorPosition));
        }

        // Move to front, so the current front view
        // becomes the second.
        const auto view = std::find(_viewOrder.begin(), _viewOrder.end(), viewId);
        if (view != _viewOrder.end())
        {
            _viewOrder.erase(view);
        }

        _viewOrder.push_back(viewId);
    }

    void removeCursorPosition(int viewId)
    {
        auto lock = getLock();

        const auto view = std::find(_viewOrder.begin(), _viewOrder.end(), viewId);
        if (view != _viewOrder.end())
        {
            _viewOrder.erase(view);
        }

        _cursorPositions.erase(viewId);
    }

protected:
    virtual void put_impl(const Payload& value) override;

    virtual Payload get_impl() override;

private:
    /// Search the queue for a duplicate tile and remove it (if present).
    void removeTileDuplicate(const std::string& tileMsg);

    /// Search the queue for a duplicate callback and remove it (if present).
    ///
    /// This removes also callbacks that are made invalid by the current
    /// message, like the new cursor position invalidates the old one etc.
    void removeCallbackDuplicate(const std::string& callbackMsg);

    /// Find the index of the first non-preview entry.
    /// When preferTiles is false, it'll return index of
    /// the first non-tile, otherwise, the index of the
    /// first tile is returned.
    /// Returns -1 if only previews are left.
    int findFirstNonPreview(bool preferTiles) const;

    /// Returns true if we should try to return
    /// a tile, otherwise a non-tile.
    bool shouldPreferTiles() const;

    /// Update the tile/non-tile timestamps to
    /// track how much time we spend for each.
    /// isTile marks if the current message
    /// is a tile or not.
    void updateTimestamps(const bool isTile);

    /// Given a positive index, move it to the top.
    void bumpToTop(const size_t index);

    /// Priority of the given tile message.
    /// -1 means the lowest prio (the tile does not intersect any of the cursors),
    /// the higher the number, the bigger is priority [up to _viewOrder.size()-1].
    int priority(const std::string& tileMsg);

private:
    std::map<int, CursorPosition> _cursorPositions;

    /// Check the views in the order of how the editing (cursor movement) has
    /// been happening (0 == oldest, size() - 1 == newest).
    std::vector<int> _viewOrder;

    std::chrono::steady_clock::time_point _lastTileGetTime;
    std::chrono::steady_clock::time_point _lastGetTime;
    bool _lastGetTile;

    /// For responsiveness, we shouldn't have higher latency.
    static const int MaxTileSkipDurationMs = 100;
};

#endif

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