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# ratecontroller.cpp Example File
network/torrent/ratecontroller.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2004-2006 Trolltech ASA. All rights reserved.
    **
    ** This file is part of the example classes of the Qt Toolkit.
    **
    ** Licensees holding valid Qt Preview licenses may use this file in
    ** accordance with the Qt Preview License Agreement provided with the
    ** Software.
    **
    ** See http://www.trolltech.com/pricing.html or email sales@trolltech.com for
    ** information about Qt Commercial License Agreements.
    **
    ** Contact info@trolltech.com if any conditions of this licensing are
    ** not clear to you.
    **
    ** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
    ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
    **
    ****************************************************************************/

    #include "peerwireclient.h"
    #include "ratecontroller.h"

    #include <QtCore>

    Q_GLOBAL_STATIC(RateController, rateController)

    RateController *RateController::instance()
    {
        return rateController();
    }

    void RateController::addSocket(PeerWireClient *socket)
    {
        connect(socket, SIGNAL(readyToTransfer()), this, SLOT(scheduleTransfer()));
        socket->setReadBufferSize(downLimit * 4);
        sockets << socket;
        scheduleTransfer();
    }

    void RateController::removeSocket(PeerWireClient *socket)
    {
        disconnect(socket, SIGNAL(readyToTransfer()), this, SLOT(scheduleTransfer()));
        socket->setReadBufferSize(0);
        sockets.remove(socket);
    }

    void RateController::setDownloadLimit(int bytesPerSecond)
    {
        downLimit = bytesPerSecond;
        foreach (PeerWireClient *socket, sockets)
            socket->setReadBufferSize(downLimit * 4);
    }

    void RateController::scheduleTransfer()
    {
        if (transferScheduled)
            return;
        transferScheduled = true;
        QTimer::singleShot(50, this, SLOT(transfer()));
    }

    void RateController::transfer()
    {
        transferScheduled = false;
        if (sockets.isEmpty())
            return;

        int msecs = 1000;
        if (!stopWatch.isNull())
            msecs = qMin(msecs, stopWatch.elapsed());

        qint64 bytesToWrite = (upLimit * msecs) / 1000;
        qint64 bytesToRead = (downLimit * msecs) / 1000;
        if (bytesToWrite == 0 && bytesToRead == 0) {
            scheduleTransfer();
            return;
        }

        QSet<PeerWireClient *> pendingSockets;
        foreach (PeerWireClient *client, sockets) {
            if (client->canTransferMore())
                pendingSockets << client;
        }
        if (pendingSockets.isEmpty())
            return;

        stopWatch.start();

        bool canTransferMore;
        do {
            canTransferMore = false;
            qint64 writeChunk = qMax<qint64>(1, bytesToWrite / pendingSockets.size());
            qint64 readChunk = qMax<qint64>(1, bytesToRead / pendingSockets.size());

            QSetIterator<PeerWireClient *> it(pendingSockets);
            while (it.hasNext() && (bytesToWrite > 0 || bytesToRead > 0)) {
                PeerWireClient *socket = it.next();
                if (socket->state() != QAbstractSocket::ConnectedState) {
                    pendingSockets.remove(socket);
                    continue;
                }

                bool dataTransferred = false;
                qint64 available = qMin<qint64>(socket->socketBytesAvailable(), readChunk);
                if (available > 0) {
                    qint64 readBytes = socket->readFromSocket(qMin<qint64>(available, bytesToRead));
                    if (readBytes > 0) {
                        bytesToRead -= readBytes;
                        dataTransferred = true;
                    }
                }

                if (upLimit * 2 > socket->bytesToWrite()) {
                    qint64 chunkSize = qMin<qint64>(writeChunk, bytesToWrite);
                    qint64 toWrite = qMin(upLimit * 2 - socket->bytesToWrite(), chunkSize);
                    if (toWrite > 0) {
                        qint64 writtenBytes = socket->writeToSocket(toWrite);
                        if (writtenBytes > 0) {
                            bytesToWrite -= writtenBytes;
                            dataTransferred = true;
                        }
                    }
                }

                if (dataTransferred && socket->canTransferMore())
                    canTransferMore = true;
                else
                    pendingSockets.remove(socket);
            }
        } while (canTransferMore && (bytesToWrite > 0 || bytesToRead > 0) && !pendingSockets.isEmpty());

        if (canTransferMore)
            scheduleTransfer();
    }