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

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     #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 || bytesToWrite == 0 || bytesToRead == 0)
             scheduleTransfer();
     }