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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();
 }


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Qt 4.6.3