Concurrent file downloading

[Alir3z4]

Download one file at the time with source code below is easy, and also download multiply file also isn't problem when using http://doc.qt.io/qt-4.8/QQueue, but downloading files in parallel i can't get it!
Assume we have:
I make code shorter and remove other codes for demonstration purpose ;)
downloader.h

#ifndef DOWNLOADER_H
#define DOWNLOADER_H
 
#include <QObject>
#include <QFile>
#include <QFileInfo>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QUrl>
 
class Dowloader : public QObject
{
    Q_OBJECT
public:
    explicit Dowloader(QObject *parent = 0);
 
public slots:
    void theDownload(const QString &urlLink);
 
private slots:
    void startRequest(const QUrl &url);
    void httpReadyRead();
    void httpFinished();
 
private:
    QNetworkAccessManager manager;
    QNetworkReply *reply;
    QFile *file;
};
 
#endif // DOWNLOADER_H

#ifndef DOWNLOADER_H
#define DOWNLOADER_H

#include <QObject>
#include <QFile>
#include <QFileInfo>
#include <QNetworkAccessManager>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QUrl>

class Dowloader : public QObject
{
    Q_OBJECT
public:
    explicit Dowloader(QObject *parent = 0);

public slots:
    void theDownload(const QString &urlLink);

private slots:
    void startRequest(const QUrl &url);
    void httpReadyRead();
    void httpFinished();

private:
    QNetworkAccessManager manager;
    QNetworkReply *reply;
    QFile *file;
};

#endif // DOWNLOADER_H

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downloader.cpp

#include "dowloader.h"
 
Dowloader::Dowloader(QObject *parent) :
    QObject(parent)
{}
 
void Dowloader::theDownload(const QString &urlLink)
{
    QUrl url(urlLink);
    QFileInfo fInfo(url.path());
    QString fileName = fInfo.fileName();
    if(fileName.isEmpty())
        fileName  = "download";
 
    file = new QFile(fileName);
 
    if(!file->open(QIODevice::WriteOnly)){
        delete file;
        file = 0;
        return;
    }
    startRequest(url);
}
 
void Dowloader::replyMetaDataChanged()
{}
 
void Dowloader::startRequest(const QUrl &url)
{
    QNetworkRequest request(url);
    reply = manager.get(request);
    // conncet signals
    connect(reply, SIGNAL(metaDataChanged()), this, SLOT(replyMetaDataChanged()));
    connect(reply, SIGNAL(readyRead()), this, SLOT(httpReadyRead()));
    connect(reply, SIGNAL(finished()), this, SLOT(httpFinished()));
}
 
void Dowloader::httpReadyRead()
{
    if(file)	file->write(reply->readAll());
}
 
void Dowloader::httpFinished()
{
    file->flush();
    file->close();
    reply->deleteLater();
    reply = 0;
    delete file;
    file = 0;
}

#include "dowloader.h"

Dowloader::Dowloader(QObject *parent) :
    QObject(parent)
{}

void Dowloader::theDownload(const QString &urlLink)
{
    QUrl url(urlLink);
    QFileInfo fInfo(url.path());
    QString fileName = fInfo.fileName();
    if(fileName.isEmpty())
        fileName  = "download";

    file = new QFile(fileName);

    if(!file->open(QIODevice::WriteOnly)){
        delete file;
        file = 0;
        return;
    }
    startRequest(url);
}

void Dowloader::replyMetaDataChanged()
{}

void Dowloader::startRequest(const QUrl &url)
{
    QNetworkRequest request(url);
    reply = manager.get(request);
    // conncet signals
    connect(reply, SIGNAL(metaDataChanged()), this, SLOT(replyMetaDataChanged()));
    connect(reply, SIGNAL(readyRead()), this, SLOT(httpReadyRead()));
    connect(reply, SIGNAL(finished()), this, SLOT(httpFinished()));
}

void Dowloader::httpReadyRead()
{
    if(file)	file->write(reply->readAll());
}

void Dowloader::httpFinished()
{
    file->flush();
    file->close();
    reply->deleteLater();
    reply = 0;
    delete file;
    file = 0;
}

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The main problem here is, in the httpReadyRead() ans httpFinished() how can operate on the correct file, reply? as you see in the *.h file they are *pointer, it means when i add new file current QNetworkReply *reply, QFile *file, gonna re-initialize with new values!
What changes need in this code to make Concurrent file downloading possible? // Doesn't mean provide some code or something, just give me a scenario about it!

Thanks

[Lykurg]

QSignalMapper and QHash can help.

[Alir3z4]

QSignalMapper and QHash can help.

Yes, first thing came to my head was using QHash, QSignalMapper, but what should i keep in the QHash?
pointer or reference?
pointer like this?

QHash<QUrl, QHash<QNetworkReply*, QFile*> > *downloads;

QHash<QUrl, QHash<QNetworkReply*, QFile*> > *downloads;

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if pointers, what happen when i add new download and re-initialize *reply*, *file, or something like that? // or maybe i shouldn't use *reply*, *file and just make pointers add them to hash on the fly?
or i have to keep ref in it?

[Lykurg]

Pointers and file/replay aren't getting overwritten since you store it in the hash. Use QHash<QNetworkReply*, QFile*>. Just make sure you delete the pointers after the downloads are finished.

[ChrisW67]

You can also not store the reply pointer at all and use the QNetworkAccessManager::finished() signal, which passes the QNetworkReply object that finished. This is really only suitable for smaller files where the entire content is easily stored in memory and progress indication is not important.