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for(int i=0; i<100; ++i)
 auto res = std::async(std::launch::async, std::bind(std::function<int (worker &, int)>(&worker::get), w, 2));

Storage storage;
QImage *img[100];
int error[100]; //  опционально, код ошибки операции, если операция выполняется указатель пустой

for (int i=0; i<100; ++i) storage.load(QString("%1.jpg").arg(i), &img[i], *error[i]);

...

while(1)
   for(int i=0; i<100; ++i)
      if(img[i] && !err[i])
           painter.draw(0,0,img[i]);

...

Чтение картинки в отдельном потоке это обычный
QImage *tmp = new QImage(fileName);
img = tmp;

#include "cachedisk.h"

#include <QTabWidget>

CacheDisk::CacheDisk()
{
//    connect(this, SIGNAL(Finish()), this, SLOT(Finished()), Qt::QueuedConnection);
    worked = false;
}

void CacheDisk::Read(QString fileName, QPixmap **pix)
{
    taskList.append(QPair<QString, QPixmap**>(fileName,pix));

    if(!worked) {
        worked = true;
        QPair<QString, QPixmap**> param = taskList.takeFirst();

        pixSave = param.second;

        future = QtConcurrent::run(this, &CacheDisk::ReadInThread, param.first, param.second);
        futureWather.setFuture(future);
        connect(&futureWather, SIGNAL(finished()), this, SLOT(Finished()));
//        ReadInThread(param.first, param.second);
    }
}

void CacheDisk::Finished()
{
    *pixSave = future.result();
    qDebug()<<"finish"<<*pixSave;


    QLabel *l = new QLabel;
    l->setPixmap(**pixSave);
    l->show();

    worked = false;

    if(!taskList.empty()) {
        worked = true;
        QPair<QString, QPixmap**> param = taskList.takeFirst();
        QtConcurrent::run(this, &CacheDisk::ReadInThread, param.first, param.second);
    }
}

QPixmap* CacheDisk::ReadInThread(QString fileName, QPixmap **pix)
{
    QPixmap *tmpPixmap = new QPixmap(fileName);
qDebug()<<tmpPixmap;

    return tmpPixmap;
}

#ifndef CACHEDISK_H
#define CACHEDISK_H

#include <QObject>
#include <QtConcurrentRun>
#include <QImage>
#include <QPixmap>
#include <QLabel>
#include <QFutureWatcher>

class CacheDisk: public QObject
{
    Q_OBJECT
    QPixmap **pixSave;
    QList<QPair<QString,QPixmap**> > taskList;

    QPixmap *ReadInThread(QString fileName, QPixmap **pix);
    bool worked;

    QFuture<QPixmap*> future;
    QFutureWatcher<QPixmap*> futureWather;

private slots:
    void Finished();

public:
    CacheDisk();
    void Read(QString fileName, QPixmap **pix);
};

#endif // CACHEDISK_H

#include <QApplication>
#include <QPixmapCache>
//#include "zzz.h"
//#include "diskcache.h"
#include "cachedisk.h"
#include <QtGui>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    CacheDisk cacheDisk;
    QPixmap *pix = 0;
    cacheDisk.Read("D:/WORK/learn/1.jpg", &pix);

    return app.exec();
}