Qt C++ how to correctly delete QFutureWatcher? - qt

Question

My code sometimes crashes due to future's async.
This is not production code, just very simple stuff for demonstrating what i want to do.
I have to download some info and then return first obtained result. Just imagine i do not want to wait so i'm using QFutureWatcher too speed up the downloading.
When i obtained the result (first or second instance) i want to return the result IMMEDIATELY (i mean i do not want to use QFutureWatcher::waitForFinished.
(If i received finished signal from first instance, i no longer need the second one. Or the same for the first.
In production code function download i cannot access to QNetworkReply, so the pending request could not be aborted.
Sometimes this code crashes. What am i doing wrong?
#include <QFutureWatcher>
#include <QtConcurrent>
#include <QEventLoop>
#include <QTimer>
#include <QNetworkReply>
#include <QNetworkRequest>
#include <QNetworkAccessManager>
QByteArray download(const QUrl &url)
{
QNetworkAccessManager manager;
QNetworkRequest req(url);
req.setAttribute(QNetworkRequest::SynchronousRequestAttribute, true);
QNetworkReply *reply = manager.get(req);
reply->deleteLater();
return reply->readAll();
}
QByteArray downloadSmth(const QUrl &urlFirst, const QUrl &urlSecond)
{
typedef QFutureWatcher<QByteArray> FutureWatcher;
FutureWatcher *first = new FutureWatcher;
FutureWatcher *second = new FutureWatcher;
QByteArray res;
QEventLoop loop;
QObject::connect(first, &FutureWatcher::finished, [&res, &loop, first] {
res = first->result();
loop.quit();
});
QObject::connect(second, &FutureWatcher::finished, [&res, &loop, second] {
res = second->result();
loop.quit();
});
QTimer timer;
timer.setSingleShot(true);
QObject::connect(&timer, &QTimer::timeout, &loop, &QEventLoop::quit);
first->setFuture(
QtConcurrent::run([&urlFirst] {
return download(urlFirst);
}));
second->setFuture(
QtConcurrent::run([&urlSecond] {
return download(urlSecond);
}));
timer.start(60 * 1000);
loop.exec();
if (timer.isActive()) {
timer.stop();
}
first->deleteLater();
second->deleteLater();
return res;
}