Thread sending http request using Qt - c++

Question

I am trying to create a thread (HttpWorker) that when required wakes up and sends a http request. I would like this to be done in a single thread. I am using Qt for the implementation.
The way I thought i would do it is to have a class MyHttpWorker, move it to another thread, connect the slots/signals etc. Then on thread start I would use QNetworkAccessManager to call get requests. I would use QWaitCondition to pause the thread after the request has been sent and I would resume this thread whenever I need to send another one.
However, when I pause the httpworker thread, the FinishedSlot is not called at all. If I use the class to simply call one http request, it executes with no problem. So the problem is connected to QWaitCondition (or just freezing the threads in general).
I could simply create and destroy one worker and thread for each request I have, but I require to send lot of http requests, so I think this method would be way too consuming (creating threads and destroying them over and over).
I appreciate any help I can get.
Here is my code:
MyHttpWorker.h
#include <QNetworkReply>
#include <QDebug>
#include <QObject>
#include <QNetworkAccessManager>
#include <QThread>
#include <QWaitCondition>
#include <QMutex>
class MyHttpWorker : public QObject
{
Q_OBJECT
QNetworkAccessManager* nam;
QMutex syncPause;
QWaitCondition pauseCond;
public:
explicit MyHttpWorker(QObject *parent = 0);
void MyWake();
public slots:
void SetTheThread(QThread* thread);
void MyStart();
void finishedSlot(QNetworkReply* reply);
};
MyHttpWorker.cpp
MyHttpWorker::MyHttpWorker(QObject *parent) :
QObject(parent)
{
nam = new QNetworkAccessManager(this);
QObject::connect(nam, SIGNAL(finished(QNetworkReply*)), this, SLOT(finishedSlot(QNetworkReply*)));
}
void MyHttpWorker::finishedSlot(QNetworkReply* reply)
{
qDebug() << "Finished"; //This slot is never even reached, when i used QWaitCond...
if (reply->error() == QNetworkReply::NoError)
{
QByteArray bytes = reply->readAll();
QString string(bytes);
qDebug() << string;
}else
{
qDebug() << reply->errorString();
}
reply->deleteLater();
}
void MyHttpWorker::SetTheThread(QThread* thread){
QObject::connect(thread,SIGNAL(started()),this,SLOT(MyStart()));
}
void MyHttpWorker::MyWake(){
pauseCond.wakeAll();
}
void MyHttpWorker::MyStart(){
qDebug() << "Start" ;
while(true){
syncPause.lock();
qDebug() << "thread waiting...";
pauseCond.wait(&syncPause);
qDebug() << "thread resumed.";
syncPause.unlock();
//sending the actual request here
QNetworkRequest myRequest;
myRequest.setUrl(QUrl("http://www.google.com"));
nam->get(myRequest);
}
}
main.cpp
#include <QCoreApplication>
#include <QThread>
#include <QDebug>
#include <myhttpworker.h>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
//create the worker, thread and launch it... (worker is waiting by default)
MyHttpWorker* worker = new MyHttpWorker;
QThread* httpThread = new QThread;
worker->SetTheThread(httpThread);
worker->moveToThread(httpThread);
httpThread->start();
//try and send 5 requests ...
for(int i=0;i<5;i++){
qDebug() << "Unpausing";
QThread::currentThread()->msleep(1000);
worker->MyWake();
}
return a.exec();
}

Answer 1

don't create an infinite loop but let the even loop handle it:
void MyHttpWorker::MyWake()
{
QMetaObject::invokeMethod(this,"doSend");
//send to the event loop
}
// new slot
void MyHttpWorker::doSend(){
//sending the actual request here
QNetworkRequest myRequest;
myRequest.setUrl(QUrl("http://www.google.com"));
nam->get(myRequest);
}
//and remove the myStart and all that synchronisation
then when you want to stop it just send a quit to the thread. I suggest you also connect the finished signal of the thread to the deleteLater slot of MyHttpWorker