QApplication In Non-Main Thread

If you are using QThread then you already have normal Qt event loop and can just run exec() inside QThread::run() function. While you can't work with GUI objects outside of the main thread you still can interact with them through queued signal/slot connections. Maybe you can try to store pointer to the main thread QThread object and call QObject::moveToThread() to move your GUI objects to the main thread instead of moving QApplication into another thread.

I think it's not really good idea to try to go against toolkit with different kind of hacks and kluges.

You can start a QApplication in a PThread as below

//main.cpp

#include <iostream>
#include "appthread.h"
int main(int argc, char *argv[]) {
  InputArgs args = {argc, argv};
  StartAppThread(args);
  sleep(10);
  return 0;
}

//appthread.h

struct InputArgs{
  int argc;
  char **argv;
};
void StartAppThread(InputArgs &);

//appthread.cpp

#include <QApplication>
#include <QMainWindow>
#include <QPushButton>
#include "appthread.h"
#include <pthread.h>

void *StartQAppThread(void *threadArg) {
  InputArgs *args = (struct InputArgs*) threadArg;
  QApplication app(args->argc, args->argv);
  QMainWindow w;
  w.show();
  w.setCentralWidget(new QPushButton("NewButton"));
  app.exec();
  pthread_exit(NULL);
}

void StartAppThread(InputArgs &args) {
  pthread_t thread1;  
  int rc = pthread_create(&thread1, NULL, StartQAppThread, (void*)&args);
}