如何在Qt的主事件循环中使用std :: thread？

Question

In this code Qt part (fun1()) always crashes. It writes:

terminate called without an active exception
Aborted (core dumped)

What should be wrong? When I call Qt stuff in main, and I do not use threads it works well, but I need to call another function and use threads (fun2() is just for ilustration) My code is here:

#include "../common/main_window.hpp"
#include <QtGui/QApplication>
#include <QtGui>

#include <thread>
#include <iostream>

int argc_;
char **argv_;

void fun1()
{
    QApplication a(argc_,argv_);
    MainWindow w;
    w.show();
    a.exec();
}

void fun2()
{
    std::cout << "Print something" << std::endl;
}

int main(int argc, char **argv)
{
    //argc_ = malloc((1)*sizeof(char*));
    argc_= argc;
    argv_= argv;

    std::thread first(fun1);
    std::thread second(fun2);

    return 0;
}

Answer 1

Main Thread

Qt does not support running the GUI event loop in any thread but the main thread. What you do happens to work on Windows, and might work on some Unixes, but it will never work on OS X or iOS, for example. So, in production code, there's no place for you running the threads like you do.

fun1() should be called from main , and you must wait for the other thread's functor to finish before you destruct the thread.

int fun1(int & argc, char ** argv)
{
  // QApplication might modify argc, and this should be fed back to
  // the caller.
  QApplication a(argc, argv);
  MainWindow w;
  w.show();
  return a.exec();
}

int main(int argc, char **argv)
{
  std::thread worker(fun2);
  int rc = fun1(argc, argv);
  worker.join();
  return rc;
}

Include Issues

Never include through <QtModule/Class> . This hides the configuration mistakes in your project file. You should either include individual classess one-by-one, or include the entire module's declarations in one go.

Thus, your test case should have either of the two following include styles:

#include <QtGui> // Qt 4 only
#include <QtWidgets> // Qt 5 only

or

#include <QApplication> // Qt 4/5
#include <Q....> // etc.

Answer 2

The actual reason why your program crashes is that std::thread throws exception in it's destructor if thread was neither joined nor detached.

To avoid the crash, you need to join your both threads.

Answer 3

Your main function returns after creating the threads, causing your program to exit and terminating all running threads. Call join on both threads so the main function doesn't return until the threads terminate by themselves.