如何启动在应用程序退出时不会关闭的线程？ （Qt C ++）

Question

I'm making an application for Mac OS X in Qt, and wanted to spawn a thread that doesn't close on application close.

Is this possible? If so, how? I don't want the process to be stopped if a user force quits the application.

Thanks in advance.

Note: If this is not possible, is there any way I can make this happen? (Maybe with calling a command in bash?)

Answer 1

it's possible to achieve your goal by initiating a new process via QProcess::startDetached, as per documents http://doc.qt.io/qt-4.8/qprocess.html#startDetached

Starts the program program with the arguments arguments in a new process, and detaches from it. Returns true on success; otherwise returns false. If the calling process exits, the detached process will continue to live .

Unix: The started process will run in its own session and act like a daemon.

Edit:

Here is an example for MacOS

// run start script
QString scriptPath = "path-to-start-script/start.sh" ;
QString cmd = "open -a " + scriptPath;
QProcess::startDetached(cmd);

Answer 2

When you terminate a process, all threads within that process die - the process is the thread "container". If you want to spawn something that lives on beyond your current process, then spawn a new independant process.

Answer 3

If your user force-quits the application, that usually means that they want to control the energy or resource expenditure on their system. Thinking that you know better than the user would be rather in the user's face. Don't anger your users :)

All you really want is:

1. For the process to survive quitting it through normal means (pressing ⌘-Q, selecting Quit from the menu, closing the last window, etc.).
2. For the dock icon to disappear after the GUI has been quit, as is the normal and expected behavior.
3. For a cleanup code to run after the GUI has vanished.

To that effect, you only need to hide the dock icon/menubar and then perform the cleanup:

main.mm

// https://github.com/KubaO/stackoverflown/tree/master/questions/hidedock-39378276
#include <QtWidgets>
#include <AppKit/AppKit.h>

void hideDockIcon() {
    [NSApp setActivationPolicy: NSApplicationActivationPolicyProhibited];
}

int main(int argc, char ** argv) {
    QApplication app{argc, argv};
    QLabel label{"Quit Me"};
    label.setMinimumSize(200, 100);
    label.show();
    int rc = app.exec();
    hideDockIcon();
    qDebug() << "cleaning up";
    QThread::sleep(5);
    qDebug() << "cleanup finished";
    return rc;
}

hidedock-39378276.pro

QT = widgets
CONFIG += c++11
TARGET = hidedock-39378276
TEMPLATE = app
OBJECTIVE_SOURCES += main.mm
LIBS += -framework AppKit

Answer 4

If u mean closing of Gui window by "Application Close" then it can be done easily...

#include "MainWindow.h"
#include <QApplication>

//////////////////////////////////////
#include <thread>
struct blabla {
    std::thread th;
    blabla():th([]{
        // body of your thread  
    }) {}
    ~blabla(){
        if(th.joinable())
            th.join();
    }   
} singleton_obj;
/////////////////////////////////////

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

Now the applicaton window will quit but the daemon thread will run n background... Enjoy