QtSingleApplication crash

[xiaofeng]

Re: QLocalServer crashes when QString is used instead of "string_literal"

qt version: 5.6.1
qtsingleapplication version: 2.6.1

1  __strlen_sse2_pminub                                                                   0x7ffff5173e71 
2  QCoreApplication::arguments()                                                          0x7ffff62ea2fd 
3  sm_performSaveYourself(QXcbSessionManager *)                                           0x7fffe4d19470 
4  sm_saveYourselfCallback(_SmcConn *, void *, int, int, int, int)                        0x7fffe4d19fe5 
5  _SmcProcessMessage                                                                     0x7fffedb9ec4d 
6  IceProcessMessages                                                                     0x7fffeddb2ab7 
7  QMetaObject::activate(QObject *, int, int, void * *)                                   0x7ffff630ece1 
8  QSocketNotifier::activated(int, QSocketNotifier::QPrivateSignal)                       0x7ffff638067e 
9  QSocketNotifier::event(QEvent *)                                                       0x7ffff631b809 
10 QApplicationPrivate::notify_helper(QObject *, QEvent *)                                0x7ffff6d30bec 
11 QApplication::notify(QObject *, QEvent *)                                              0x7ffff6d355b2 
12 QCoreApplication::notifyInternal2(QObject *, QEvent *)                                 0x7ffff62e6d86 
13 socketNotifierSourceDispatch(_GSource *, int ( *)(void *), void *)                     0x7ffff6334ca0 
14 g_main_context_dispatch                                                                0x7ffff4070d7a 
15 g_main_context_iterate.isra.24                                                         0x7ffff40710b8 
16 g_main_context_iteration                                                               0x7ffff407116c 
17 QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)             0x7ffff633409c 
18 QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>)                                0x7ffff62e58eb 
19 QCoreApplication::exec()                                                               0x7ffff62ed426 
20 main                                                                       main.cpp 88 0x45bdce       

[ambershark]

I think I know what's going on. Can I see your main?

[ambershark]

@xiaofeng Nevermind I see the code in the thread you linked, and confirmed my suspicion.

SingleInstance::SingleInstance(int argc, char *argv[]) :
    QApplication(argc, argv),
    mServerName("foo")
{

If you see here SingleInstance takes an int argc instead of int &argc, any argc passed to QApplication needs to be modifiable and as it's a reference. Change your definition to int &argc and your crash will be gone.

[xiaofeng]

@ambershark Thanks so much. I didn't recognize it's an int &argc for so many years, thanks.

[ambershark]

@xiaofeng Don't worry, it got me too. That's how I knew what was going on, lol. It was not an easy bug to find either. I'm not sure why they do the int &, but it causes some real problems for people. :)

[kshegunov]

@ambershark said in qtsingleapplication crash:

I'm not sure why they do the int &

Because QCoreApplication processes and possibly modifies the command line, as it has its own set of flags it responds to.

[ambershark]

@kshegunov Ah that makes a lot of sense. I figured they had a good reason for it. Qt is well thought out. :)

[kshegunov]

@ambershark said in qtsingleapplication crash:

Qt is well thought out.

Most of it anyway ;P