QThreadPipe: internal error, wakeUps.testAndSetRelease(1, 0) failed! with Qt without glib

Hi,

I have detected a bug in QtBase when Qt is not compiled with glib support for event loop. The problem occurs when a program in using thread with event loop, is working as daemon (and when we are writing log in stderr.

I built a small application that reproduct the problem available here with all compilation steps : https://github.com/Jet1oeil/qt-test-service

After some investigation, i found that the problem probably concern the lines in qeventdispatcher_unix.cpp arround line 121.

 
# ifndef QT_NO_EVENTFD
if ((fds[0] = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC)) >= 0) {
qWarning("QThreadPipe:::init fd[0]=%d, fd[1]=%d", fds[0], fds[1]); return true; {color}}
# endif
In my observation, this function may return a file descriptor where value is 2 (stderr), and the problem is that when writing in stderr this issues a lot of events. I'm not able to tell if this is normal, to get an fd with value 2 or if it's a kernel bug.

And after this, we encounter multiple an infinite loop issuing this log.
QThreadPipe: internal error, wakeUps.testAndSetRelease(1, 0) failed!
{{}}

Note that is problem happend randomly depending if the fd is 2 or not, which in my case happend 4/5 times.

You will find in attachement two logs with a more verbose qt version, one  where we obtain an fd = 2, and one where fd is not 2.

I hope i'm clear, I'm available for any question and help to fix this.

Regards,