[Crash] tst_examples crashes on X11 CI machine due to threaded renderer

0xb7fe2430 in __kernel_vsyscall ()
(gdb) bt
#0  0xb7fe2430 in __kernel_vsyscall ()
#1  0xb540d651 in *__GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#2  0xb5410a82 in *__GI_abort () at abort.c:92
#3  0xb5406718 in *__GI___assert_fail (assertion=0xb572a2c5 "ret != inval_id", file=0xb572a289 "../../src/xcb_io.c", line=385, function=0xb572a444 "_XAllocID") at assert.c:81
#4  0xb56bac29 in _XAllocID () from /usr/lib/libX11.so.6
#5  0xb568f9e3 in XCreateGC () from /usr/lib/libX11.so.6
#6  0xb58aa095 in ?? () from /usr/lib/mesa/libGL.so.1
#7  0xb588881e in ?? () from /usr/lib/mesa/libGL.so.1
#8  0xb5888b09 in glXMakeCurrentReadSGI () from /usr/lib/mesa/libGL.so.1
#9  0xb5888f33 in glXMakeCurrent () from /usr/lib/mesa/libGL.so.1
#10 0xb79d765d in QGLContext::makeCurrent (this=0xace7c858) at qgl_x11.cpp:932
#11 0xb793bb0c in QGLWidget::makeCurrent (this=0xbffff00c) at qgl.cpp:4023
#12 0xb6326298 in QSGCanvasRenderThread::run (this=0xad20df30) at items/qsgcanvas.cpp:2008
#13 0xb597873b in QThreadPrivate::start (arg=0xad20df30) at thread/qthread_unix.cpp:298
#14 0xb585c96e in start_thread (arg=0xafcffb70) at pthread_create.c:300
#15 0xb54b0a4e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130
(gdb) thread 1
[Switching to thread 1 (Thread 0xb4cff720 (LWP 23145))]#0  0xb7fe2430 in __kernel_vsyscall ()
(gdb) bt
#0  0xb7fe2430 in __kernel_vsyscall ()
#1  0xb5861015 in pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/pthread_cond_wait.S:122
#2  0xb56a0324 in ?? () from /usr/lib/libX11.so.6
#3  0xb569fd10 in ?? () from /usr/lib/libX11.so.6
#4  0xb56bab73 in _XIDHandler () from /usr/lib/libX11.so.6
#5  0xb56b377e in ?? () from /usr/lib/libX11.so.6
#6  0xb5698353 in XGetWindowProperty () from /usr/lib/libX11.so.6
#7  0xb6e49e62 in GetMWMHints (display=0x80f7d90, window=62915282) at kernel/qwidget_x11.cpp:145
#8  0xb6e5156f in QWidgetPrivate::show_sys (this=0xacfbaec8) at kernel/qwidget_x11.cpp:1940
#9  0xb6df0076 in QWidgetPrivate::show_helper (this=0xacfbaec8) at kernel/qwidget.cpp:7536
#10 0xb6df08d8 in QWidget::setVisible (this=0xbffff00c, visible=true) at kernel/qwidget.cpp:7750
#11 0x08058a82 in QWidget::show (this=0xbffff00c) at ../../../../../qtbase/include/QtGui/../../src/gui/kernel/qwidget.h:494
#12 0x08058014 in tst_examples::sgexamples (this=0xbffffa0c) at tst_examples.cpp:243
#13 0x080581cc in tst_examples::qt_static_metacall (_o=0xbffffa0c, _c=QMetaObject::InvokeMetaMethod, _id=3, _a=0xbffff0e0) at .moc/debug-shared/tst_examples.moc:57
#14 0xb5ab6814 in QMetaMethod::invoke (this=0xbffff24c, object=0xbffffa0c, connectionType=Qt::DirectConnection, returnValue=..., val0=..., val1=..., val2=..., val3=..., val4=..., val5=..., val6=..., val7=..., val8=..., val9=...)
    at kernel/qmetaobject.cpp:1636
#15 0xb5ab5c36 in QMetaObject::invokeMethod (obj=0xbffffa0c, member=0x8128a08 "sgexamples", type=Qt::DirectConnection, ret=..., val0=..., val1=..., val2=..., val3=..., val4=..., val5=..., val6=..., val7=..., val8=..., val9=...)
    at kernel/qmetaobject.cpp:1178
#16 0xb7fbf30a in QMetaObject::invokeMethod (obj=0xbffffa0c, member=0x8128a08 "sgexamples", type=Qt::DirectConnection, val0=..., val1=..., val2=..., val3=..., val4=..., val5=..., val6=..., val7=..., val8=..., val9=...)
    at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs.h:418
#17 0xb7fbc8d1 in qInvokeTestMethodDataEntry (slot=0x8128a08 "sgexamples") at qtestcase.cpp:1355
#18 0xb7fbcec7 in qInvokeTestMethod (slotName=0x807a03b "sgexamples()", data=0x0) at qtestcase.cpp:1463
#19 0xb7fbd57c in qInvokeTestMethods (testObject=0xbffffa0c) at qtestcase.cpp:1612
#20 0xb7fbddbd in QTest::qExec (testObject=0xbffffa0c, argc=2, argv=0xbffffae4) at qtestcase.cpp:1851
#21 0x080580dd in main (argc=2, argv=0xbffffae4) at tst_examples.cpp:248