[Interest] QDBusConnection::sessionBus() : caching required?

[René J. V. Bertin]

Thiago Macieira wrote:

> You can call multiple times and you'll always get the same connection.

OK, thanks.

Here's another observation (& backtrace) potentially to be taken into account 
for your fix: when I don't get a crash-on-exit I often get a deadlock like so:

  * frame #0: 0x00007fff85129716 libsystem_kernel.dylib`__psynch_cvwait + 10
    frame #1: 0x00007fff8af34c3b libsystem_pthread.dylib`_pthread_cond_wait + 
727
    frame #2: 0x0000000112abc77b 
QtCore`QWaitConditionPrivate::wait(this=0x00007fda59e5a300, time=<unavailable>) 
+ 75 at qwaitcondition_unix.cpp:136
    frame #3: 0x0000000112abc62b 
QtCore`QWaitCondition::wait(this=0x00007fda59e517d8, mutex=0x00007fda59e517d0, 
time=18446744073709551615) + 155 at qwaitcondition_unix.cpp:208
    frame #4: 0x0000000112ab683f 
QtCore`QSemaphore::acquire(this=0x00007fff50614d38, n=1) + 79 at 
qsemaphore.cpp:137
    frame #5: 0x0000000112cadc13 
QtCore`QMetaObject::activate(sender=0x00007fda59c56500, 
signalOffset=<unavailable>, local_signal_index=<unavailable>, 
argv=<unavailable>) + 2499 at qobject.cpp:3698
    frame #6: 0x000000011134f280 
QtDBus`QDBusConnectionPrivate::signalNeedsDisconnecting(this=<unavailable>, 
_t1=<unavailable>, _t2=<unavailable>) + 64 at moc_qdbusconnection_p.cpp:345
    frame #7: 0x00000001113135ff 
QtDBus`QDBusConnectionPrivate::disconnectSignal(this=0x00007fda59c56500, 
service=<unavailable>, path=<unavailable>, interface=<unavailable>, 
name=<unavailable>, argumentMatch=<unavailable>, signature=<unavailable>, 
receiver=<unavailable>, slot=<unavailable>) + 287 at qdbusintegrator.cpp:2188
    frame #8: 0x00000001113008fb QtDBus`QDBusConnection::disconnect(QString 
const&, QString const&, QString const&, QString const&, QObject*, char const*) 
[inlined] QStringList::QStringList(this=0x0000000112eed470, 
this=0x0000000112eed470, this=0x0000000112eecc30, this=0x0000000112eecc30, 
argumentMatch=0x0000000112eed470, signature=0x0000000112eecc30, 
receiver=<unavailable>) + 158 at qdbusconnection.cpp:864
    frame #9: 0x000000011130085d 
QtDBus`QDBusConnection::disconnect(this=0x00007fda5c51b9e0, 
service=0x00007fff50614ff8, path=0x00007fff50614ff0, 
interface=0x00007fff50614fe8, name=0x00007fff50614fe0, 
receiver=0x00007fda5a191000, slot=0x000000011f0532d8) + 29 at 
qdbusconnection.cpp:822
    frame #10: 0x000000011eff0e88 
qtcurve.so`QtCurve::Style::disconnectDBus(this=0x00007fda5a191000) + 168 at 
qtcurve.cpp:712
    frame #11: 0x000000011f029e96 
qtcurve.so`QtCurve::StylePlugin::~StylePlugin() [inlined] 
QtCurve::runAllCleanups() + 13 at qtcurve_plugin.cpp:86
    frame #12: 0x000000011f029e89 
qtcurve.so`QtCurve::StylePlugin::~StylePlugin() [inlined] 
QtCurve::StylePlugin::~StylePlugin(this=<unavailable>) + 16 at 
qtcurve_plugin.cpp:167
    frame #13: 0x000000011f029e79 
qtcurve.so`QtCurve::StylePlugin::~StylePlugin() [inlined] 
QtCurve::StylePlugin::~StylePlugin(this=<unavailable>) at qtcurve_plugin.cpp:166
    frame #14: 0x000000011f029e79 
qtcurve.so`QtCurve::StylePlugin::~StylePlugin(this=<unavailable>) + 9 at 
qtcurve_plugin.cpp:166
    frame #15: 0x0000000112c6e24d 
QtCore`QLibraryPrivate::unload(this=0x00007fda59e51230, flag=NoUnloadSys) + 93 
at qlibrary.cpp:551
    frame #16: 0x0000000112c66d48 
QtCore`QFactoryLoaderPrivate::~QFactoryLoaderPrivate(this=0x00007fda59e50ca0) + 
88 at qfactoryloader.cpp:88
    frame #17: 0x0000000112c6714e 
QtCore`QFactoryLoaderPrivate::~QFactoryLoaderPrivate() [inlined] 
QFactoryLoaderPrivate::~QFactoryLoaderPrivate(this=0x00007fda59e50ca0) + 14 at 
qfactoryloader.cpp:85
    frame #18: 0x0000000112c67149 
QtCore`QFactoryLoaderPrivate::~QFactoryLoaderPrivate(this=0x00007fda59e50ca0) + 
9 at qfactoryloader.cpp:85
    frame #19: 0x0000000112ca5801 QtCore`QObject::~QObject() [inlined] 
QScopedPointerDeleter<QObjectData>::cleanup(pointer=<unavailable>) + 2033 at 
qscopedpointer.h:54
    frame #20: 0x0000000112ca57f6 QtCore`QObject::~QObject() [inlined] 
QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> 
>::~QScopedPointer() + 4 at qscopedpointer.h:101
    frame #21: 0x0000000112ca57f2 QtCore`QObject::~QObject() [inlined] 
QScopedPointer<QObjectData, QScopedPointerDeleter<QObjectData> 
>::~QScopedPointer() at qscopedpointer.h:99
    frame #22: 0x0000000112ca57f2 QtCore`QObject::~QObject(this=<unavailable>) + 
2018 at qobject.cpp:1042
    frame #23: 0x0000000112c6928e QtCore`QFactoryLoader::~QFactoryLoader() 
[inlined] QFactoryLoader::~QFactoryLoader(this=0x00007fda59e2a3a0) + 14 at 
qfactoryloader.cpp:227
    frame #24: 0x0000000112c69289 
QtCore`QFactoryLoader::~QFactoryLoader(this=0x00007fda59e2a3a0) + 9 at 
qfactoryloader.cpp:227
    frame #25: 0x0000000111b93616 QtWidgets`(anonymous 
namespace)::Q_QGS_loader::innerFunction()::Cleanup::~Cleanup() [inlined] 
(anonymous namespace)::Q_QGS_loader::innerFunction()::Cleanup::~Cleanup() + 18 
at qstylefactory.cpp:70
    frame #26: 0x0000000111b93604 QtWidgets`(anonymous 
namespace)::Q_QGS_loader::innerFunction(this=<unavailable>)::Cleanup::~Cleanup() 
+ 4 at qstylefactory.cpp:70
    frame #27: 0x00007fff8342d7b5 libsystem_c.dylib`__cxa_finalize + 177


That one goes away when I simply don't disconnect (but that apparently sometimes 
led to segfaults on Linux when events came in after the receiver was deleted 
(and the style plugin was already dlclose'd)).

R.