NM-Qt: tens of blocking DBus calls for every nm device

[Aleix Pol]

Hi networkmanagerers, plasmers,
I have been looking into what kind of things happen between the plasma
shell is booted and actually starts.
An obvious way to check where we're blocking, is by seeing who is
making blocking dbus calls. Adding a breakpoint to whenever there's a
blocking dbus call goes lengths.

A big pain point I've found is nm-qt's Device initialization.

Maintainers, do you think it would be possible to lazily fetch these
values instead of just populating everything upon construction? I'm
positive it would have an immediate impact.
I see few solutions:
- Just using QDBusPendingReply so it will issue the call and only
block when the value is actually read.
- Issue a dbus call that gets all properties at once
(org.freedesktop.DBus.Properties.GetAll). It will still block, but
less.
- Only ask for the value when requested, not before. Then it's
probably less bad to block.

HTH,
Aleix

[1]
#0 QDBusConnection::call() at
/home/apol/devel/frameworks/qt5/qtbase/src/dbus/qdbusconnection.cpp:689
#1 QDBusAbstractInterfacePrivate::property() at
/home/apol/devel/frameworks/qt5/qtbase/src/dbus/qdbusabstractinterface.cpp:179
#2 QDBusAbstractInterfaceBase::qt_metacall() at
/home/apol/devel/frameworks/qt5/qtbase/src/dbus/qdbusabstractinterface.cpp:290
#3 QDBusAbstractInterface::qt_metacall() at
/home/apol/build-devel/qt5/qtbase/src/dbus/.moc/moc_qdbusabstractinterface.cpp:97
#4 OrgFreedesktopNetworkManagerDeviceInterface::qt_metacall() at
/home/apol/build-devel/frameworks/networkmanager-qt/src/moc_nm-deviceinterface.cpp:248
#5 QMetaProperty::read(QObject const*) const() at
/home/apol/devel/kde5/lib/libQt5Core.so.5
#6 QObject::property(char const*) const() at
/home/apol/devel/kde5/lib/libQt5Core.so.5
#7 OrgFreedesktopNetworkManagerDeviceInterface::managed() at
/home/apol/devel/frameworks/networkmanager-qt/src/dbus/nm-deviceinterface.h:155
#8 NetworkManager::DevicePrivate::DevicePrivate() at
/home/apol/devel/frameworks/networkmanager-qt/src/device.cpp:112
#9 NetworkManager::Device::Device() at
/home/apol/devel/frameworks/networkmanager-qt/src/device.cpp:198
#10 NetworkManager::NetworkManagerPrivate::createNetworkInterface() at
/home/apol/devel/frameworks/networkmanager-qt/src/manager.cpp:287
#11 NetworkManager::NetworkManagerPrivate::findRegisteredNetworkInterface()
at /home/apol/devel/frameworks/networkmanager-qt/src/manager.cpp:254
#12 NetworkManager::NetworkManagerPrivate::networkInterfaces() at
/home/apol/devel/frameworks/networkmanager-qt/src/manager.cpp:360
#13 NetworkManager::networkInterfaces() at
/home/apol/devel/frameworks/networkmanager-qt/src/manager.cpp:936
#14 ConnectionIcon::ConnectionIcon() at
/home/apol/devel/frameworks/plasma-nm/libs/declarative/connectionicon.cpp:63
#15 QQmlPrivate::QQmlElement<ConnectionIcon>::QQmlElement() at
/home/apol/devel/kde5/include/QtQml/qqmlprivate.h:99
#16 QQmlPrivate::createInto<ConnectionIcon>() at
/home/apol/devel/kde5/include/QtQml/qqmlprivate.h:108
#17 QQmlType::create() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlmetatype.cpp:761
#18 QQmlObjectCreator::createInstance() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlobjectcreator.cpp:1057
#19 QQmlObjectCreator::setPropertyBinding() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlobjectcreator.cpp:738
#20 QQmlObjectCreator::setupBindings() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlobjectcreator.cpp:690
#21 QQmlObjectCreator::populateInstance() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlobjectcreator.cpp:1325
#22 QQmlObjectCreator::createInstance() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlobjectcreator.cpp:1183
#23 QQmlObjectCreator::create() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlobjectcreator.cpp:200
#24 QQmlIncubatorPrivate::incubate() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlincubator.cpp:301
#25 QQmlIncubationController::incubateFor() at
/home/apol/devel/frameworks/qt5/qtdeclarative/src/qml/qml/qqmlincubator.cpp:394
#26 KDeclarative::QmlObjectIncubationController::incubate() at
/home/apol/devel/frameworks/kdeclarative/src/kdeclarative/private/qmlobject_p.h:63