On quarta-feira, 3 de agosto de 2016 11:22:36 PDT Jorge Fierro wrote: > What exactly is the relationship between an event loop entered by > calling QEventLoop::exec() and *the* main event loop (the one running > when you can QCoreApplication::exec())?
Both functions as well as QThread::exec() are windows into the actual event dispatcher that runs behind the scenes. All three control the QAbstractEventDispatcher that either QCoreApplication or QThread creates. I think these two links answer your question best: https://code.woboq.org/qt5/qtbase/src/corelib/kernel/ qcoreapplication.cpp.html#_ZN16QCoreApplication4execEv (line 1258) https://code.woboq.org/qt5/qtbase/src/corelib/thread/ qthread.cpp.html#_ZN7QThread4execEv (line 506) As you can see, both QCoreApplication::exec or QThread::exec create a QEventLoop and call exec on it. The same is also true, for that matter, for QDialog::exec. > There are a number of related questions: > > - Does QEventLoop::exec() enter *the* main event loop? Or, > - Does QEventLoop::exec() enter a different event loop independent > from QCoreApplication::exec()? There's only one event dispatcher per thread. > - Can QEventLoop::exec() be called outside QCoreApplication::exec() > (i.e., in a call stack that didn't originate from QCoreApplication::exec())? Sure. You could even use QEventLoop::exec() in place of QCoreApplication::exec() in your main function or QThread::exec() in your run function. The two are very similar, but not identical. QCoreApplication's loop emits aboutToQuit and its descendant classes react to the last window closing, while QEventLoop does not. > - If QEventLoop::exec() spins the main loop then any event at all can > be generated. Is this why one must use it very carefully to avoid > reentrancy issues? Yes. Avoid nesting event loops like the plague. -- Thiago Macieira - thiago.macieira (AT) intel.com Software Architect - Intel Open Source Technology Center _______________________________________________ Interest mailing list Interest@qt-project.org http://lists.qt-project.org/mailman/listinfo/interest
