[Interest] moveToThread and object deletion

[Thiago Macieira]

On sexta-feira, 15 de março de 2013 00.33.23, Etienne Sandré-Chardonnal wrote:
> Thanks for the answer. This leads me to two questions:
> 1) It's then unsafe to destroy the QThread in a slot connected to
> "finished", as it is in fact "aboutToFinish", am I right? But deleting
> after terminate() signal or after return from wait() is safe.

Correct. Deleting the sender of a signal in a slot called through a 
DirectConnection is almost always a bad idea. You never know what it's going 
to do after the signal is emitted. In particular, it's a very bad idea to do 
this to a QThread, starting with the fact that you can't delete a QObject-
derived class from any other thread than its owning thread.

You can delete it in a slot called via QueuedConnection or you can queue the 
deletion by calling deleteLater().

> 2)One poorly documented thing about QThread, is where are supposed to be
> called exit() and quit(). While exit() naming suggests that it should be
> called from the thread to terminate as in posix, the slot nature of quit()
> suggests it should be called from the thread where QThread lives, ie the
> parent thread. But quit calls exit(0). That's confusing...

Indeed. In older versions, they could only be called from the thread that 
QThread started, even if they were methods in a QObject. That was 
inconsistent.

In recent versions (since 4.6 or so), you can call them from any thread.

> In other words, is it safe/clean to:
>  - call this->thread()->quit()   (quit called from the thread)
> or
>  - call workerThread->quit()   (quit called from the parent thread where
> QThread lives)

Yes, both are fine.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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