[Development] Community effort in updating Qt5 docs -- QThread focus

[Chris Meyer]

On Sat, Sep 29, 2012 at 11:04 AM, João Abecasis <joao at abecasis.name> wrote:
> João Abecasis wrote:
>> Chris Meyer wrote:
>>> The documentation promotes the idea of using 'moveToThread' as a
>>> preferred threading mechanism. However, we've found that moveToThread
>>> is full of pitfalls.
>>>
>>> Particularly, an object must be deleted on the thread on which it
>>> resides. This makes it difficult to manage the lifetime of objects
>>> that have been moved to a thread via moveToThread. You need to
>>> configure an independent mechanism to delete objects that have been
>>> moved to thread (i.e. send a signal to the thread that it's about to
>>> shutdown and allow the objects to deleteLater within the thread, which
>>> also implies that you need to keep track of the objects that are
>>> within the thread, which somewhat defeats the apparent simplicity of
>>> moveToThread). Also, you cannot use the finished signal from the
>>> thread since the thread will already be gone by then.
>>
>> Since Qt 4.8 you can connect QThread::finished to QObject::deleteLater
>> and it should do the right thing in the appropriate thread.
>
> For reference, here's a link to the commit implementing this:
>
>     http://qt.gitorious.org/qt/qt/commit/0c643b179c5154c50b61dba421016b7b48794720
>

This looks like a great change to have. In any case, the overall
problem, solution, and in what version it was implemented needs to be
documented in the QThread documentation. I missed this
commit-log-message-as-documentation before.

>>> The bug will show up intermittently and differently on various
>>> platforms and is difficult to debug if you don't know about the
>>> problem. You'll just end up with spurious crashes (typically at quit
>>> time), especially for networking objects.
>
> Cheers,
>
>
> João