[PyKDE] Re: Threading problem with PyQt4 and Macosx

[Phil Thompson]

On Saturday 24 February 2007 12:42 am, Matt Newell wrote:
> On Friday 23 February 2007 14:34, Matt Newell wrote:
> > On Friday 23 February 2007 12:52, Matt Newell wrote:
> > > On Friday 23 February 2007 12:38, Michael Guntsche wrote:
> > > > On Feb 23, 2007, at 20:43, Matt Newell wrote:
> > >
> > > ...
> > >
> > > > Hello Matt,
> > > >
> > > > Can you try and change the connect to a QueuedConnection? It looks
> > > > like it is using a "DirectConnection" now.
> > > > I was sure I tried that before, but back then I was using events and
> > > > not signals.
> > >
> > > It's already (correctly) using a queued connection to send the signal.
> > > I've already tracked it down further and eliminated one of the deadlock
> > > code paths by putting a /ReleaseGIL/ annotation on QLabel::setText.
> > > There is another deadlock though happening in the connect call which
> > > i'm tracking down now.
> > >
> > > > I tried it on my computer, but although the "connect" returns True I
> > > > do not get the emitted signal in my main thread.
> > > > I do not understand why.
> > >
> > > Hmm, i'm not sure why that would happen.
> >
> > So here's the deal.  In order to avoid deadlocks we must avoid running
> > any Qt code that will require a lock while the GIL is locked.  This is
> > because we can't avoid the opposite, which is acquiring the GIL while Qt
> > is holding a lock( For example Qt holds a lock while copying signal data
> > for queued connections, and we have to run python code for that. )  To
> > avoid a deadlock we must avoid one or the other.
> >
> > This means that any Qt calls that do a connect, or create/destroy any
> > qobjects must first release the GIL.  There may be other code paths in Qt
> > that require the same care.
> >
> > Try testing with this patch, it eliminates all deadlocks for me.
>
> I still get deadlocks when destroying the threads unless I add /ReleaseGIL/
> to the QThread dtor.
>
> I think that right now there are many potential deadlocks in PyQt.  All
> QObject and derived classes need their ctors and dtors marked /ReleaseGIL/.
> All connect/disconnect functions, any functions that indirectly delete or
> create qobjects, etc.  Essentially the entire api needs to be reviewed.

In the meantime you could try changing PyQt's configure.py (in 
set_sip_flags()) so that it invokes sip with the -g flag.

Phil