[Interest] Help, I'm in QML signal hell

Jason H jhihn at gmx.com
Mon Nov 4 17:32:43 CET 2019

Well, it's as single threaded as it can be, and I think that is the problem. The emits are direct invocations.  The problem arises when I want to simulate the communications - the comms with other systems won't happen the same way as if I pretend to get a reply.

For what I am running into, there is a remote system that is being communicated with. I can be connected to it, but I can't be connected all the time, so I have a look up of request:response. instead of doing the actual i/o I pretend to get the response back:
if (dummyMode == InDummyMode) {
	Message m = Message::parse(message);
	QByteArray reply = dummyReplies.contains(m.op) ? dummyReplies[m.op]: "";
	if (reply.length()) {
		qDebug() << Q_FUNC_INFO << "dummy reply" << reply;
		emit received(reply);

However in the live system the direct invocation does not occur, this creates differences in the signal emission order between the dummy and the real system. For whatever reason, the handlers get inverted. I need to find a way to not have them switch order. I cant start Function 10 (STF10) before I've passed function 9 (PSF09). Passing 9 is what starts 10.

> Sent: Friday, November 01, 2019 at 11:45 AM
> From: "Giuseppe D'Angelo via Interest" <interest at qt-project.org>
> To: interest at qt-project.org
> Subject: Re: [Interest] Help, I'm in QML signal hell
> Il 01/11/19 17:42, Jason H ha scritto:
> > I am using signals/slots in QML and the signal emissions are getting inverted.
> >
> > Here's my example:
> > bool Socket::emitSignalForOp(const QByteArray &) "STF10" 10
> > bool Socket::emitSignalForOp(const QByteArray &) "PSF09" 11
> >
> > STF10 necessarily comes after PSF09. In wall-clock time it does. But Qt is not getting the order right. The number above is the signal emission number, so it's not a display issue.
> You need to share more about your code.
> Just a word of caution: if we're talking about multithreaded code, "wall
> clock time" does simply not exist. Threads are relativistic...
> My 2 c,
> --
> Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
> KDAB (France) S.A.S., a KDAB Group company
> Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
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