[Qt-interest] Create a new GUI Thread

[Luke Campagnola]

On Mon, Mar 2, 2009 at 18:56, David Johnson <david at usermode.org> wrote:

> The GUI parts of the application need to be in the same thread. It's a
> limitation on both X11 and Mac. There may be ways around this under
> Windows,
> but it is not supported and may break with new Qt releases.
>

I thought that might be the case, but I'm pretty surprised by it--why should
X11 care whether two windows are controlled by two separate processes or by
two threads in the same process?

But since QThreads can easily communicate with each other, there is very
> rarely a need for GUI elements to be in different threads. Have a worker
> thread do the heavy lifting, then communicate its results to the main GUI
> thread.
>

In my case, the majority of the heavy lifting is in GUI operations (ie
graphicsview updates--multiple scrolling plots and video displays). I've
already farmed out all of the non-GUI labor to other threads, but the GUI is
still too heavy for one core to handle efficiently.

Whether or not there is a real need to have multiple GUI threads, from an
application design standpoint it often makes a lot of sense. Separating a
GUI and the data it displays means there is added overhead in message
passing and a lot of extra programming.

To me, asking why you would want to have multiple GUI threads is like asking
why you would want to have multiple processes running in X. If you're only
using one program at a time, there's no need to have multiple processes at
all. As the system becomes more complex, it makes sense to logically divide
X control into multiple processes that draw into their own windows.
Likewise, the software I am writing is complex enough that it makes a lot of
sense to break the application up into components that operate independently
and draw their own GUI. The only difference for me is that my components
also need to exchange large amounts of data and at times must be able to
synchronize easily.

I'm stuck somewhere between using a slow, monolithic application and using
multiple applications communicating via IPC. Seems like right now there's
just no really elegant solution to the problem, although DBUS looks somewhat
promising if it can become a little less unix-centric..

Q
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