Python, GTK and background threads

Roken · 2012-05-26 16:38:47

OK, I'm still new to python (but my teeth on COBOL a long long time ago), and whilst I can usually battle through existing scripts and figure out what's going on, I'm trying to add functionality to one of my own and no idea how to do it.

I have a python script that launches an external process (os.popen) and then opens a gtk window. The gtk works just fine and does what it's supposed to. However, I want to add a thread that will check whether or now the external program is running and if it's finished, automatically destroy the gtk window and exit the script. However, to get the gtk window I obviously have to call gtk.main, which prevents me from launching my own loop testing the other program.

incidentally, my test is based on

child = os.popen("ExternalProgram")
....
....
....

if child.poll() == None:
    .....

And I'm not even sure that's the correct way to test (haven't been able to even start testing yet) so perhaps if someone could give me a heads up on that, too

Any idea?

TIA

drcouzelis · 2012-05-26 17:05:37

Just a quick thought: How about reversing the dependancy? Instead, make the GTK application check to see if it's ready to quit. Then, when it quits, your original application will continue running.

Edit: In before Lunar shows up and tells you how to REALLY do it.

Last edited by drcouzelis (2012-05-26 17:05:59)

lunar · 2012-05-26 17:10:56

Here I am

"os.popen" and related functions have been superseded by the "subprocess" module. Use "subprocess.Popen" to spawn processes.

Wrap the invocation of the background task in a separate class – let's call it "BackgroundWorker" for now – that spawns a background thread which in turn executes the process via "subprocess.call()" and emits a "finished" signal when the process terminated. Create an instance of this class in In "MyWindow.__init__()" (where "MyWindow" is derived from "Gtk.Window") and connect the "BackgroundWorker.finished" signal to a callback which closes the window. In the entry point of your script create an instance of "MyWindow", show it and start the Gtk main loop.

Before that, read the documentation of Gtk and look for a class that wraps background processes, like "QProcess" does in Qt. I don't know if such a class exists in Gtk but if it does it'll significantly ease working with subprocesses in a GUI.

Last but not least a general and very important note concerning threads and GUIs: Do never access any GUI element directly from background thread!

Last edited by lunar (2012-05-26 17:11:25)

ewaller · 2012-05-26 17:19:16

Why use a thread? How about a simple periodic timer with a callback. It all happens in the same thread.

lunar · 2012-05-26 18:04:57

@ewaller: Polling kills power-saving. If you want your laptop battery to last, avoid it

Roken · 2012-05-27 15:17:36

Thank you. Gives me something to work with, though I have to admit that the documentation I've seen thus far isn't the most enlightening, but it's more that I had before. Not marking solved just yet - but I'll be sure to report back

Arch Linux

#1 2012-05-26 16:38:47

Python, GTK and background threads

#2 2012-05-26 17:05:37

Re: Python, GTK and background threads

#3 2012-05-26 17:10:56

Re: Python, GTK and background threads

#4 2012-05-26 17:19:16

Re: Python, GTK and background threads

#5 2012-05-26 18:04:57

Re: Python, GTK and background threads

#6 2012-05-27 15:17:36

Re: Python, GTK and background threads

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