threads with gtk gui problem

[andy baxter]

On 14/05/11 14:12, Andy Baxter wrote:
> Hi,
>
> I'm working on adding a Gtk GUI to a python program. Its main function 
> is to read raw data from an arduino board over USB, and convert it to 
> MIDI note/controller events to be sent to another program. I've had it 
> working fine with just a command line interface, but when I replaced 
> the command line with a Gtk interface, I started having problems 
> getting the thread that reads the USB port to run.
>
> I'm not sure what the custom is on this list for pasting code - It's a 
> long program so I don't want to paste the whole thing.
>
> The sequence of events I've coded is:
>
> - the program starts.
> - the port reader thread (which is a threading.Thread subclass) is 
> initialised.
> - the object which controls the interface is initialised (i.e. the 
> glade file is loaded.)
> - the port reader is started (i.e. the 'start' method is called, which 
> calls the 'run' method in a thread).
> - then the gtk main loop is run.
>
> The behaviour I'm getting is that the port reader either fails to 
> start, or stops running at the point where it tries to initialise the 
> serial port. It then does nothing until I close the main window, at 
> which point it starts running again.
>
> The port reader's run method begins like this:
>
>    # the method called by the thread superclass to run the main loop 
> of the thread.
>    def run(self):
>       # main loop of thread.
>       print "Starting port reader."
>       fhan=serial.Serial(port=keeper.config['usbPort'], 
> baudrate=keeper.config['usbBaud'], timeout=0.1)
>       print "1"
>       fhan.open()
>       print "2"
>       seq=PySeq() # the sequencer library object
>       port=seq.createOutPort(keeper.config['midiPortName']) # make a 
> midi out port.
>       midich=keeper.config['midich']
>       print "3"
>       while True:
>          inbuf=[]
>          print ".",
>          char=fhan.read(1)
>          if self.quit:
>             fhan.close()
>             return
>          if len(char)==0: continue
>          ... (code to process the character read in)
>
> ('keeper' is a global object which stores the config data and 
> references to a few key objects).
>
> When you start the program, the thread stops either before the first 
> print statement, or on the line which initialises the serial port ( 
> fhan=serial.Serial(...) ). '1', '2', and '3' only get printed /after/ 
> you close the gtk main window.
>

I've verified that the problem is due to the gtk main loop interfering 
with the thread I've started. If I use this code:

if __name__ == "__main__":
    print "Starting mapper"
    keeper=Keeper() # initialise the keeper. (A global object which 
holds references to key objects)
    keeper.start() # tell the keeper to start the port reader.
    for n in xrange(10): # wait for 10 seconds.
       time.sleep(1)
       print "x"
    #gtk.main() # start the gtk main loop.
    keeper.stop() # tell the keeper to shut things down.

the program runs correctly. I.e. values are read from the usb port when 
they come in.

if I use this code:

if __name__ == "__main__":
    print "Starting mapper"
    keeper=Keeper() # initialise the keeper. (A global object which 
holds references to key objects)
    keeper.start() # tell the keeper to start the port reader.
    #for n in xrange(10):
    #   time.sleep(1)
    #   print "x"
    gtk.main() # start the gtk main loop.
    keeper.stop() # tell the keeper to shut things down.

The port reader thread blocks at the point it tries to open the serial 
port. I.e. 'Starting port reader' is printed straight away, but '1', 
'2', and '3'  are only printed after you close the gtk main window.