Re: [Discuss-gnuradio] matplotlib runtime error

[Marcus Müller]

Hi Activecat,

typical GUI problem; background is that X applications are inherently hard to multithread, which basically requires graphical toolkits to run in a main loop. This conflicts with every block being run in its own thread.

The easiest solution nowadays should be that you generate a QT flow graph in GRC, use PyQT to generate your GUI, register a message handler and integrate matplotlib (there are examples out there, just don't have one at my fingertips right now), and use the message passing interface to get data out of your flow graph into your GUI.

Greetings,

Marcus

On Fri, May 2, 2014 at 2:17 PM, Activecat <address@hidden> wrote:

Gurus,

I try to transfer an image file via a pair of USRPs.
At the receiver side, the data is fed into a custom block, where it plots the image in realtime using matplotlib's pyplot.imshow().

Unfortunately, in the work() function, the pyplot.draw() causes below runtime error.

handler caught exception: main thread is not in main loop
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gateway.py", line 55, in eval
    try: self._callback()
  File "/usr/local/lib/python2.7/dist-packages/gnuradio/gr/gateway.py", line 160, in __gr_block_handle
    ) for i in self.__out_indexes],
  File "/usr/local/lib/python2.7/dist-packages/activecat/image_sink1.py", line 72, in work
    self.axes1.figure.canvas.draw()  #pyplot.draw()
  File "/usr/lib/pymodules/python2.7/matplotlib/backends/backend_tkagg.py", line 349, in draw
    tkagg.blit(self._tkphoto, self.renderer._renderer, colormode=2)
  File "/usr/lib/pymodules/python2.7/matplotlib/backends/tkagg.py", line 13, in blit
    tk.call("PyAggImagePhoto", photoimage, id(aggimage), colormode, id(bbox_array))
RuntimeError: main thread is not in main loop
thread[thread-per-block[1]: <block image_sink1 (2)>]: caught unrecognized exception

The custom block (perform plotting) is written in Python, as below:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import numpy
from gnuradio import gr
from matplotlib import image, pyplot

class image_sink1(gr.sync_block):

    def __init__(self):

        gr.sync_block.__init__( self, name="image_sink1",
            in_sig=[ numpy.complex64 ],
            out_sig=None)
           
        pyplot.figure()
        pyplot.ion()
        pyplot.show()

        self.axes1 = pyplot.gca()
        #self.win   = self.axes1.figure.canvas.manager.window
        #self.win.after(100,animate)       
       
        self.completed = False
        self.img2 = numpy.zeros( (150,150,4), numpy.uint8 )
       
        self.coordinate = self.coordinate_stream()

    def coordinate_stream(self):
        for y in range(150):
            for x in range( 0, 150, 2 ):       
                yield y,x

    def work(self, input_items, output_items):       
        in0 = input_items[0]
       
        if self.completed:
            return -1
       
        for sample1 in in0:
            try:
                y,x = next( self.coordinate )

                if sample1.real > 0:
                    self.img2[y,x] = numpy.array([255,255,255,255])
                else:
                    self.img2[y,x] = numpy.array([0,0,0,255])
                       
                if sample1.imag > 0:
                    self.img2[y,x+1] = numpy.array([255,255,255,255])
                else:
                    self.img2[y,x+1] = numpy.array([0,0,0,255])
               
            except StopIteration:
                print "Receiver side completed!"
                self.complete = True           
           
        self.axes1.imshow( self.img2 )       
       
        self.axes1.figure.canvas.draw()   # or, pyplot.draw(), both gives error !!!
       
        return in0.size

Please advise,
thanks in advance.

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