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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