Here is a gist that I thought would demonstrate the mangled images when running matplotlib + multiprocessing. However, it works fine when run with both.
#!/usr/bin/env python3
"""
This demonstrates that a bunch of images I create here look ruined when I run with multiprocessing, but look fine when run in parallel.
serial 100 images: run ./demonstration_borked_images.py -N 100
parallel 100 images: run ./demonstration_borked_images.py -N 100 -M
"""
import os, sys, numpy, glob, time
from multiprocessing import Pool, cpu_count
from matplotlib.backends.backend_agg import FigureCanvasAgg
from matplotlib.figure import Figure
from argparse import ArgumentParser
def create_demo_image( imageno ):
assert( isinstance( imageno, int ) )
assert( imageno >= 0 )
fig = Figure( figsize = ( 8 * 1.5, 6 * 1.5 ) )
ax = fig.add_subplot(111)
xyvals = numpy.random.random_sample( ( 300, 3 ) )
ax.scatter( xyvals[:,0], xyvals[:,1], c = xyvals[:,2], s = 20 )
ax.set_xlabel( 'X VALUES', fontsize = 14, fontweight = 'bold' )
ax.set_ylabel( 'Y VALUES', fontsize = 14, fontweight = 'bold' )
ax.set_title( 'IMAGE NUMBER %04d' % imageno )
canvas = FigureCanvasAgg(fig)
canvas.print_figure( 'figure_%04d.png' % imageno, bbox_inches = 'tight' )
if __name__ == '__main__':
parser = ArgumentParser( )
parser.add_argument( '-N', '--num', type=int, dest='num', action='store', default = 10,
help = 'Number of images to draw. Default is 10.' )
parser.add_argument( '-M', dest='do_multi', action='store_true', default = False,
help = ' '.join(
[
'If chosen, then create these images in parallel using multiprocessing.',
'Default is to create images in serial.' ]))
args = parser.parse_args( )
assert( args.num > 0 )
time0 = time.time( )
if not args.do_multi:
_ = list( map( create_demo_image, range( args.num ) ) )
else:
with Pool( processes = cpu_count( ) ) as pool:
_ = list( pool.map( create_demo_image, range( args.num ) ) )
#
## how long to run
print( 'took %0.3f seconds to process %02d images.' % (
time.time( ) - time0, args.num ) )