Python Parallel Programming Video 12. Python process communication by using Queue.

Python multiprocessing communication
Exchanging object through the communication Channel
Process with Queue
Producer and consumer problem with queue

[muneshj]

Hi Mohit sir, which one of your book should I buy for python to learn more.

[bennguyen]

I'm trying to use multiprocessing's queue to send data, but it never seems to get the data. Any ideas?


File #1 (main.py):

from matplotlib_graph as mplive
from time import time, sleep
from multiprocessing import Queue as mpQueue

if __name__=='__main__':
try:
# Shared Memory
q = mpQueue()

# Start Plotter
mpInst = mplive.PlotClass( q )
mpInst.run()

# Push Data to Plotter
while True:
q.put(1)
sleep(1)

except KeyboardInterrupt:
print ("Keyboard Interrupt!")




File #2 (matplotlib_graph.py):

import matplotlib.pyplot as plt
import matplotlib.animation as animation
global ani # **Must be assigned to a global variable****

class PlotClass:
# Create *STATIC LOCAL* instances accessible across class functions
fig = None
ax = None
line1 = None
q = None
x_list_vec = []
y1_list_vec = []

def __init__(self, qdata ): __#Class__ Object __init__
# Save handle to Queue
self.q = qdata

# this is the call to matplotlib that allows dynamic plotting
plt.ion()

# Setup Figure with 'size' number of elements
self.fig = plt.figure(figsize=(13, 6))
self.ax = self.fig.add_subplot(111)

# Create a list variable to the animation
self.line1, = self.ax.plot(self.x_list_vec, self.y1_list_vec, marker = 'o', label='y1', color='r')

#Show a starting plot
plt.ion()
plt.xticks(rotation=45, ha='right')
plt.title('Title: Hello World')

plt.show()

def update(self, frame_num, user_arg1, user_arg2):
while self.q.empty() is False:
print ("Got Data!") #<<<< Never Executes!!!
print ( self.q.get() )

#Dummy Draw
self.line1.set_data(0, 6)

#Must return list when blit=True
return self.line1,

# Override the run function of Thread class
def run(self):
# **Must be assigned to a global variable!****
global ani
ani = animation.FuncAnimation(fig=self.fig, func=self.update, fargs=["Hi", 2], interval=0.1, blit=True, repeat=False)