Interprocess communication with pyzmq and multiprocessing

pycuda_req_rep_demo.py

#!/usr/bin/env python

"""
Pass data between processes started through the multiprocessing module
using pyzmq and process them with PyCUDA
"""

import numpy as np
import zmq
import multiprocessing as mp

gpu = 0

def worker():
    import pycuda.driver as drv
    import pycuda.gpuarray as gpuarray
    import atexit

    # Initialize device:
    drv.init()
    dev = drv.Device(gpu)
    ctx = dev.make_context()
    atexit.register(ctx.pop)
    
    print dev.name()
       
    context = zmq.Context()
    socket = context.socket(zmq.REP)
    socket.connect("tcp://localhost:5555")

    # Process data sent to worker until a quit signal is transmitted:
    while True:
        data = socket.recv_pyobj()
        print "Worker %i: %s" % (gpu, data)
        if data == 'quit':
            break

        # Do something with the data on the GPU:
        data_gpu = gpuarray.to_gpu(data)
        result_gpu = -data_gpu

        socket.send_pyobj(result_gpu.get())

def master():

    # Data to send to worker:
    data_list = map(lambda x: np.random.rand(4, 4), xrange(4))

    context = zmq.Context()
    socket = context.socket(zmq.REQ)
    socket.bind("tcp://*:5555")

    # Send data out for processing and get back the results:
    for i in xrange(len(data_list)):
        socket.send_pyobj(data_list[i])
        result = socket.recv_pyobj()
        print "Master: ", result
    socket.send_pyobj('quit') 

if __name__ == '__main__':    
    worker = mp.Process(target=worker)
    worker.start()

    master()

Does this work if master() is called before starting the worker?

I've faced this issue, with python multiprocessing where if the publisher is started from the main thread before starting the subscriber (which is run in another process as you show), then the subscriber does not receive any messages. However, if I start the publisher in another process (it's important that the zmq.bind be done in the new process), then things work as expected, i.e the publisher can start before the subscriber.