Pyqtgraph multiprocessing coordination example

pyqt_mp_test.py

import queue
from pyqtgraph.Qt import QtGui, QtCore
import numpy as np
import pyqtgraph as pg
import multiprocessing
import time


# This function is responsible for displaying the data
# it is run in its own process to liberate main process
def display(name, q, e, q_empty):
    app = QtGui.QApplication([])

    win2 = pg.GraphicsWindow(title="Basic plotting examples")
    win2.resize(1000, 600)
    win2.setWindowTitle('pyqtgraph example: Plotting')
    p2 = win2.addPlot(title="Updating plot")
    curve = p2.plot(pen='y')

    x_np = []
    y_np = []

    def updateInProc(curve, q, x, y):
        # check stop event
        if e.is_set():
            item = q.get()
            x.append(item[0])
            y.append(item[1])
            curve.setData(x, y)
        else:
            i = 0
            print("[DISPLAY] Emptying queue.")
            while True:
                try:
                    q.get(block=False)
                    i += 1
                except queue.Empty:
                    print("[DISPLAY] Items that were left in queue: ", i)
                    q_empty.set()
                    break
            print("[DISPLAY] App quitting.")
            QtGui.QApplication.closeAllWindows()

    timer = QtCore.QTimer()
    timer.timeout.connect(lambda: updateInProc(curve, q, x_np, y_np))
    timer.start()

    app.exec_()
    print("[DISPLAY] Exec returned.")


# This is function is responsible for reading some data (IO, serial port, etc)
# and forwarding it to the display
# it is run in a thread
def producer(running, q, q_empty):
    t = 0
    while True:
        if running.is_set():
            s = np.sin(2 * np.pi * t)
            t += 0.01
            q.put([t, s])
            time.sleep(0.0001)
        else:
            print(
                "[PRODUCER] Done putting on queue. Waiting for q_empty event.")
            q_empty.wait()
            print("[PRODUCER] Queue was emptied.")
            break


if __name__ == '__main__':
    ctx = multiprocessing.get_context("spawn")
    q = ctx.Queue()
    # Event for stopping the IO thread
    run = ctx.Event()
    run.set()
    q_empty = ctx.Event()
    # Run io function in a thread
    t = ctx.Process(target=producer, args=(run, q, q_empty))
    # Start display process
    p = ctx.Process(target=display, args=('bob', q, run, q_empty))
    t.daemon = False
    p.daemon = False
    t.start()
    p.start()
    input("Type any key to quit.\n")
    run.clear()
    print("Waiting for graph window process to join...")
    p.join()
    print("Waiting for scheduler thread to join...")
    t.join()
    print("Process joined successfully.")