[PyQt] Multiprocessing and ProgressBar

[Nicola Creati]

Hello,
I'm trying to develop a simple application that should do some 
calculation in a multiprocessing process and update a progress bar. I 
have tried to use the signal-slot technology to update the progress bar 
but at the end of my computation the gui crashes and i get:

python: ../../src/xcb_io.c:242: process_responses: Assertion `(((long) 
(dpy->last_request_read) - (long) (dpy->request)) <= 0)' failed.

Thi sis the code i'm using:

#--------------------------------------------------------------------------------------------
import sys, time
from multiprocessing import Process
import PyQt4.QtCore as QtCore
import PyQt4.QtGui as QtGui


class Compute(object):
    def __init__(self, win):
        self.win = win
   
    def calculate(self):
        for i in range (100):
            self.progressBar(i)
            time.sleep(0.05)
   
    def progressBar(self, value):
        self.win.updatePb.emit(value)
       
#-------------------------------------------------------------------------------
class Form(QtGui.QDialog):
   
  updatePb = QtCore.pyqtSignal(int)
 
  def __init__(self, parent=None):
    super(Form, self).__init__(parent)
   
    self.progressBar = QtGui.QProgressBar()
    self.progressBar.setMinimum(0)
    self.progressBar.setMaximum(100)
    self.progressBar.setValue(0)
    bbox = QtGui.QDialogButtonBox()
    bbox.setOrientation(QtCore.Qt.Horizontal)
    bbox.setStandardButtons(QtGui.QDialogButtonBox.Ok)
    layout = QtGui.QVBoxLayout(self)
    layout.addWidget(self.progressBar)
    layout.addWidget(bbox)
    bbox.clicked.connect(self.calculate)
   
    self.updatePb.connect(self.progressBar.setValue)
        
  def calculate(self):
    co = Compute(self)
    p = Process(target=co.calculate)
    p.start()
    p.join()


Thanks.

Nicola