[PyQt] thread in pyqt ... simple example needed

[Hazen Babcock]

Arnold Krille wrote:
> On Sunday 05 April 2009 21:29:44 Hazen Babcock wrote:
>> I'd suggest expanding your MyThread class to something like this:
>> class MyThread(QtCore.QThread):
>>      def __init__(self, parent = None):
>>          QtCore.QThread.__init__(self, parent)
>>          self.running = 1
>>       def run(self):
>>           n = 0
>>           step = 1
>>           while self.running:
>>               n += step
>>               print n
>>               self.msleep(100)
>>      def stop(self):
>> 	 self.running = 0
>> You should also look at the QtCore.QMutex() class, which provides a way
>> to synchronize (via locking) between the thread process and other
>> processes.
> 
> Another reason while this will not work as expected is the Big Intepreter 
> Lock. Unless QThread releases the BIL in its *sleep-functions, the thread will 
> block the execution of the main-thread...
> 
> Arnold

Yeah that wasn't such a good suggestion. I actually tested this one and 
it works as expected for me:

import sys
from PyQt4 import QtCore, QtGui
import time

class MyThread(QtCore.QThread):
     def __init__(self, parent = None):
         QtCore.QThread.__init__(self, parent)
         self.alive = 1
         self.running = 0
         self.n = 0

     def run(self):
         while self.alive:
             step = 1
             n = 0
             while self.running:
                 n += step
                 print n
                 self.msleep(100)
             self.msleep(100)

     def toggle(self):
         if self.running:
             self.running = 0
         else:
             self.running = 1

     def stop(self):
         self.alive = 0

class Gui(QtGui.QWidget):
     def __init__(self, parent=None):
         QtGui.QGroupBox.__init__(self, parent)
         self.gcenter = QtGui.QPushButton("X", self)
         self.gcenter.setAutoRepeat(True)
         guiLayout = QtGui.QGridLayout()
         guiLayout.addWidget(self.gcenter,1,0)
         self.setLayout(guiLayout)
         self.thread = MyThread()
         self.thread.start()
         self.connect(self.gcenter, QtCore.SIGNAL("clicked()"), 
self.thread.toggle)


if __name__ == "__main__":
     app = QtGui.QApplication(sys.argv)
     gui = Gui()
     gui.show()
     sys.exit(app.exec_())


I assume that QThread must be releasing the GIL while sleeping.

-Hazen