[Pythoncard-users] multithreading Pythoncard applications

[<kc1...@ya...>]

Somebody asked me for a sample program on how to
multithread a Pythoncard application.

Multithreading in Python is pretty easy to code.  All
you have to do is to declare a class that's
subclassing from the threading.thread class and then
kick start it with a start method.  Like:

import threading

class Worker(threading.Thread):
   def __init__(self):
      threading.Thread.__init__(self)

   def run(self):
   ....actual code...

myWorker=Worker().start()

The actual work, of course, is synchronization.  The
Thread class provides counters, locks, and so forth to
help that.

I've put together a very simple mind multi-thread
example to show how to do things in Pythoncard.  The
code doesn't quite work yet (I did it real quick over
lunch time) in that the thread doesn't release the CPU
like I expect it to and so one thread would hog the
CPU and doesn't switch between threads).  But for
those that are not familiar with multi-threading
PythonCard, this can serve as a sample.  

If you get the code to work properly, it should allow
the user to click the Start menu option twice, and it
would run 2 processing threads, and when the user
click on Stop, both threads would stop.

#!/usr/bin/python

"""
__version__ = "$Revision: 1.1 $"
__date__ = "$Date: 2004/10/24 19:21:46 $"
"""

import wx
import threading
import thread
import time

from PythonCard import model

class MyBackground(model.Background):

	def on_initialize(self, event):
		# if you have any initialization
		# including sizer setup, do it here
		self.running(False)
		self.textAreas=(self.components.TextArea1,)
		pass

	def on_menuFileStart_select(self, event):
		on_menuFileStart_exe(self.textAreas[0])
		return
	
	def on_menuFileStart_exe(self, textArea):
		textArea.visible=True
		self.running(True)
		for i in range(10000000):
			textArea.text = "Got up to %d" % i
			##            print i
			for j in range(i):
				k = 0
				time.sleep(0)
				if not self.running(): break
			try:
				wx.SafeYield(self)
			except:
				pass
			if not self.running(): break
		textArea.text = "Finished at %d" % i
		return
		
	def on_menuFileStop_select(self, event):
		self.running(False)

	def on_Stop_mouseClick(self, event):
		self.on_menuFileStop_select(event)
		pass

	def running(self, flag=None):
		if flag!=None:
			self.runningFlag=flag
		return self.runningFlag
		

class MyBackgroundThreaded(MyBackground):

	def on_initialize(self, event):
		# if you have any initialization
		# including sizer setup, do it here
		self.myLock=thread.allocate_lock()
		self.myThreadCount = 0
		self.running(False)
		self.textAreas=[self.components.TextArea1,]
		self.textAreas.append(self.components.TextArea2)
		pass

	def on_menuFileStart_select(self, event):
		self.myThread=MyBackgroundWorker(self).run()

	def on_menuFileStop_select(self, event):
		self.running(False)
		self.menuBar.setEnabled("menuFileStart", True)

	def on_Stop_mouseClick(self, event):
		self.on_menuFileStop_select(event)

	def running(self, flag=None):
		self.myLock.acquire()
		if flag!=None:
			self.runningFlag=flag
		flag=self.runningFlag
		self.myLock.release()
		return flag
		
class MyBackgroundWorker(threading.Thread):
	def __init__(self, parent):
		threading.Thread.__init__(self)
		self.parent=parent
		self.parent.myLock.acquire()
		threadCount=self.parent.myThreadCount
		self.parent.myLock.release()
		self.textArea=self.parent.textAreas[threadCount]
		
	def run(self):
		self.parent.myLock.acquire()
		self.parent.myThreadCount += 1
		if self.parent.myThreadCount==2:
			self.parent.menuBar.setEnabled("menuFileStart",
False)
		self.parent.myLock.release()
		
		self.parent.on_menuFileStart_exe(self.textArea)
		
		self.parent.myLock.acquire()
		self.parent.myThreadCount -= 1
		if self.parent.myThreadCount==0:
			self.parent.menuBar.setEnabled("menuFileStart",
True)
		self.parent.myLock.release()

		return
	
if __name__ == '__main__':
	app = model.Application(MyBackgroundThreaded)
	app.MainLoop()



Here's the resource file:

{'application':{'type':'Application',
          'name':'Template',
    'backgrounds': [
    {'type':'Background',
          'name':'bgTemplate',
          'title':'Standard Template with File->Exit
menu',
          'size':(400, 300),
          'style':['resizeable'],

        'menubar': {'type':'MenuBar',
         'menus': [
             {'type':'Menu',
             'name':'menuFile',
             'label':'&File',
             'items': [
                  {'type':'MenuItem',
                   'name':'menuFileStart',
                   'label':u'&Start',
                  },
                  {'type':'MenuItem',
                   'name':'menuFileStop',
                   'label':u'Sto&p',
                  },
                  {'type':'MenuItem',
                   'name':'menuFile--',
                   'label':u'--',
                  },
                  {'type':'MenuItem',
                   'name':'menuFileExit',
                   'label':'E&xit',
                   'command':'exit',
                  },
              ]
             },
         ]
     },
         'components': [

{'type':'StaticText', 
    'name':'TextArea1', 
    'position':(10, 100), 
    'text':u'This is a test', 
    'visible':False, 
    },

{'type':'StaticText', 
    'name':'TextArea2', 
    'position':(10, 200), 
    'text':u'This is a test', 
    'visible':False, 
    },

] # end components
} # end background
] # end backgrounds
} }




--
John Henry