Problem of using threading with enigma

There are precautions about using threading with enigma and enigma experts advice to avoid using threading but if we follow some rules as experts said regarding using threading outside main thread we can use threading safely.

The following code demonstrates not real plugin to run simple counter thread just to simplify the problem.

although the counter runs well and can stop it at any moment but has problem in showing another screen if i want in opensource images and start enigma without error notification in dreamos enigma

what is the proper way to use the following simple thread?

from Screens.Screen import Screen
from Screens.MessageBox import MessageBox
from Components.ActionMap import NumberActionMap,ActionMap
from Components.Pixmap import Pixmap
from Components.Label import Label
from Plugins.Plugin import PluginDescriptor
import threading
import time


####

class Test(Screen):
	skin = """
		<screen name="myscreen" position="center,center" size="1000,700" title="Test thread" >
			<widget name="text" position="250,100" size="300,100" font="Regular;22" />			
                        <eLabel  position = "250,370"   zPosition = "4"   size = "300,25"  halign = "center"  font = "Regular;24"  transparent = "0" foregroundColor = "white" backgroundColor = "green" text = "start counter" />
			<eLabel  position = "250,470"   zPosition = "4"   size = "300,25"  halign = "center"  font = "Regular;24"  transparent = "0" foregroundColor = "white" backgroundColor = "red" text = "stop counter" />
			
		</screen>"""
	
	def __init__(self, session):

		Screen.__init__(self, session)
		
	        self['text']=Label('Press green to start counter ')
		self["actions"] = ActionMap(['ColorActions',"WizardActions" ],
		{			
			"back": self.close,
                        "green": self.startthread,                        
                        "red": self.stopcounter,
			"ok": self.close,
		}, -1)
               
                self.exitcounter=False
                
        def startthread(self):
                 
                self.active_thread = threading.Thread(target=self.startcounter, args=())
                self.active_thread.daemon = True
                self.active_thread.start()
                
        def startcounter(self):
          self['text'].setText('Counter started')
          i=0
          while i<60:
              i=i+1
              print str(i)
              time.sleep(1)
              
              self['text'].setText(str(i))
              if self.exitcounter:
                  self.exitcounter=False
                  
                  break
          self['text'].setText('Counter stopped')
            
        def stopcounter(self):
            self.exitcounter=True  

def main(session, **kwargs):
	session.open(Test)
	
def menu(menuid, **kwargs):
    if menuid == 'mainmenu':
        return [(_('testPlugin'),
          main,
          'testPlugin_mainmenu',
          1)]
    return []

def Plugins(**kwargs):
    list = []
    try:
        
            list.append(PluginDescriptor(icon='plugin.png', name='testPlugin', description='test enigma', where=PluginDescriptor.WHERE_MENU, fnc=menu))
    except:
        list.append(PluginDescriptor(icon='plugin.png', name='testPlugin', description='test enigma', where=PluginDescriptor.WHERE_MENU, fnc=menu))

    list.append(PluginDescriptor(icon='plugin.png', name='testPlugin', description='test enigma', where=PluginDescriptor.WHERE_PLUGINMENU, fnc=main))
    return list