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                        #!/usr/bin/python
#encoding: utf-8
import sys
import time
import socket
import asyncore
import exceptions
from socket import AF_INET, SOCK_STREAM
from asyncore import dispatcher
from threading import Thread, RLock
class PiCalcThread(Thread):
    def __init__(self, buffer, lock):
        Thread.__init__(self)
        self.buffer = buffer
        self.lock = lock
        
    def run(self):
        """ See http://web.comlab.ox.ac.uk/oucl/work/jeremy.gibbons/publications/spigot.pdf """
        q,r,t,k,n,l = 1,0,1,1,3,3
        
        while True:
            if 4*q+r-t < n*t:
                self.lock.acquire()
                self.buffer.newDigits(str(n))
                self.lock.release()
                
                q,r,t,k,n,l = (10*q,10*(r-n*t),t,k,(10*(3*q+r))/t-10*n,l)
            else:
                q,r,t,k,n,l = (q*k,(2*q+r)*l,t*l,k+1,(q*(7*k+2)+r*l)/(t*l),l+2)
            
            time.sleep(0.001)
class PiGenerator(list):
    def __init__(self):
        list.__init__(self)
        self.calculator = None
        self.lock = RLock()
        self.digits = ''
    
    def subscribe(self, obj):  
        self.lock.acquire()
        try:     
            self.append(obj)
            self._notify(obj=obj)
        finally:
            self.lock.release()            
            
        if not self.calculator:
            self.calculator = PiCalcThread(self, self.lock)
            self.calculator.start()
        else:
            if len(self) > 0:
                self._resumeCalculator()
                
    def unsubscribe(self, obj):
        self.lock.acquire()
        self.remove(obj)   
        self.lock.release()
             
        if len(self) <= 0:
            self._pauseCalulator()
            
    def _pauseCalulator(self):
        self.lock.acquire()
    
    def _resumeCalculator(self):
        try: self.lock.release()
        except exceptions.AssertionError: pass
            
    def _notify(self, digits = None, obj = None):
        objs = [obj] if obj else self
        digits = digits or self.digits
        
        for obj in objs:
            obj.update(digits)
        
    def newDigits(self, digits):
        self.digits += digits
        self._notify(digits)