# To enable running multiple programs at the same time
import threading
# To enable flushing standard out. (That is, printing right away)
import sys
# To enable yeilding to other methods
import time
# To enable unlimited counting
import itertools

# How often to print for each of the methods
COUNT_STEP_SIZE = 10000000
PRIMES_STEP_SIZE = 10000

#
# Exercise instructions:
#
#  1. Run this program.  Obeserve what it does.  Do you have the patience to 
#     wait for "primes" to start? (Please don't feel compelled!)
#
#  2. In main, switch the order of the calls to count and primes.
#     Observe what it does.
#
#  3. To run both programs at the same time, we can use threads.
#     Create a thread to run the "primes" method using
#      primes_thread = threading.Thread(target=xxxx,args=yyyy)
#       where xxx is the name of the method you want to run (just the name!)
#       and yyyy is a tuple of the arguments you want to pass
#     
#     Start your thread using:
#      primes_thread.start()
#
#     Observe what happens.
#
#  4. In python, threads do not often yield to each other. To explictly yield t
#     another thread, you can use 
#      time.sleep(0) 
#
#     Observe what happens.
#     How much slower/faster do the programs run when threading?
#      
#  5. If you have time, you can adjust the parameters.  
#     How fairly are you able to share the processor? 

# Run two long programs
def main():
   print "Starting main"
   sys.stdout.flush()
   primes(PRIMES_STEP_SIZE)
   count(COUNT_STEP_SIZE) 

# Count up, printing current value occassionally
def count(step):
   print "Starting count"
   sys.stdout.flush()
   for i in itertools.count():
      if i%step==0:
         print "count: "+str(i)
         sys.stdout.flush()

# Find primes, printing a prime occassionally
def primes(step):
   print "Starting primes"
   sys.stdout.flush()
   doPrintNext = True
   for i in itertools.count():
      if i % step == 0: 
         doPrintNext = True
      isPrime = True;
      for j in xrange(2,i-1):
         if i%j == 0:
            isPrime = False;
            break;
      if isPrime and doPrintNext:
         print "prime: "+str(i)
         doPrintNext = False
         sys.stdout.flush()

if __name__ == "__main__":
   main()