# PrimeCounter.py

# Python has multi-threading, but that doesn't take advantage of multiple cores because
# of an underlying global interpreter lock (GIL)

# multiprocessing is heavier (a new process is created). 

# the code below generates the correct answer for the threaded code, but only one processor is used
# It does run multiple processes if we use multithreading, but getCount returns 0 at the end. I think
# we would need to use a multiprocessing.Array to get information back to the main process.

# In order to make it possible to return a value to the main code with multiprocessing, I needed to use 
# the Value class, so this code is not really set up to work for both threading and multiprocessing.

# from threading import Thread as Worker
from multiprocessing import Process as Worker
from multiprocessing import Value
import time

class PrimeCounter(Worker):
    
    def __init__ (self, s, e, chunk_stride, chunk_size, shared_count):
        super().__init__() 
        self.begin = s
        self.extent = e
        self.chunk_stride = chunk_stride
        self.chunk_size = chunk_size
        self.count = 0
        self.shared_count = shared_count # this one is visible after the process is over. 

    def is_prime (self, n):
        if (n < 2):
            return False
        if (n == 2):
            return True
        if (n % 2 == 0):
            return False
        for i in range (3, n, 2):
            if (n % i == 0):
                return False;
        return True                    
        
    def run (self):
        print( "running thread with pid", self.pid )
        for offset in range( self.begin, self.begin + self.extent, self.chunk_stride ):
            for i in range (offset, offset+self.chunk_size):
                if self.is_prime(i):
                    self.count += 1      
        #print( "found",self.count,"primes", self.getCount() )
        self.shared_count.value = self.count
        return 0       
    
    def getCount (self):
        return self.count
        

def main ():
    N = 100000
    #N = 100
    count1 = Value('i')
    count2 = Value('i')
    count0 = Value('i')
    
    pc1 = PrimeCounter(0, N, 200, 100, count1)
    pc2 = PrimeCounter(100, N, 200, 100, count2)
    pc3 = PrimeCounter(0, N, N, N, count0)
   

    t1 = time.time()
    
    pc1.start()
    pc2.start()
       
    pc1.join()
    pc2.join()
    
    t2 = time.time()
    
    # need to use Value's to get the value from the process
    print("2 thread count ", count1.value + count2.value, " primes")
    print("time is ", t2 - t1)
    
    t1 = time.time()
    
    pc3.start()
    pc3.join()
    
    t2 = time.time()
    
    print("1 thread count ", count0.value, " primes")
    print("time is ", t2 - t1)
    
    
if __name__ == "__main__":
    main()