python多处理和多线程的简单区别

import multiprocessing
import time
zero = 0
def change_zero():    
global zero    
for i in range(3):        
zero = zero + 1        
print(multiprocessing.current_process().name, zero)
if __name__ == '__main__':    
p1 = multiprocessing.Process(target = change_zero)    
p2 = multiprocessing.Process(target = change_zero)    
p1.start()    
p2.start()    
p1.join()    
p2.join()    
print(zero)