Python Multiprocessing

In this tutorial we will learn about the multiprocessing in python with some cool and easy examples.

Multiprocessing

Multiprocessing refers to the ability of a system to support more than one processor at the same time. Applications in a multiprocessing system are broken to smaller routines that run independently. The operating system allocates these threads to the processors improving performance of the system.

A multiprocessing system can have:

• multiprocessor, i.e. a computer with more than one central processor.
• multi-core processor, i.e. a single computing component with two or more independent actual processing units.

# importing the multiprocessing module 
import multiprocessing 
  
def print_cube(num): 
    """ 
    function to print cube of given num 
    """
    print("Cube: {}".format(num * num * num)) 
  
def print_square(num): 
    """ 
    function to print square of given num 
    """
    print("Square: {}".format(num * num)) 
  
if __name__ == "__main__": 
    # creating processes 
    p1 = multiprocessing.Process(target=print_square, args=(10, )) 
    p2 = multiprocessing.Process(target=print_cube, args=(10, )) 
  
    # starting process 1 
    p1.start() 
    # starting process 2 
    p2.start() 
  
    # wait until process 1 is finished 
    p1.join() 
    # wait until process 2 is finished 
    p2.join() 
  
    # both processes finished 
    print("Done!")

Let us try to understand the above code:

• To import the multiprocessing module, we do:

  import multiprocessing
  

• To create a process, we create an object of Process class. It takes following arguments:
  • target: the function to be executed by process
  • args: the arguments to be passed to the target function

  Note: Process constructor takes many other arguments also which will be discussed later. In above example, we created 2 processes with different target functions:

  p1 = multiprocessing.Process(target=print_square, args=(10, ))
  p2 = multiprocessing.Process(target=print_cube, args=(10, ))

  • To start a process, we use start method of Process class.

    p1.start()
    p2.start()
    

  • Once the processes start, the current program also keeps on executing. In order to stop execution of current program until a process is complete, we use join method.

    p1.join()
    p2.join()
    

    As a result, the current program will first wait for the completion of p1 and then p2. Once, they are completed, the next statements of current program are executed.

output:

Square: 100

Cube: 1000

Done!