Make 2 functions run at the same time

Question

I am trying to make 2 functions run at the same time.

def func1():
    print 'Working'

def func2():
    print 'Working'

func1()
func2()

Does anyone know how to do this?

Solution 1

Do this:

from threading import Thread

def func1():
    print('Working')

def func2():
    print("Working")

if __name__ == '__main__':
    Thread(target = func1).start()
    Thread(target = func2).start()

Solution 2

The answer about threading is good, but you need to be a bit more specific about what you want to do.

If you have two functions that both use a lot of CPU, threading (in CPython) will probably get you nowhere. Then you might want to have a look at the multiprocessing module or possibly you might want to use jython/IronPython.

If CPU-bound performance is the reason, you could even implement things in (non-threaded) C and get a much bigger speedup than doing two parallel things in python.

Without more information, it isn't easy to come up with a good answer.

Solution 3

This can be done elegantly with Ray, a system that allows you to easily parallelize and distribute your Python code.

To parallelize your example, you'd need to define your functions with the @ray.remote decorator, and then invoke them with .remote.

import ray

ray.init()

# Define functions you want to execute in parallel using 
# the ray.remote decorator.
@ray.remote
def func1():
    print("Working")

@ray.remote
def func2():
    print("Working")

# Execute func1 and func2 in parallel.
ray.get([func1.remote(), func2.remote()])

If func1() and func2() return results, you need to rewrite the above code a bit, by replacing ray.get([func1.remote(), func2.remote()]) with:

ret_id1 = func1.remote()
ret_id2 = func1.remote()
ret1, ret2 = ray.get([ret_id1, ret_id2])

There are a number of advantages of using Ray over the multiprocessing module or using multithreading. In particular, the same code will run on a single machine as well as on a cluster of machines.

For more advantages of Ray see this related post.

Solution 4

One option, that looks like it makes two functions run at the same
time, is using the threading module (example in this answer).

However, it has a small delay, as an Official Python Documentation
page describes. A better module to try using is multiprocessing.

Also, there's other Python modules that can be used for asynchronous execution (two pieces of code working at the same time). For some information about them and help to choose one, you can read this Stack Overflow question.

Comment from another user about the threading module

He might want to know that because of the Global Interpreter Lock
they will not execute at the exact same time even if the machine in
question has multiple CPUs. wiki.python.org/moin/GlobalInterpreterLock

– Jonas Elfström Jun 2 '10 at 11:39

Quote from the Documentation about threading module not working

CPython implementation detail: In CPython, due to the Global Interpreter
Lock, only one thread can execute Python code at once (even though
certain performance-oriented libraries might overcome this limitation).

If you want your application to make better use of the computational resources of multi-core machines, you are advised to use multiprocessing or concurrent.futures.ProcessPoolExecutor.
However, threading is still an appropriate model if you
want to run multiple I/O-bound tasks simultaneously.

Solution 5

The thread module does work simultaneously unlike multiprocess, but the timing is a bit off. The code below prints a "1" and a "2". These are called by different functions respectively. I did notice that when printed to the console, they would have slightly different timings.

from threading import Thread

def one():
    while(1 == num):
        print("1")
        time.sleep(2)
    
def two():
    while(1 == num):
        print("2")
        time.sleep(2)


p1 = Thread(target = one)
p2 = Thread(target = two)

p1.start()
p2.start()

Output: (Note the space is for the wait in between printing)

1
2

2
1

12
   
21

12
   
1
2

Not sure if there is a way to correct this, or if it matters at all. Just something I noticed.

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