How to exit from a function called my `multiprocessing.Pool`

Here is an example of the code I am using, when I put a condition to exit from function `worker` when I use this as a script in terminal it halts and does not exit. 

```
def worker(n):
    if n == 4:
        exit("wrong number")  # tried to use sys.exit(1) did not work
    return n*2

def caller(mylist, n=1):
    n_cores = n if n > 1 else multiprocessing.cpu_count()
    print(n_cores)
    pool = multiprocessing.Pool(processes=n_cores)
    result = pool.map(worker, mylist)
    pool.close()
    pool.join()
    return result

l = [2, 3, 60, 4]
myresult = caller(l, 4)

```