这些线程是否并行运行

Question

I have the following code:

from threading import Thread
from threading import currentThread


def f(i, name="default"):
    print("Thread named {} with id={} is working".format(name, i))


for i in range(3):
    Thread(target=f, args=(i,), kwargs={"name": "%s" % currentThread().getName()}).start()

This is the result that I get:

>> Thread named MainThread with id=0 is working
>> Thread named MainThread with id=1 is working
>> Thread named MainThread with id=2 is working

if these three threads are running in parallel why they all have the same name, if they are not running in parallel how can I change my code to make them run in parallel?

Answer 1

The value of the argument kwargs={"name": "%s" % currentThread().getName()} is evaluated at the same time as (or more precisely, just before) Thread is called. So each thread gets the keyword argument name="MainThread" passed to the function it is supposed to execute.

Try calling currentThread() inside f , for example:

def f(i):
    print("Thread named {} with id={} is working".format(currentThread().getName(), i)

Answer 2

if these three threads are running in parallel why they all have the same name

This is because your currentThread().getName() is being called in the thread spawning them, so it is passing the name of that thread to all the spawned ones.

if they are not running in parallel how can I change my code to make them run in parallel?

They are running in separate threads, but due to the behaviour of CPython, they are running the Python bytecode on the same processor, thus not fully concurrently. In order to make them run on separate processors, use the Multiprocessing module.