Python - threads not executing concurrently, why?

[MyName13]

import threading, time

def timer():
    for x in range(5):
        time.sleep(1)
        print("x is: ", x)
        

def printer():
    print("printer")
 
    
t = threading.Thread(target = timer())
t2 = threading.Thread(target = printer())

t.start()
t2.start()

 

Why is thread 2 (t2) executing only after thread 1 (t) is done?Shouldn't they run concurrently?

 

 

[Zeko369]

from multiprocessing import Process
import time

def timer():
    for x in range(5):
        time.sleep(1)
        print("x is: ", x)

def printer():
    print("printer")

if __name__ == '__main__':
    Process(target=timer).start()
    Process(target=printer).start()

 

Try this

[MyName13]

51 minutes ago, Zeko369 said:

 

Try this

It's still working as before (not concurrently / in parallel).

 

I know that multiprocessing can run in parallel unlike threads, but I want to know why my threads aren't running concurrently.

 

EDIT:

Wait, my target has parentheses (target=printer()), it shouldn't have those and after removing them both threads run

[Zeko369]

8 minutes ago, MyName13 said:

It's still working as before (not concurrently / in parallel).

 

Works fine for me with this code

 

from multiprocessing import Process
import time

def timer():
    for x in range(5):
        time.sleep(1)
        print("x is: ", x)

def printer():
    while(1):
        print("printer")
        time.sleep(0.5)

if __name__ == '__main__':
    Process(target=timer).start()
    Process(target=printer).start()

 

[MyName13]

7 minutes ago, Zeko369 said:

 

Works fine for me with this code

 

from multiprocessing import Process
import time

def timer():
    for x in range(5):
        time.sleep(1)
        print("x is: ", x)

def printer():
    while(1):
        print("printer")
        time.sleep(0.5)

if __name__ == '__main__':
    Process(target=timer).start()
    Process(target=printer).start()

 

I put parentheses in the target, threading version works now, but multiprocessing doesn't (nothing happens).

 

EDIT: interesting, it doesn't work in IDLE but works in CMD it also doesn't work without if name == main (in IDLE nothing is displayed, but in CMD lots of errors are printed out).

[mathijs727]

5 minutes ago, MyName13 said:

I put parentheses in the target, threading version works now, but multiprocessing doesn't (nothing happens).

 

EDIT: interesting, it doesn't work in IDLE but works in CMD it also doesn't work without if name == main (in IDLE nothing is displayed, but in CMD lots of errors are printed out).

Without the name==main it will recursively call itself IIRC

[MyName13]

Just now, mathijs727 said:

Without the name==main it will recursively call itself IIRC

What will call itself?Programs can work without that line too (you can simply write Main() instead of that).

[mathijs727]

14 minutes ago, MyName13 said:

What will call itself?Programs can work without that line too (you can simply write Main() instead of that).

Programs can work without the line which is actually what causes the problem.

When you start a new process you create a new instance of the Python interpreter which interprets the source file and then runs the function.

This means that anything that is not within name==main will be executed.

If you dont use name==main then it would also execute the line that creates a new process, creating a recursion.

 

On my install Python will recognize the problem and throw an error instead of getting into an endless recursion.

However, when using multiprocessing Pool object with map_async it does recurse and crash without the main call:

from multiprocessing import Pool

def inc(x):
	return x+1

p = Pool()
result = p.map_async(inc, [1,2,3,4,5])
print(result.get())

 

[mathijs727]

EDIT: ignore this post. Post notifications on iOS are buggy