I’m trying to synchronize multiple threads. I expect script output when using threading.Condition and threading.Barrier will be about the same, but it’s not. Please explain why this is happening.

In general, I need threads to perform work (some IO operation) in an infinite loop, but each cycle starts with the permission of the master thread, and permission is given only after the previous cycle is completed by all threads.

script 1

from threading import Barrier, Thread
from time import sleep, time

br = Barrier(3)
store = []

def f1():
    while True:
        br.wait()
        sleep(1)
        print("Calc part1")

def f2():
    while True:
        br.wait()
        sleep(1)
        print("Calc part2")


Thread(target=f1).start()
Thread(target=f2).start()

for i in range(10):
    br.wait()
    print(f'end iter {i}')
    print(f'-------------')

expected behavior

ent iter 0
-------------
Calc part1
Calc part2
ent iter 1
-------------
Calc part1
Calc part2
ent iter 2
-------------
Calc part1
Calc part2
ent iter 3
-------------
Calc part1

script 2

from threading import Condition, Thread
from time import sleep

condition = False
cv = Condition()

def predicate():
    return condition

def f1():
    for i in range(3):
        with cv:
            cv.wait_for(predicate)
            sleep(1)
            print("Calc part1")

def f2():
    for i in range(3):
        with cv:
            cv.wait_for(predicate)
            sleep(1)
            print("Calc part2")


Thread(target=f1).start()
Thread(target=f2).start()

with cv:
    condition = True
    cv.notify_all()

unexpected behavior

Calc part1
Calc part1
Calc part1
Calc part2
Calc part2
Calc part2

Why stdout of threads not mixed in result of second script?