Race condition

race.py

# The following almost immediately raises an assertion error under nogil
# Under cpython it completes all 1000 iterations no problem

from threading import Thread
import time

positions = []


def race(n):
    # Race to be the first worker thread to complete!
    time.sleep(0.1)
    positions.append(n)
    # Assert that we're the last thing in the array
    assert len(positions) == positions.index(n) + 1


def go():
    positions.clear()

    ts = [Thread(target=race, args=(n,)) for n in range(8)]
    for t in ts:
        t.start()
    for t in ts:
        t.join()


for k in range(1000):
    if k % 100 == 0:
        print(f"=== {k} tries ===")
    go()