python / python/cpython

Does CPython >= 3.10, <=3.12 support a thread-safe increment?

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Description

Documentation

There is no information about it in docs. But the code demonstrates that increment works correctly in multithreading context.

import concurrent.futures


def inc():
    global count
    for _ in range(1000):
        count += 1

for threads_count in range(1, 101):
    for _ in range(3):
        count = 0
        with concurrent.futures.ThreadPoolExecutor(max_workers=threads_count) as exe:
            for _ in range(10000):
                exe.submit(inc)

        print(f"{threads_count=}, {count=}")


import dis
dis.dis(inc)
output

threads=1, count=10000000
threads=1, count=10000000
threads=1, count=10000000
threads=2, count=10000000
threads=2, count=10000000
threads=2, count=10000000
threads=3, count=10000000
threads=3, count=10000000
threads=3, count=10000000
threads=4, count=10000000
threads=4, count=10000000
threads=4, count=10000000
threads=5, count=10000000
threads=5, count=10000000
threads=5, count=10000000
threads=6, count=10000000
threads=6, count=10000000
threads=6, count=10000000
threads=7, count=10000000
threads=7, count=10000000
threads=7, count=10000000
threads=8, count=10000000
threads=8, count=10000000
threads=8, count=10000000
threads=9, count=10000000
threads=9, count=10000000
threads=9, count=10000000
threads=10, count=10000000
threads=10, count=10000000
threads=10, count=10000000
threads=11, count=10000000
threads=11, count=10000000
threads=11, count=10000000
threads=12, count=10000000
threads=12, count=10000000
threads=12, count=10000000
threads=13, count=10000000
threads=13, count=10000000
threads=13, count=10000000
threads=14, count=10000000
threads=14, count=10000000
threads=14, count=10000000
threads=15, count=10000000
threads=15, count=10000000
threads=15, count=10000000
threads=16, count=10000000
threads=16, count=10000000
threads=16, count=10000000
threads=17, count=10000000
threads=17, count=10000000
threads=17, count=10000000
threads=18, count=10000000
threads=18, count=10000000
threads=18, count=10000000
threads=19, count=10000000
threads=19, count=10000000
threads=19, count=10000000
threads=20, count=10000000
threads=20, count=10000000
threads=20, count=10000000
threads=21, count=10000000
threads=21, count=10000000
threads=21, count=10000000
threads=22, count=10000000
threads=22, count=10000000
threads=22, count=10000000
threads=23, count=10000000
threads=23, count=10000000
threads=23, count=10000000
threads=24, count=10000000
threads=24, count=10000000
threads=24, count=10000000
threads=25, count=10000000
threads=25, count=10000000
threads=25, count=10000000
threads=26, count=10000000
threads=26, count=10000000
threads=26, count=10000000
threads=27, count=10000000
threads=27, count=10000000
threads=27, count=10000000
threads=28, count=10000000
threads=28, count=10000000
threads=28, count=10000000
threads=29, count=10000000
threads=29, count=10000000
threads=29, count=10000000
threads=30, count=10000000
threads=30, count=10000000
threads=30, count=10000000
threads=31, count=10000000
threads=31, count=10000000
threads=31, count=10000000
threads=32, count=10000000
threads=32, count=10000000
threads=32, count=10000000
threads=33, count=10000000
threads=33, count=10000000
threads=33, count=10000000
threads=34, count=10000000
threads=34, count=10000000
threads=34, count=10000000
threads=35, count=10000000
threads=35, count=10000000
threads=35, count=10000000
threads=36, count=10000000
threads=36, count=10000000
threads=36, count=10000000
threads=37, count=10000000
threads=37, count=10000000
threads=37, count=10000000
threads=38, count=10000000
threads=38, count=10000000
threads=38, count=10000000
threads=39, count=10000000
threads=39, count=10000000
threads=39, count=10000000
threads=40, count=10000000
threads=40, count=10000000
threads=40, count=10000000
threads=41, count=10000000
threads=41, count=10000000
threads=41, count=10000000
threads=42, count=10000000
threads=42, count=10000000
threads=42, count=10000000
threads=43, count=10000000
threads=43, count=10000000
threads=43, count=10000000
threads=44, count=10000000
threads=44, count=10000000
threads=44, count=10000000
threads=45, count=10000000
threads=45, count=10000000
threads=45, count=10000000
threads=46, count=10000000
threads=46, count=10000000
threads=46, count=10000000
threads=47, count=10000000
threads=47, count=10000000
threads=47, count=10000000
threads=48, count=10000000
threads=48, count=10000000
threads=48, count=10000000
threads=49, count=10000000
threads=49, count=10000000
threads=49, count=10000000
threads=50, count=10000000
threads=50, count=10000000
threads=50, count=10000000
threads=51, count=10000000
threads=51, count=10000000
threads=51, count=10000000
threads=52, count=10000000
threads=52, count=10000000
threads=52, count=10000000
threads=53, count=10000000
threads=53, count=10000000
threads=53, count=10000000
threads=54, count=10000000
threads=54, count=10000000
threads=54, count=10000000
threads=55, count=10000000
threads=55, count=10000000
threads=55, count=10000000
threads=56, count=10000000
threads=56, count=10000000
threads=56, count=10000000
threads=57, count=10000000
threads=57, count=10000000
threads=57, count=10000000
threads=58, count=10000000
threads=58, count=10000000
threads=58, count=10000000
threads=59, count=10000000
threads=59, count=10000000
threads=59, count=10000000
threads=60, count=10000000
threads=60, count=10000000
threads=60, count=10000000
threads=61, count=10000000
threads=61, count=10000000
threads=61, count=10000000
threads=62, count=10000000
threads=62, count=10000000
threads=62, count=10000000
threads=63, count=10000000
threads=63, count=10000000
threads=63, count=10000000
threads=64, count=10000000
threads=64, count=10000000
threads=64, count=10000000
threads=65, count=10000000
threads=65, count=10000000
threads=65, count=10000000
threads=66, count=10000000
threads=66, count=10000000
threads=66, count=10000000
threads=67, count=10000000
threads=67, count=10000000
threads=67, count=10000000
threads=68, count=10000000
threads=68, count=10000000
threads=68, count=10000000
threads=69, count=10000000
threads=69, count=10000000
threads=69, count=10000000
threads=70, count=10000000
threads=70, count=10000000
threads=70, count=10000000
threads=71, count=10000000
threads=71, count=10000000
threads=71, count=10000000
threads=72, count=10000000
threads=72, count=10000000
threads=72, count=10000000
threads=73, count=10000000
threads=73, count=10000000
threads=73, count=10000000
threads=74, count=10000000
threads=74, count=10000000
threads=74, count=10000000
threads=75, count=10000000
threads=75, count=10000000
threads=75, count=10000000
threads=76, count=10000000
threads=76, count=10000000
threads=76, count=10000000
threads=77, count=10000000
threads=77, count=10000000
threads=77, count=10000000
threads=78, count=10000000
threads=78, count=10000000
threads=78, count=10000000
threads=79, count=10000000
threads=79, count=10000000
threads=79, count=10000000
threads=80, count=10000000
threads=80, count=10000000
threads=80, count=10000000
threads=81, count=10000000
threads=81, count=10000000
threads=81, count=10000000
threads=82, count=10000000
threads=82, count=10000000
threads=82, count=10000000
threads=83, count=10000000
threads=83, count=10000000
threads=83, count=10000000
threads=84, count=10000000
threads=84, count=10000000
threads=84, count=10000000
threads=85, count=10000000
threads=85, count=10000000
threads=85, count=10000000
threads=86, count=10000000
threads=86, count=10000000
threads=86, count=10000000
threads=87, count=10000000
threads=87, count=10000000
threads=87, count=10000000
threads=88, count=10000000
threads=88, count=10000000
threads=88, count=10000000
threads=89, count=10000000
threads=89, count=10000000
threads=89, count=10000000
threads=90, count=10000000
threads=90, count=10000000
threads=90, count=10000000
threads=91, count=10000000
threads=91, count=10000000
threads=91, count=10000000
threads=92, count=10000000
threads=92, count=10000000
threads=92, count=10000000
threads=93, count=10000000
threads=93, count=10000000
threads=93, count=10000000
threads=94, count=10000000
threads=94, count=10000000
threads=94, count=10000000
threads=95, count=10000000
threads=95, count=10000000
threads=95, count=10000000
threads=96, count=10000000
threads=96, count=10000000
threads=96, count=10000000
threads=97, count=10000000
threads=97, count=10000000
threads=97, count=10000000
threads=98, count=10000000
threads=98, count=10000000
threads=98, count=10000000
threads=99, count=10000000
threads=99, count=10000000
threads=99, count=10000000
threads=100, count=10000000
threads=100, count=10000000
threads=100, count=10000000
11 0 LOAD_GLOBAL 0 (range)
2 LOAD_CONST 1 (1000)
4 CALL_FUNCTION 1
6 GET_ITER
>> 8 FOR_ITER 6 (to 22)
10 STORE_FAST 0 (_)

12 12 LOAD_GLOBAL 1 (count)
14 LOAD_CONST 2 (1)
16 INPLACE_ADD
18 STORE_GLOBAL 1 (count)
20 JUMP_ABSOLUTE 4 (to 8)

11 >> 22 LOAD_CONST 0 (None)
24 RETURN_VALUE

Looks like '+=' isn't an atomic op. But stiil I have a correct result.

Can we just use it as a guarantee or it is just an accent coincidence?

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  3. Forkez le dépôt et travaillez sur une branche.
  4. Ouvrez une pull request qui référence le numéro de l'issue.

Piste de recherche

Commencez par l’exemple ThreadPoolExecutor signalé, la fonction inc et son désassemblage. Examinez la documentation existante sur le threading Python et la référence du langage afin de déterminer quelle garantie, le cas échéant, s’applique à travers CPython 3.10–3.12. Le travail est terminé lorsque le comportement propre à chaque version et la possibilité de se fier à += sont clairement documentés.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

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