Pipe inheritance broken on Windows since 3.13

Bug report

Bug description:

Passing an inheritable pipe file descriptor to a child process is somehow broken on Windows since Python 3.13. Opening the file descriptor in the child process crashes with [WinError 6] the handle is invalid.

> py -3.12-64 .\main.py
INFO:root:S: Starting
INFO:root:Duration for 10000 requests: 0.37447249999968335 s
INFO:root:S: EOF Quitting
> py -3.13-64 .\main.py
INFO:root:S: Starting
Traceback (most recent call last):
  File "D:\temp\test-pipe-main\sub.py", line 31, in <module>
    main()
    ~~~~^^
  File "D:\temp\test-pipe-main\sub.py", line 14, in main
    reply_write_fobj = os.fdopen(reply_write_fd, "wb", buffering=0)
  File "<frozen os>", line 1068, in fdopen
OSError: [WinError 6] Das Handle ist ungültig

Minimal example

import logging
import os
import pickle
import sys
import time


def main():
    logging.basicConfig(level=logging.INFO)
    reply_read_fd, reply_write_fd = os.pipe()
    request_read_fd, request_write_fd = os.pipe()
    child_fds = [reply_write_fd, request_read_fd]
    for fd in child_fds:
        os.set_inheritable(fd, True)

    reply_read_fobj = os.fdopen(reply_read_fd, "rb", buffering=0)
    request_write_fobj = os.fdopen(request_write_fd, "wb", buffering=0)

    child_pid = os.spawnl(
        os.P_NOWAIT,
        sys.executable,
        os.path.basename(sys.executable),
        "sub.py",
        *(str(fd) for fd in child_fds),
    )
    for fd in child_fds:
        os.close(fd)

    number_requests = 10000
    start = time.perf_counter()
    for i in range(number_requests):
        request = f"test{i}"
        pickle.dump(request, request_write_fobj)
        logging.debug(f"C: Sent {request}")
        reply = pickle.load(reply_read_fobj)
        logging.debug(f"C: Got {reply}")

    duration = time.perf_counter() - start
    logging.info(f"Duration for {number_requests} requests: {duration} s")
    request_write_fobj.close()
    os.waitpid(child_pid, 0)
    time.sleep(1)


if __name__ == "__main__":
    main()

import logging
import os
import pickle
import sys


def main():
    logging.basicConfig(level=logging.INFO)
    reply_write_fd = int(sys.argv[1])
    request_read_fd = int(sys.argv[2])

    logging.info("S: Starting")

    reply_write_fobj = os.fdopen(reply_write_fd, "wb", buffering=0)
    request_read_fobj = os.fdopen(request_read_fd, "rb", buffering=0)
    logging.debug("S: Sent event")
    while True:
        try:
            request: str = pickle.load(request_read_fobj)
        except EOFError:
            logging.info("S: EOF Quitting")
            return
        logging.debug(f"S: Handle {request}")
        reply = "test"
        pickle.dump(reply, reply_write_fobj)

        logging.debug("S: Sent event")


if __name__ == "__main__":
    main()

CPython versions tested on:

3.12, 3.13

Operating systems tested on:

Windows

Commencez par exécuter main.py et sub.py fournis sous Windows avec Python 3.12 et 3.13, en vous concentrant sur os.pipe, os.set_inheritable, os.spawnl et os.fdopen. Suivez le chemin du processus Windows et de l’héritage du tube afin d’identifier pourquoi le processus enfant reçoit un handle invalide, puis vérifiez la correction avec un test de régression couvrant l’exemple minimal.