Python `io.open` intermittently throw `PermissionError` on windows

Bug report

Bug description:

The io.open method intermittently raises a PermissionError on the Windows operating system. I've attached a Python script that reproduces this issue on version 3.12.8, and 3.11.9 (didn't test for any other version)

My investigation suggests that the problem arises from consecutive write operations performed within very short timeframes where each operation does fresh io.open to write updates -- For example, when attempting to write 10 updates back-to-back to a file with fresh io.open each time.

On Windows, explorer.exe runs in the background to update indexing and metadata upon file modification. If explorer.exe has already acquired a handle to the file, any new request to write to it will result in a PermissionError.

While we could implement a retry mechanism with backoff for io.open in our code, I'm curious why Python doesn't natively handle such background process contention.

import time
import threading
import random
import multiprocessing
import os

# Sample message text
MESSAGE = (
    r"file://C:\Users\sample\Desktop\temp\tmpgzy8f_lt\929cec70297d4938b31545f858d6b38c.txt,"
    r"gs://sample-bucket/loadwintest/hdahsdhahdahsdhahd/temp/dahsdhahdhadhahdh/dhahsdahdhahdhahdahdhahdha.txt,"
    r"2025-07-21T10:44:43.263442Z,2025-07-21T11:00:55.588213Z,dahshdahdhahdhahshah+hfQ==,25000000000,25000000000,OK,"
)

# Output file path
output_file = "winman/test_output11.txt"


# Writer process – gets messages from queue and writes to file
def writer(queue, end_time):
    while time.time() < end_time:
        msg = queue.get()
        with open(output_file, "at", encoding='utf-8', newline='\n') as f:
            f.write(msg + '\n')


# Thread that puts messages into the queue
def thread_worker(queue, thread_id, process_id, end_time):
    while time.time() < end_time:
        notify_msg = f"[P{process_id}-T{thread_id}] {MESSAGE}"
        queue.put(notify_msg)
        time.sleep(random.choice([0.3, 0.5, 0.4]))


# Process that spawns multiple threads
def process_worker(queue, num_threads, process_id, end_time):
    threads = []
    for tid in range(num_threads):
        t = threading.Thread(target=thread_worker, args=(queue, tid, process_id, end_time))
        threads.append(t)
        t.start()

    for t in threads:
        t.join()


def main():
    runtime_seconds = 600
    end_time = time.time() + runtime_seconds

    num_processes = 4
    threads_per_process = 4

    queue = multiprocessing.Queue()

    # Start writer process
    writer_proc = multiprocessing.Process(target=writer, args=(queue, end_time))
    writer_proc.start()

    # Start worker processes
    processes = []
    for pid in range(num_processes):
        p = multiprocessing.Process(target=process_worker, args=(queue, threads_per_process, pid, end_time))
        p.start()
        processes.append(p)

    # Wait for all worker processes
    for p in processes:
        p.join()

    # Terminate writer after work is done
    writer_proc.terminate()
    writer_proc.join()


if __name__ == "__main__":
    main()

CPython versions tested on:

3.12

Operating systems tested on:

Windows

まず、報告された CPython バージョンを使って、添付された Python 再現プログラムを Windows 上で実行し、断続的な PermissionError を再現できるか確認してください。次に、io.open のエントリポイントと、Windows での関連するファイルオープン動作を調査してください。この作業では、再現可能な原因と、明確に範囲を定めた修正または文書化された制限を明らかにする必要があります。