File descriptor leak using multiprocessing.Queue

Bug report

Bug description:

"Too many open files" can occur with multiprocessing.Queue, even if the protocol used to work with the queue is correct.

The file descriptor leak can be demonstrated with two small programs:

File "ko.py"

import os
import multiprocessing

pid = os.getpid()
cmd = f'lsof -p {pid} | grep -i pipe | wc -l'
cmdfull = f'lsof -p {pid} | grep -i pipe'
queues = {}

for i in range(100):
    queues[i] = multiprocessing.Queue()
    os.system(cmd)
    queues[i].close()
    queues[i].join_thread()
    os.system(cmd)

os.system(cmdfull)

File "ok.py"

import os
import multiprocessing

pid = os.getpid()
cmd = f'lsof -p {pid} | grep -i pipe | wc -l'
cmdfull = f'lsof -p {pid} | grep -i pipe'
queues = {}

for i in range(100):
    queues[i] = multiprocessing.Queue()
    queues[i].put('Hello')
    os.system(cmd)
    queues[i].close()
    queues[i].join_thread()
    os.system(cmd)

os.system(cmdfull)

An empty queue that remains empty is not abnormal (e.g., an error queue when no errors occur).

The workaround is to create a class extending multiprocessing.Queue, adding a close method that inserts an extra message into the queue before performing the actual close.

This issue can be observed on Linux and macOS. However, it is not specific to a particular operating system.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Empieza ejecutando las reproducciones ko.py y ok.py en un sistema Linux o macOS compatible y compara sus recuentos de descriptores de archivo. Después inspecciona las rutas close y join_thread de multiprocessing.Queue; se considerará completado cuando cerrar repetidamente colas vacías ya no deje los descriptores mostrados por lsof y se conserve el comportamiento funcional demostrado por ok.py.