MAX_FD = 5
FILENAME = __file__

import threading
import os
import random
import resource
import time

resource.setrlimit(resource.RLIMIT_NOFILE, (MAX_FD, MAX_FD))

fds = []

def run_in_thread():
    while True:
        try:
            fd = os.open(FILENAME, os.O_RDONLY)
            fds.append(fd)
        except OSError as exc:
            print(f"os.open failed: {exc!r}")
            break
    print(f"FDs open by the thread: {len(fds)} (max FD: {max(fds)})")
    for fd in range(MAX_FD):
        try:
            os.fstat(fd)
            valid = True
        except OSError:
            valid = False
        print(f"fd {fd} valid? {valid}")

print("spawn thread")
t = threading.Thread(target=run_in_thread)
t.start()
t.join()
for fd in fds:
    os.close(fd)
print("exit process")