import sys
import time

import pymongo
from pymongo import MongoClient
from pymongo.errors import PyMongoError
from threading import Thread

client = MongoClient("mongodb://localhost:27017/")
coll1 = client.test1.test1
coll2 = client.test1.test1
N_SLOW_FINDS = 20


coll1.insert_one({})
coll2.insert_one({})
mdb_version = client.server_info()["version"]
print(f"MongoDB: {mdb_version}, PyMongo: {pymongo.__version__}, Python: {sys.version}")

def slow_find():
    coll1.find_one({"$where": "sleep(5000) || true"}, comment="FIND_SLOW")

def fast_find():
    start = time.monotonic()
    try:
        # coll1.database.list_collection_names()
        coll2.find_one({"_id": 1}, comment="FIND_FAST")
    except PyMongoError as exc:
        print(f"FIND_FAST failed after {time.monotonic()-start} seconds: {exc}")
    else:
        print(f"FIND_FAST succeeded after {time.monotonic() - start} seconds")

# Run fast find once to get a baseline.
fast_find()

print(f"Starting {N_SLOW_FINDS} slow find operations in parallel")
threads = [Thread(target=slow_find) for _ in range(N_SLOW_FINDS)]
for t in threads:
    t.start()

# Run fast find again to show that it blocks on the slow finds.
time.sleep(0.5)  # Sleep to ensure the above finds have started.
fast_find()

for t in threads:
    t.join()

$ python3 repro-find-hang-where.py
MongoDB: 7.0.16, PyMongo: 4.12.0.dev0, Python: 3.13.0 (v3.13.0:60403a5409f, Oct  7 2024, 00:37:40) [Clang 15.0.0 (clang-1500.3.9.4)]
FIND_FAST succeeded after 0.000891833973582834 seconds
Starting 20 slow find operations in parallel
FIND_FAST succeeded after 4.556467916991096 seconds