call-pool.py

import requests
from requests.adapters import HTTPAdapter
import threading
import logging

logging.basicConfig(level=logging.DEBUG)

s = requests.session()

def call(url):
    s.get(url)


s.mount("https://", HTTPAdapter(pool_connections=1, pool_maxsize=2))

t0 = threading.Thread(target=call, args=("https://api.github.com", ))
t1 = threading.Thread(target=call, args=("https://api.github.com", ))

t0.start()
t1.start()

t0.join()
t1.join()

t2 = threading.Thread(target=call, args=("https://api.github.com", ))
t3 = threading.Thread(target=call, args=("https://api.github.com", ))

t2.start()
t3.start()

t2.join()
t3.join()