Requests: gevent + requests blocks when using socks

I use python(2.7.6),gevnet(1.1.2),requests(2.11.1) to make http requests concurrent, and it works good. But when I add socks proxy to requests, it blocks.

This is my code:

import time
import requests
import logging
import click

import gevent
from gevent import monkey
monkey.patch_all()

FORMAT = '%(asctime)-15s %(message)s'
logging.basicConfig(format=FORMAT)
logger = logging.getLogger('test')

#socks proxy
user = MY_SOCKS_PROXY_USERNAME
password = MY_SOCKS_PROXY_PASSWORD
host = MY_SOCKS_PROXY_HOST
port = MY_SOCKS_PROXY_PORT
proxies = {
        'http': 'socks5://{0}:{1}@{2}:{3}'.format(user, password, host, port),
        'https': 'socks5://{0}:{1}@{2}:{3}'.format(user, password, host, port),
}
url = 'https://www.youtube.com/user/NBA'


def fetch_url(i,with_proxy):
    while True:
        logger.warning('thread %s fetch url'%i)
        try:
            if with_proxy:
                res = requests.get(url,proxies=proxies, timeout=5)
            else:
                res = requests.get(url, timeout=5)
        except Exception as e:
            logger.error(str(e))
            continue

        logger.warning(res.status_code)

def do_other_thing():
    while True:
        logger.warning('do other thing...')
        time.sleep(1)

@click.command()
@click.option('--with_proxy/--without_proxy',help='if use proxy', default=True)
def run(with_proxy):
    if with_proxy:
        logger.warning('with proxy......')
    else:
        logger.warning('without proxy......')
    ts = []
    ts.append(gevent.spawn(do_other_thing))
    for i in xrange(3):
        ts.append(gevent.spawn(fetch_url,i,with_proxy))
    gevent.joinall(ts)

if __name__=='__main__':
    run()

These pictures show the result.

run with proxy
run without proxy

With proxy, do_other_thing will blocks before fetch_url done.
Without proxy， it works good. (timeout error occurs, because of the GFW)

Can anyone help me solving this problem? Thanks very much!