Gevent pool with nested web requests

I try to organize pool with maximum 10 concurrent downloads. The function should download base url, then parser all urls on this page and download each of them, but OVERALL number of concurrent downloads should not exceed 10.

from lxml import etree 
import gevent
from gevent import monkey, pool
import requests

monkey.patch_all()
urls = [
    'http://www.google.com', 
    'http://www.yandex.ru', 
    'http://www.python.org', 
    'http://stackoverflow.com',
    # ... another 100 urls
    ]

LINKS_ON_PAGE=[]
POOL = pool.Pool(10)

def parse_urls(page):
    html = etree.HTML(page)
    if html:
        links = [link for link in html.xpath("//a/@href") if 'http' in link]
    # Download each url that appears in the main URL
    for link in links:
        data = requests.get(link)
        LINKS_ON_PAGE.append('%s: %s bytes: %r' % (link, len(data.content), data.status_code))

def get_base_urls(url):
    # Download the main URL
    data = requests.get(url)
    parse_urls(data.content)

How can I organize it to go concurrent way, but to keep the general global Pool limit for ALL web requests?

Bryan Mayes

I think the following should get you what you want. I'm using BeautifulSoup in my example instead the link striping stuff you had.

from bs4 import BeautifulSoup
import requests
import gevent
from gevent import monkey, pool
monkey.patch_all()

jobs = []
links = []
p = pool.Pool(10)

urls = [
    'http://www.google.com', 
    # ... another 100 urls
]

def get_links(url):
    r = requests.get(url)
    if r.status_code == 200:
        soup = BeautifulSoup(r.text)
        links + soup.find_all('a')

for url in urls:
    jobs.append(p.spawn(get_links, url))
gevent.joinall(jobs)

gevent.pool will limit the concurrent greenlets, not the connections.

You should use session with HTTPAdapter

connection_limit = 10
adapter = requests.adapters.HTTPAdapter(pool_connections=connection_limit, 
                                        pool_maxsize=connection_limit)
session = requests.session()
session.mount('http://', adapter)
session.get('some url')
# or do your work with gevent
from gevent.pool import Pool
# it should bigger than connection limit if the time of processing data 
# is longer than downings, 
# to give a change run processing.
pool_size = 15 
pool = Pool(pool_size)
for url in urls:
    pool.spawn(session.get, url)

You should use gevent.queue to do it in the right way.

Also this(eventlet examples) will be helpful for you to understand the basic idea.

Gevent solution is similar to the eventlet.

Keep in mind that will have somewhere to store visited URLs, so as not to get cycling, so you do not get out of memory error, you need to introduce some restrictions.

来源：https://stackoverflow.com/questions/15322701/gevent-pool-with-nested-web-requests

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