Posts Tagged threading

pycurl CurlMulti example

I needed a process to perform multiple web services calls and return the combined results. Efficiency was fairly important, so I needed an asynchronous solution. I had used pycurl previously, but not in this fashion, so CurlMulti was new to me. Now, I wouldn’t use pycurl where urllib/urllib2 or httplib will do, but this is just such a case. The reason I’m posting my code (modified to remove some inessential peculiarities) is that I had trouble finding a good example. The pycurl docs only give a trivial example of CurlMulti usage involving one handle (!) and no provision for marshaling response data. I briefly considered using urllib2 and threading, but I’d rather leave thread management to the experts.

import pycurl
from cStringIO import StringIO

urls = [...] # list of urls
# reqs: List of individual requests.
# Each list element will be a 3-tuple of url (string), response string buffer
# (cStringIO.StringIO), and request handle (pycurl.Curl object).
reqs = [] 

# Build multi-request object.
m = pycurl.CurlMulti()
for url in urls: 
    response = StringIO()
    handle = pycurl.Curl()
    handle.setopt(pycurl.URL, url)
    handle.setopt(pycurl.WRITEFUNCTION, response.write)
    req = (url, response, handle)
    # Note that the handle must be added to the multi object
    # by reference to the req tuple (threading?).
    m.add_handle(req[2])
    reqs.append(req)

# Perform multi-request.
# This code copied from pycurl docs, modified to explicitly
# set num_handles before the outer while loop.
SELECT_TIMEOUT = 1.0
num_handles = len(reqs)
while num_handles:
    ret = m.select(SELECT_TIMEOUT)
    if ret == -1:
        continue
    while 1:
        ret, num_handles = m.perform()
        if ret != pycurl.E_CALL_MULTI_PERFORM: 
            break

for req in reqs:
    # req[1].getvalue() contains response content
    ...
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