Python child process silently crashes when issuing an HTTP request

Question

Python child process silently crashes when issuing an HTTP request

1.7k views Asked by Romain G At 10 June 2015 at 20:13

I'm running into an issue when combining multiprocessing, requests (or urllib2) and nltk. Here is a very simple code:

>>> from multiprocessing import Process
>>> import requests
>>> from pprint import pprint
>>> Process(target=lambda: pprint(
        requests.get('https://api.github.com'))).start()
>>> <Response [200]>  # this is the response displayed by the call to `pprint`.

A bit more details on what this piece of code does:

Import a few required modules
Start a child process
Issue an HTTP GET request to 'api.github.com' from the child process
Display the result

This is working great. The problem comes when importing nltk:

>>> import nltk
>>> Process(target=lambda: pprint(
        requests.get('https://api.github.com'))).start()
>>> # nothing happens!

After having imported NLTK, the requests actually silently crashes the thread (if you try with a named function instead of the lambda function, adding a few print statement before and after the call, you'll see that the execution stops right on the call to requests.get) Does anybody have any idea what in NLTK could explain such behavior, and how to get overcome the issue?

Here are the version I'm using:

$> python --version
Python 2.7.5
$> pip freeze | grep nltk
nltk==2.0.5
$> pip freeze | grep requests
requests==2.2.1

I'm running Mac OS X v. 10.9.5.

Thanks!

Original Q&A

There are 3 answers

Vikas Ojha On 10 June 2015 at 21:57

It seems using Nltk and Python Requests in a child process is rare. Try using Thread instead of Process, I was having exactly same issue with some other library and Requests and replacing Process with Thread worked for me.

Sasinda Rukshan On 12 October 2016 at 22:48

This issue still seems not solved. https://github.com/nltk/nltk/issues/947 I think this is a serious issue (unless you are playing with NLTK, doing POCs and trying out models, not actual apps) I am running the NLP pipelines in RQ workers (http://python-rq.org/)

nltk==3.2.1
requests==2.9.1

**alvas** · Accepted Answer · 2015-08-06 00:50:01

Updating your python libraries and python should resolve the problem:

alvas@ubi:~$ pip freeze | grep nltk
nltk==3.0.3
alvas@ubi:~$ pip freeze | grep requests
requests==2.7.0
alvas@ubi:~$ python --version
Python 2.7.6
alvas@ubi:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.2 LTS
Release:    14.04
Codename:   trusty

From code:

from multiprocessing import Process
import nltk
import time


def child_fn():
    print "Fetch URL"
    import urllib2
    print urllib2.urlopen("https://www.google.com").read()[:100]
    print "Done"


while True:
    child_process = Process(target=child_fn)
    child_process.start()
    child_process.join()
    print "Child process returned"
    time.sleep(1)

[out]:

Fetch URL
<!doctype html><html itemscope="" itemtype="http://schema.org/WebPage" lang="de"><head><meta content
Done
Child process returned
Fetch URL
<!doctype html><html itemscope="" itemtype="http://schema.org/WebPage" lang="de"><head><meta content
Done
Child process returned
Fetch URL
<!doctype html><html itemscope="" itemtype="http://schema.org/WebPage" lang="de"><head><meta content
Done
Child process returned

From code:

alvas@ubi:~$ python
Python 2.7.6 (default, Jun 22 2015, 17:58:13) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from multiprocessing import Process
>>> import requests
>>> from pprint import pprint
>>> Process(target=lambda: pprint(
...         requests.get('https://api.github.com'))).start()
>>> <Response [200]>

>>> import nltk
>>> Process(target=lambda: pprint(
...         requests.get('https://api.github.com'))).start()
>>> <Response [200]>

It should work with python3 too:

alvas@ubi:~$ python3
Python 3.4.0 (default, Jun 19 2015, 14:20:21) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from multiprocessing import Process
>>> import requests
>>> Process(target=lambda: print(requests.get('https://api.github.com'))).start()
>>> 
>>> <Response [200]>

>>> import nltk
>>> Process(target=lambda: print(requests.get('https://api.github.com'))).start()
>>> <Response [200]>

TechQA.

Python child process silently crashes when issuing an HTTP request

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