not thread-safe function can break a django application?

[Fabio C. Barrionuevo da Luz]

I was trying to answer a question in a Brazilian forum about django.

one of the proposed solutions utilized the function locale.setlocale() from locale module.

according to the documentation[1] locale.setlocale() function is not thread-safe

the question is: 

not thread-safe function can break a django application?

If so, how?

Which scenario I would have problems?

some easily reproducible example of problems using not thread-safe function?

[1] https://docs.python.org/2/library/locale.html#locale.setlocale

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Fábio C. Barrionuevo da Luz
Acadêmico de Sistemas de Informação na Faculdade Católica do Tocantins - FACTO
Palmas - Tocantins - Brasil - América do Sul

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[Collin Anderson]

On Saturday, November 22, 2014 4:46:56 AM UTC-5, Fabio Caritas Barrionuevo da Luz wrote:

I was trying to answer a question in a Brazilian forum about django.

one of the proposed solutions utilized the function locale.setlocale() from locale module.

according to the documentation[1] locale.setlocale() function is not thread-safe

the question is: 

not thread-safe function can break a django application?

 Yes

If so, how? 

You can have "race conditions" where _sometimes_ you get unpredictable results.

Which scenario I would have problems? 

One request in one thread could set locale to English and then use the locale, meanwhile, another thread could set it to Spanish and then use the locale. If they did that at the same time, the English request might get the Spanish locale, or the Spanish request might get the English locale.

some easily reproducible example of problems using not thread-safe function?

import threading
state = {}

def english():
    state['locale'] = 'english'
    assert state['locale'] == 'english'

def spanish():
    state['locale'] = 'spanish'
    assert state['locale'] == 'spanish'

while 1:
    threading.Thread(target=english).start()
    threading.Thread(target=spanish).start()

 

(press ctrl+c to stop)

Also, note that it says "If the locale is not changed thereafter, using multithreading should not cause problems." So, if you only set it once and never change it, you should be fine.

Collin

[Fabio Caritas Barrionuevo da Luz]

Collin, Thanks for the explanation.