How to prevent multiple initialization of dynamic library

Question

I am working on Python version 2.7. I have a module extension for Python written in C. The module initialization function PyMODINIT_FUNC initmymodule contains some code for initializing OpenSSL library. My module built as shared library and loading via imp.load_dynamic

This module may loading many times and I can't control it. Django and python doing that. And when it loading twice then OPENSSL_config function calling twice too. And it leading to process crash.

I can't control it from C-code, I can't control it from Python-code.

Here look at the docs http://docs.python.org/2.7/library/imp.html It says:

imp.load_dynamic Load and initialize a module implemented as a dynamically loadable shared library and return its module object. If the module was already initialized, it will be initialized again.

Nice.

I found that the similar problem was solved in Python version 3.4 http://hg.python.org/cpython/file/ad51ed93377c/Python/import.c#l459

Modules which do support multiple initialization set their m_size field to a non-negative number (indicating the size of the module-specific state). They are still recorded in the extensions dictionary, to avoid loading shared libraries twice.

But what shall I do in Python 2.7?

Answer 1

Maybe to do workaround by registering own custom import hook where you could control the case which causes you problem (prevent double initialization). Some references for writing custom import hooks:

• Python import hooks article
• PEP-302 New Import Hooks - python 2.3+
• create and register custom import/reload functions - example of implementation in project lazy_reload

This is hackish solution, so I suggest extra caution if this is to be used in production systems.