[Python-Dev] Dealing with import lock deadlock in Import Hooks

Arnaud Fontaine arnaud.fontaine at nexedi.com
Tue Aug 13 10:28:42 CEST 2013

Antoine Pitrou <solipsis at pitrou.net> writes:
> On Tue, 13 Aug 2013 11:06:51 +0900 Arnaud Fontaine <arnaud.fontaine at nexedi.com> wrote:
>> I suggested the same in my initial email, but I was wondering if there
>> could be any issue by releasing the lock in find_module()/load_module()
>> until the module is actually added to sys.modules.
> Well, you are obviously on your own with such hacks. There is a reason
> the lock exists.

Yes. Actually, I was thinking about implementing something similar to
what has been done in Python 3.3 but for Python 2.7 with a corser-grain
lock. From my understanding of import.c, it should work but I was hoping
that someone with more experience in import code would confirm:

  Currently, I have a package, foo, registered into sys.meta_path which
  loads modules through its find_module() and load_module() methods

  Access to load_module() of this package is protected by a RLock I
  defined, so that modules within foo cannot be imported in
  parallel. Until the module is added to sys.modules and then the code
  loaded, release the import lock.

  For find_module(), only filter the full module name and if this is a
  module from foo package, then acquired the same RLock defined for
  load_module() to access variables shared with find_module().

Also, if a patch backporting the features from Python 3.3 to import.c
for Python 2.7 would be written, is there any chance it could be

Arnaud Fontaine

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