Threading a lengthy C function

Thomas Heller theller at
Thu Nov 20 18:24:53 CET 2003

sdd <daniels at> writes:

> Leo Breebaart wrote:
>> ...
>> If, however, I use the kind of run() method that I *really* need:
>>     def run(self):
>>       retvalue = mypackage.sleep(50)
>> where mypackage.sleep() is in fact a SWIG-generated wrapper
>> around the C library sleep() function the entire application
>> will *still* lock up completely until this task is done.
> As you suspect, this is the GIL at work.

I always wondered why (apparently) SWIG does not release the lock before
calling into C code and acquire it back afterwards.

If the original posters intent is simply to call functions in a dll, he
should probably try out ctypes - ctypes handles the GIL automatically
(release before calling the function, acquire it back after return of
the function, and even grabbing the GIL if a callback into Python is
done).  And it avoids SWIG completely.


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