Python Threads and C Semaphores

[Andrew MacIntyre]

Dejan Rodiger wrote:
> Jeremy said the following on 16.1.2007 8:27:
>
>> I have a fat C++ extension to a Python 2.3.4 program. In all, I count
>> five threads. Of these, two are started in Python using
>> thread.start_new_thread(), and both of these wait on semaphores in the C++
>> extension using sem_wait(). There also are two other Python threads and one 
>> thread running wholly in
>> the extension.
>>
>> I notice that when one of the Python threads calls the extension and waits
>> on a semaphore, all but the C++ thread halt even when not waiting on any
>> semaphore. How do we get this working right?
> 
> Check the Global Interpreter Lock

More specifically, make sure that any extension code that does not
call Python API functions releases the GIL for the duration.

Look into the Py_BEGIN_ALLOW_THREADS/Py_END_ALLOW_THREADS macros and the
PyGILState*() API functions (these API functions appeared in Python 2.3).

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