Embedding Python in a C extension

[kai028]

Thanks for the reply. I'm looking into the Global Interpreter Lock
today.

On Thu, 03 Jun 2010 01:07:39 +0100, MRAB <python at mrabarnett.plus.com>
wrote:

>Paul at mail.python.org wrote:
>> I have a problem with embedding Python into a C extension in Windows
>> Vista. I have implemented a timer routine in C as an extension, which
>> I can import into Python 2.6.5 and run. Each timer interval, the
>> extension calls a C CALLBACK function. I want to be able to have this
>> CALLBACK function call a Python function, so that I can write the
>> timer handler in Python.
>> 
>> I can write Python functions and call them from a C extension function
>> with no trouble in all cases EXCEPT when the function that calls the
>> Python code is the timer's CALLBACK function. That is, if I call
>> PyRun_SimpleString or PyRun_SimpleFile, or PyImport_ImportModule, or
>> basically any Python-y function in the CALLBACK function, Python
>> crashes and I get a window saying "Python has stopped working. Windows
>> is searching for a solution to the problem."
>> 
>> The Python code runs fine if I call it from a function in the
>> extension that is not the CALLBACK function. And regular C code runs
>> in the CALLBACK function properly. It only crashes if I try to run the
>> Python code from the timer CALLBACK function (or any C function I call
>> from the CALLBACK function).
>> 
>> Does anybody know how to fix this? Is there a workaround of some sort?
>
>Here's a quote from the Python docs at:
>
>     http://docs.python.org/c-api/init.html
>
>"""The Python interpreter is not fully thread safe. In order to support
>multi-threaded Python programs, there's a global lock, called the global
>interpreter lock or GIL, that must be held by the current thread before
>it can safely access Python objects. Without the lock, even the simplest
>operations could cause problems in a multi-threaded program: for
>example, when two threads simultaneously increment the reference count
>of the same object, the reference count could end up being incremented
>only once instead of twice."""
>
>That's probably what's happening to you.