How to avoid gcc warning in Python C extension when using Py_BEGIN_ALLOW_THREADS

Question

The simplest way to manipulate the GIL in Python C extensions is to use the macros provided: ``` my_awesome_C_function() { blah; Py_BEGIN_ALLOW_THREADS // do stuff that doesn't need the GIL if (should_i_call_back) { Py_BLOCK_THREADS // do stuff that needs the GIL Py_UNBLOCK_THREADS } Py_END_ALLOW_THREADS return blah blah; } ``` This works great, letting me release the GIL for the bulk of my code, but re-grabbing it for small bits of code that need it. The problem is when I compile this with gcc, I get: ``` ext/engine.c:548: warning: '_save' might be used uninitialized in this function ``` because Py_BEGIN_ALLOW_THREADS is defined like this: ``` #define Py_BEGIN_ALLOW_THREADS { \ PyThreadState *_save; \ _save = PyEval_SaveThread(); ``` So, three questions: - Is it possible to suppress gcc's warning, - Does anyone have any idea why gcc thinks `_save` might be used uninitialized, since it is assigned to immediately after its declaration, and - Why wouldn't the macro have been defined to…

Accepted Answer

- Yes, it is possible to suppress uninitialized warnings using the -Wno- prefix.

`-Wall -Wno-uninitialized`

If you want to remove just this warning, you could simply initialize `_save` to a null pointer so that it doesn't rely on a function return value... that one line of code and a comment makes sense to me:

```
PyThreadState *_save; 
_save = 0; /* init as null pointer value */
_save = PyEval_SaveThread();
```

How to avoid gcc warning in Python C extension when using Py_BEGIN_ALLOW_THREADS

Solution

Problem