如何在使用Py_BEGIN_ALLOW_THREADS时避免Python C扩展中的gcc警告 [英] How to avoid gcc warning in Python C extension when using Py_BEGIN_ALLOW_THREADS

问题描述

在Python C扩展中操纵GIL的最简单方法是使用提供的宏：

  my_awesome_C_function（）
 {
 blah; 
 
 Py_BEGIN_ALLOW_THREADS 
 
 //做一些不需要GIL的东西
 
 if（should_i_call_back）{
 Py_BLOCK_THREADS 
 //做需要GIL的东西
 Py_UNBLOCK_THREADS 
} 
 
 Py_END_ALLOW_THREADS 
 
 return blah blah; 
} 
  

这很好，让我释放大部分代码的GIL，但重新获取它需要它的小部分代码。

问题是，当我用gcc编译这个时，我得到：

  ext / engine.c：548：warning：'_save'可能在此函数中未初始化使用
   
 
 
  #define Py_BEGIN_ALLOW_THREADS {pre 
 
 
 \ 
 PyThreadState * _save; \ 
 _save = PyEval_SaveThread（）; 
  
所以，有三个问题：
 
 
 
 
是否可以抑制gcc的警告，
 
 
有没有人知道为什么gcc认为可以使用 _save 未初始化，因为它在声明后立即分配，并且
 
为什么宏定义不能在一个语句中声明和初始化变量以避免该问题？
 > 
 
（后两个确实只是为了我自己的好奇心）。
 
 
我可以避免这个问题，不要使用宏，而是自己做，但我宁愿不要。
解决方案
 
 
 
是的，可以使用-Wno-前缀来抑制未初始化的警告。 
 
 
  -Wall -Wno-uninitialized  
 
 
 
如果您只想删除此警告，您可以简单地将 _save 初始化为空指针，以便它不依赖函数返回值...一行代码和一条评论对我来说很有意义：
  PyThreadState * _save; 
 _save = 0; / * init作为空指针值* / 
 _save = PyEval_SaveThread（）; 
  
 
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 declare and initialize the variable in one statement to avoid the issue?
(the last two are really just for my own curiosity).

I can avoid the issue by not using the macros and doing it all myself, but I'd rather not.
解决方案

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();


                        
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