python ctypes 垃圾回收

Question

我正在使用 ctypes 从 python 访问 c 库(它实际上是 c++ 代码):

class CRMeAnnotationList(object):
def __init__(self):
    self.obj = lib.CRMeAnnotationList_new()de
def __del__(self):
    if self.obj:
        lib.CRMeAnnotationList_destroy(self.obj)
lst = CRMeAnnotationList()

C 代码如下所示

extern "C" {__declspec(dllexport) CRMeAnnotationList* CRMeAnnotationList_new() 
                { return new CRMeAnnotationList(); 
                }
            __declspec(dllexport)void CRMeAnnotationList_destroy(CRMeAnnotationList* p)
                {
                if (p)
                    delete p;
                }
            }

这段代码给了我 完成，退出代码 -1073741819 (0xC0000005)

而如果我不销毁指针，我会得到 0 作为退出代码。

这是否意味着我不需要销毁该指针，即执行 python 代码中的析构函数部分 del ？

Answer 1

您可能正在运行 64 位 Python，并且尚未正确设置 .argtypes 和 .restype。

示例:

测试.cpp

#define API __declspec(dllexport) // Windows-specific

extern "C" {

struct CRMeAnnotationList {
    int a;
};

API CRMeAnnotationList* CRMeAnnotationList_new() {
    return new CRMeAnnotationList();
}

API void CRMeAnnotationList_destroy(CRMeAnnotationList* p) {
    if(p)
        delete p;
}

}

测试.py

from ctypes import *

lib = CDLL('test')
lib.CRMeAnnotationList_new.argtypes = None
lib.CRMeAnnotationList_new.restype = c_void_p
lib.CRMeAnnotationList_destroy.argtypes = c_void_p,
lib.CRMeAnnotationList_destroy.restype = None

class CRMeAnnotationList:

    def __init__(self):
        print(f'created   {id(self):#x}')
        self.obj = lib.CRMeAnnotationList_new()

    def __del__(self):
        print(f'destroyed {id(self):#x}')
        if self.obj:
            lib.CRMeAnnotationList_destroy(self.obj)

lst = CRMeAnnotationList()

输出:

created   0x2232dfc35c0
destroyed 0x2232dfc35c0

当 .argtypes 和 .restype 行被注释掉时的输出:

created   0x1c98e8f35c0
destroyed 0x1c98e8f35c0
Exception ignored in: <function CRMeAnnotationList.__del__ at 0x000001C98E9176A8>
Traceback (most recent call last):
  File "C:\Users\metolone\Desktop\test.py", line 16, in __del__
OSError: exception: access violation reading 0xFFFFFFFF8C6CABCF

记下访问冲突的地址。它是一个 32 位值，符号扩展为 64 位。