Python object 中的 C++ 对象包装器未销毁

Question

I noticed that C++ objects wrapped in Python object were not destroyed when the Python object was released.

Here is my type definition using CPython C API:

typedef struct {
    PyObject_HEAD
    CppFoo fooObj;
    std::vector<Py_ssize_t> size;
} FooObject;

And this is the tp_dealloc:

void FooObject_dealloc(FooObject* self) {
    Py_TYPE(self)->tp_free((PyObject*)self);
}

The FooObject_dealloc is hit in the debugger when following code is called in Python:

>>>myfoo=Foo()
>>>del myfoo

However, the destructor of CppFoo was not called even though the constructor was called in tp_init. How could this happen? Shouldn't the destructor of CppFoo called automatically when myfoo is released? What should be done to avoid the leak of fooObj?

EDIT: I pretty much followed the tutorial in the creation of the type:

https://docs.python.org/3/extending/newtypes_tutorial.html

The difference is that I added C++ objects to the type other than int or PyObject* after PyObject_HEAD.

Answer 1

In C++, construction of objects using dynamic memory involves two steps:

1. Allocate memory for the object(s).
2. Initialize the object(s) using a valid constructor.

On the other side, destruction of objects using dynamic memory also involves two steps:

1. Call the destructor to destruct the object(s).
2. Deallocate the memory for the object(s).

It's unclear from your post how you are constructing the object but the problem with the destruction is clear. You have code for step 2 but not for step 1.

I don't want to suggest a concrete way to correctly deal with destruction of the object until I see your code for constructing the object.