Memory leaks in MFC dialog base application when use scoped_interpreter

[ruoleng]

The example code in VC 2017 give a leak tip in debug mode.
Output windows show text like this:

Detected memory leaks!
Dumping objects ->
{266} normal block at 0x00C9B4E8, 4 bytes long.
Data: < > 00 00 00 00
Object dump complete.

I had try the code in Win32 Application, it's OK, no leak.

The version of Visual Stuido 2017 I'm using is 15.9.16.

It seem the "internals_pp" pointer did not release.
In "internals.h" file of function "inline internals **&get_internals_pp() ".

Reproducible example code

namespace py = pybind11;
py::scoped_interpreter guard{};
auto dtPassTo = py::dict();
auto global = py::dict(py::module::import("main").attr("dict"));
dtPassTo["msg"] = py::cpp_function(
[](std::string strMsg) {
::MessageBoxA(nullptr, strMsg.c_str(), "", MB_OK);
});

py::exec("msg('test')", global, dtPassTo);

[ruoleng]

Well, I did a little dig. Then I found in 'internals.h' file, the function 'PYBIND11_NOINLINE inline internals &get_internals() ' there is a code block (line 272 ~ 274 ):

    if (!internals_pp) internals_pp = new internals*();
    auto *&internals_ptr = *internals_pp;
    internals_ptr = new internals();

Find out internals_pp is a pointer that point to another pointer. But only release the *internals_pp pointer, not release the internals_pp pointer.
The release code in line 163 ~ 166 in the embed.h file, which is the block of function ‘inline void finalize_interpreter() '.

After I add release internals_pp pointer , there is not more leak.

Before fix, release code is :

if (*internals_ptr_ptr) {
delete *internals_ptr_ptr;
*internals_ptr_ptr = nullptr;
}

After fix , release code is :

if (*internals_ptr_ptr) {
delete *internals_ptr_ptr;
*internals_ptr_ptr = nullptr;
}

if (internals_ptr_ptr) {
delete internals_ptr_ptr;
internals_ptr_ptr = nullptr;
}

Sorry, for my poor English. I wish that make you clear the leak.

[erwincoumans]

I can confirm there is a memory leak, even without MFC.
In my case, 'finalize_interpreter' in embed.h doesn't seem to be called. Where/how is finalize_interpreter called?

pybind11/include/pybind11/detail/internals.h

Line 272 in 4f72ef8

if (!internals_pp) internals_pp = new internals*();

[bstaletic]

We know about this. Help is needed.

#2024

[bstaletic]

@rwgk fixed this one in #2413.