How can I prevent pallon deallocating ctypes callbacks during exit?

Suppose I have the following shared library to download ctypes

. It allows you to register a callback to be called when the program exits or when you call it yourself:

#include <stdlib.h>
static void (*callback)(void);

void invoke_callback(void)
{
    callback();
}

void set_callback(void (*new_callback)(void))
{
    callback = new_callback;
}

void init(void)
{
    atexit(invoke_callback);
}

      

        
        
        
      

    

Then suppose I load this library using magic ctypes

:

import ctypes
shared = ctypes.CDLL('./test.so')

#a callback function
def callback():
    print "callback invoked"

#register functions to run at exit
shared.init()
#set the callback function to invoke
shared.set_callback(ctypes.CFUNCTYPE(None)(callback))
#invoke the callback function
shared.invoke_callback()

#...callback also invoked here, right?

      

        
        
        
      

    

I expected the output of this to be something like this:

callback invoked
callback invoked

      

        
        
        
      

    

Unfortunately for me it looked something like this:

callback invoked
Segmentation fault

      

        
        
        
      

    

Why is this, you ask? Well, it would seem that by the time the functions appeared, the atexit

python interpreter had previously de-allocated the memory containing the callbacks:

(gdb) backtrace
#0  0x000000000049b11d in ?? () <- uh-oh
#1  0x000000000046d245 in ?? () <- ctypes' wrapper?
#2  0x00007ffff6b554a9 in ?? () <- ctypes
   from /usr/lib/python2.7/lib-dynload/_ctypes.x86_64-linux-gnu.so
#3  0x00007ffff6944baf in ffi_closure_unix64_inner ()
   from /usr/lib/x86_64-linux-gnu/libffi.so.6
#4  0x00007ffff6944f28 in ffi_closure_unix64 ()
   from /usr/lib/x86_64-linux-gnu/libffi.so.6
#5  0x00007ffff673e71d in invoke_callback () at test.c:6 <- me
#6  0x00007ffff6f2abc9 in __run_exit_handlers (status=0, 
    listp=0x7ffff72965a8 <__exit_funcs>, 
    run_list_atexit=run_list_atexit@entry=true) at exit.c:82
#7  0x00007ffff6f2ac15 in __GI_exit (status=<optimized out>) at exit.c:104
#8  0x00007ffff6f14b4c in __libc_start_main (main=0x497d80 <main>, argc=2, 
    argv=0x7fffffffe408, init=<optimized out>, fini=<optimized out>, 
    rtld_fini=<optimized out>, stack_end=0x7fffffffe3f8) at libc-start.c:321
#9  0x0000000000497ca0 in _start ()

      

        
        
        
      

    

Now, my question. I am actually trying to tie into a fairly large C codebase (which I cannot change) containing multiple callbacks called during exit. They currently cause segmentation faults when the test program exits the system. Can this be prevented?