Can I explicitly close a ctypes CDLL?

Question

I have a Python 2.7 GUI for interacting with a C library. I do a bunch of setup in the GUI, then I press \"go\" button. Then, I\'m looking at results and no longer need the libr

Answer 1

You need to close the handle to the DLL so it released first so you can work with the file, you need to get the handle of the library and then pass it to FreeLibrary on Windows, then you can do what you need with the DLL file:

from ctypes import *

file = CDLL('file.dll')

# do stuff here

handle = file._handle # obtain the DLL handle

windll.kernel32.FreeLibrary(handle)

preview:

Here is a test DLL:

#include <windows.h>
#include <stdio.h>

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) {

  switch( fdwReason ) {
    case DLL_PROCESS_ATTACH:
      puts("DLL loaded");
    break;

    case DLL_PROCESS_DETACH:
      puts("DLL unloaded");
    break;

    case DLL_THREAD_ATTACH:
    break;

    case DLL_THREAD_DETACH:
    break;
  }

  return TRUE;
}

__declspec(dllexport) void function(void) {
  puts("Hello");
}

preview:

>>> from ctypes import *
>>>
>>> file = CDLL('file.dll')
DLL loaded
>>>
>>> # now it's locked
...
>>> file.function()
Hello
0
>>> windll.kernel32.FreeLibrary(file._handle)
DLL unloaded
1
>>> # not it's unlocked

on Linux you use dlclose it would be:

from ctypes import *

file = CDLL('./file.so')

# do stuff here

handle = file._handle # obtain the SO handle

cdll.LoadLibrary('libdl.so').dlclose(handle)

Here is a similar shared object:

#include <stdio.h>

__attribute__((constructor)) void dlentry(void) {
  puts("SO loaded");
}

void function(void) {
  puts("Hello");
}

__attribute__((destructor)) void dlexit(void) {
  puts("SO unloaded");
}

preview:

>>> from ctypes import *
>>> 
>>> file = CDLL('./file.so')
SO loaded
>>> 
>>> file.function()
Hello
6
>>> cdll.LoadLibrary('libdl.so').dlclose(file._handle)
SO unloaded
0
>>>