Loading a DLL many times with WinDLL under Python

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When using the ctypes library in Python to load a DLL multiple times using WinDLL, it's important to understand the implications and potential issues that might arise. Loading the same DLL multiple times might not always work as expected due to how DLL loading and reference counting work in Windows. Here are some points to consider:

  1. Reference Counting:
    When you use WinDLL to load a DLL, Python maintains a reference count for that loaded DLL. Each time you use WinDLL to load the same DLL, the reference count is increased. This means that the DLL will only be unloaded when its reference count drops to zero (i.e., when you explicitly call .__del__() on the WinDLL object or when the script exits).

  2. Re-entrant Behavior:
    DLLs are not inherently designed to be loaded multiple times within the same process. Loading a DLL multiple times can lead to unexpected behavior, memory leaks, or crashes. DLLs are usually designed to be loaded once and then shared among different parts of the program.

  3. Side Effects:
    If the DLL contains global state or initialization code that should run only once, loading it multiple times might cause issues. Subsequent calls to the DLL might not have the expected behavior.

  4. Resource Management:
    If the DLL allocates resources (memory, handles, etc.), you need to ensure proper cleanup and deallocation to avoid resource leaks.

If you need to access functions from the same DLL multiple times, it's generally better to load the DLL once and use that instance throughout your program. If you need separate instances for some reason, you should design your DLL to support that behavior properly.

However, if you still want to load the same DLL multiple times, you might consider using cdll instead of WinDLL. cdll loads the DLL using the LoadLibrary function, which might be more suitable for this purpose. But keep in mind that issues related to re-entrant behavior, resource management, and proper DLL design should still be taken into account.

In most cases, it's recommended to design your code in a way that you load the DLL once and manage the functions and data structures within your program to avoid unnecessary complications. If you have control over the DLL's source code, you can also consider making it thread-safe and re-entrant if needed.