catch change in security permission of file without blocking

Question

I want to catch change in security permission of file without blocking till the change is made, like an event that popup when the change is made.

I also don't want to install any third party modules or softwares.

The main requirement of this is to be in some of win32 modules or built-in modules.

I'm currently watching for security change by this function:

    import win32con, win32file
    def security_watcher():

        specific_file = "specific.ini"
        path_to_watch = "." 
        FILE_LIST_DIRECTORY = 0x0001
        hDir = win32file.CreateFile(path_to_watch,
                                    FILE_LIST_DIRECTORY,
                                    win32con.FILE_SHARE_READ | 
                                    win32con.FILE_SHARE_WRITE | 
                                    win32con.FILE_SHARE_DELETE,
                                    None,
                                    win32con.OPEN_EXISTING,
                                    win32con.FILE_FLAG_BACKUP_SEMANTICS,
                                    None)
        results = win32file.ReadDirectoryChangesW(hDir,
                                                  1024,
                                                  False,
                                                  win32con.FILE_NOTIFY_CHANGE_SECURITY,
                                                  None,
                                                  None)
        print results
        for action, file_name in results:
            if file_name == specific_file:
               # wake another function to do something about that

Note: I need it non blocking because I use this function in GUI Application and it freezes the GUI.

Answer 1

If you don't mind (or can't avoid) adding some threading overhead, you can launch a separate process or thread that waits on the blocking call to win32.ReadDirectoryChangesW() that you already have. When it receives a change, it writes the result to a pipe shared with the main thread of your GUI.

Your GUI can periodically execute a non-blocking read at the appropriate point in your code (presumably, where you now call win32file.ReadDirectoryChangesW()). Do make sure to wait a bit between reads, or your app will spend 100% of its time on non-blocking reads.

You can see in this answer how to set up a non-blocking read on a pipe in an OS-independent way. The final bit will look like this:

try:  
    results = q.get_nowait()
except Empty:
    pass
else:  
    for line in results.splitlines():
        # Parse and use your result format
        ...
        if file_name == specific_file:
            ...