I'm writing a Python application that connects to an external device. I want to enable the user to operate multiple devices simultaneously by running multiple instances of the application, but each device may only connect to one application instance. This calls for a mutex keyed to the device's serial number. With the help of ChatGPT, I came up with the following minimal example (without the serial number): import ctypes import sys ERROR_ALREADY_EXISTS = 183 mutex = ctypes.windll.kernel32.CreateMutexW(None, 1, "my-app\\1234") err = ctypes.GetLastError() print(f'Error code received: {err}') if err == ERROR_ALREADY_EXISTS: print("Another instance is already using the device.") sys.exit(0) input("Program running. Press Enter to exit...") When I open two command windows and run this script in each one, neither one errors out and both give an err value of 3. I checked the Microsoft documentation for CreateMutexW and for the error codes, and I can't figure out what I'm doing wrong. Continue reading...
