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Cross Platform Example of Single Instance Checking in Python
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| import time, sys, os | |
| class SingleInstanceChecker: | |
| def __init__(self, id): | |
| if isWin(): | |
| ensure_win32api() | |
| self.mutexname = id | |
| self.lock = win32event.CreateMutex(None, False, self.mutexname) | |
| self.running = (win32api.GetLastError() == winerror.ERROR_ALREADY_EXISTS) | |
| else: | |
| ensure_fcntl() | |
| self.lock = open(f"/tmp/isnstance_{id}.lock", 'wb') | |
| try: | |
| fcntl.lockf(self.lock, fcntl.LOCK_EX | fcntl.LOCK_NB) | |
| self.running = False | |
| except IOError: | |
| self.running = True | |
| def already_running(self): | |
| return self.running | |
| def __del__(self): | |
| if self.lock: | |
| try: | |
| if isWin(): | |
| win32api.CloseHandle(self.lock) | |
| else: | |
| os.close(self.lock) | |
| except Exception as ex: | |
| pass | |
| # --------------------------------------- | |
| # Utility Functions | |
| # Dynamically load win32api on demand | |
| # Install with: pip install pywin32 | |
| win32api=winerror=win32event=None | |
| def ensure_win32api(): | |
| global win32api,winerror,win32event | |
| if win32api is None: | |
| import win32api | |
| import winerror | |
| import win32event | |
| # Dynamically load fcntl on demand (python stdlib) | |
| fcntl=None | |
| def ensure_fcntl(): | |
| global fcntl | |
| if fcntl is None: | |
| import fcntl | |
| def isWin(): | |
| return (os.name == 'nt') | |
| # --------------------------------------- | |
| def main(argv): | |
| _timeout = 10 | |
| print("main() called. sleeping for %s seconds" % _timeout) | |
| time.sleep(_timeout) | |
| print("DONE") | |
| if __name__ == '__main__': | |
| SCR_NAME = "my_script" | |
| sic = SingleInstanceChecker(SCR_NAME) | |
| if sic.already_running(): | |
| print("An instance of {} is already running.".format(SCR_NAME)) | |
| sys.exit(1) | |
| else: | |
| main(sys.argv[1:]) |
Author
@JavaScriptDude Apologies if I gave the impression the code doesn't work - it does work. My code base is typed and so wanted to type this. I'll investigate further.
Author
No problem at all. Glad to have my open source code being helpful.
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The code definitely works and I've used it in dozens of usecases where I develop the code in linux and deploy in windows in some cases. I use this code for my scheduled task / cron based jobs.