Close a resourceful thread gracefully

Question

I have the following function which is called from a function of a class. I would like to call this as a non blocking thread or daemon process. And I want it to be stopped gracefully taking care of any IO locks and DB locks (which happen inside foo()).

def worker(fnames):
    while True:
        for f in fnames:
            while(not os.path.isfile(f)):
                time.sleep(SLEEP_INTERVAL)
            while os.stat(f).st_size < 1000000:
                time.sleep(SLEEP_INTERVAL)
            file= open(f, 'rb')
            #Do Something
            foo()
            os.remove(f)

I looked in to first answer on this link and modified the code. Do I create a driver function for the above function, run the driver function from a new thread, and pass the _stop event flag from the below thread to it? Or is there a better way?

class StoppableThread(threading.Thread):
    def __init__(self, target, timeout):
        super(StoppableThread, self).__init__()
        self._target = target
        self._timeout = timeout
        self._stop = threading.Event()

    def run(self):
        while not self.stopped():
            self._stop.wait(self._timeout)  # instead of sleeping
            if self.stopped():
                continue
            self._target()

    def stop(self):
        self._stop.set()

    def stopped(self):
        return self._stop.isSet()

EDIT: I managed to think of the following solution, but I find it very nasty. Any help is appreciated:

def run(self):
    while True:
        for f in fnames:
            while not self._stop.isSet():
                while(not os.path.isfile(f)):
                    self._stop.wait(SLEEP_INTERVAL)
                    if self._stop.isSet():
                        break;
                while os.stat(f).st_size < 1000000:
                    self._stop.wait(SLEEP_INTERVAL)
                    if self._stop.isSet():
                        break;
                if self._stop.isSet():
                    continue;                            
                file= open(f, 'rb')
                #Do Something
                foo()
                os.remove(f)
            if self._stop.isSet():
                break;
        if self._stop.isSet():
            break;