Threaded file watcher

daemon.py

import os
import signal
import sys
import time
import threading

class Daemon(object):
    """A simple class to properly daemonize a process"""

    def __init__(self):
        self.running = True
    
    def daemonize(self):
        signal.signal(signal.SIGTERM, self._terminate)
        signal.signal(signal.SIGQUIT, self._terminate)
        """ do other daemonize steps (i.e. chdir('/'), setsid(), double-fork, close files, etc.) """
        
    def _terminate(self):
        self.running = False
        
    def run(self):
        raise (RuntimeError, 'please implement run() in subclass')
    
class ProcessorDaemon(Daemon):
    def run(self):
        self.follower = FollowerThread()
        self.non_follower = NonFollowerThread()
        
        self.follower.start()
        self.non_follower.start()
        
        while self.running:
            time.sleep(1)
            
        self.follower.stop()
        self.non_follower.stop()
        
        self.follower.join()
        self.non_follower.join()
        

class DaemonThread(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self._finished = threading.Event()
        
        
class NonFollowerThread(DaemonThread):
    def run(self):
        for line in open('file_to_watch.log'):
            if self._finished.is_set():
                return
            process_line()
            

class FollowerThread(DaemonThread):
    def run(self):
        loglines = follow(open('file_to_watch.log'))
        for line in loglines:
            if self._finished.is_set():
                return
            process_line()
            
            
def follow(target):
    """stolen/modified from @dabeaz: http://www.dabeaz.com/generators/follow.py"""
    target.seek(0, 2)
    while True:
        line = ''
        while len(line) == 0 or line[-1] != '\n':
            tail = target.readline()
            if tail == '':
                time.sleep(0.1)
                continue
            line += tail
        yield line
    
    
if __name__ == '__main__':
    daemon = ProcessorDaemon()
    daemon.daemonize()
    daemon.run()