bergundy · February 8, 2012 15:33 · Feb 8, 2012 · Feb 8, 2012
diff --git a/gistfile1.py b/gistfile1.py
@@ -66,7 +66,8 @@ def _schedule_next(self):
 
     @property
     def _next_timeout(self):
-        return self._trigger.get_next_fire_time(datetime.now()) - datetime.now()
+        d = datetime.now()
+        return self._trigger.get_next_fire_time(d) - d
 
 if __name__ == "__main__":
     import doctest

diff --git a/gistfile1.py b/gistfile1.py
@@ -0,0 +1,73 @@
+import re
+import itertools
+import logging
+
+from apscheduler.triggers.cron import CronTrigger
+from tornado.ioloop import IOLoop
+from datetime import datetime
+
+class CronCallback(object):
+    """Schedules the given callback to be called periodically.
+
+    The callback is called according to the schedule argument.
+
+    `start` must be called after the CronCallback is created.
+
+    If schedule is a string it should contain 7 cron fields: ('second', 'minute', 'hour', 'day', 'month', 'year', 'day_of_week').
+    If schedule is a dict it must contain at least one of the fields above.
+
+    >>> cron1 = CronCallback(lambda: logging.error('x'), dict(seconds = 1)) # logs 'x' every second
+    >>> cron2 = CronCallback(lambda: IOLoop.instance().stop(), '*/5 * * * * * *') # stops ioloop every 5 seconds
+    >>> cron1.start()
+    >>> cron2.start()
+    >>> IOLoop.instance().start()
+    """
+
+    _split_re  = re.compile("\s+")
+    _sched_seq = ('second', 'minute', 'hour', 'day', 'month', 'year', 'day_of_week')
+
+    def __init__(self, callback, schedule, io_loop=None):
+        if isinstance(schedule, basestring):
+            splitted = self._split_re.split(schedule)
+            if len(splitted) < 7:
+                raise TypeError("'schedule' argument pattern mismatch")
+
+            schedule = dict(itertools.izip(self._sched_seq, splitted))
+
+        self.callback = callback
+        self._trigger = CronTrigger(**schedule)
+        self.io_loop  = io_loop or IOLoop.instance()
+        self._running = False
+        self._timeout = None
+
+    def start(self):
+        """Starts the timer."""
+        self._running = True
+        self._schedule_next()
+
+    def stop(self):
+        """Stops the timer."""
+        self._running = False
+        if self._timeout is not None:
+            self.io_loop.remove_timeout(self._timeout)
+            self._timeout = None
+
+    def _run(self):
+        if not self._running: return
+        try:
+            self.callback()
+        except Exception:
+            logging.error("Error in cron callback", exc_info=True)
+        self._schedule_next()
+
+    def _schedule_next(self):
+        if self._running:
+            self._timeout = self.io_loop.add_timeout(self._next_timeout, self._run)
+
+    @property
+    def _next_timeout(self):
+        return self._trigger.get_next_fire_time(datetime.now()) - datetime.now()
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()