Re: Seeking ideas for a cron implementation
On Aug 22, 1:51 pm, Sean DiZazzo [EMAIL PROTECTED] wrote: On Aug 22, 1:30 pm, Karthik Gurusamy [EMAIL PROTECTED] wrote: Hi, I'm working on acronlike functionality for my application. The outer loops runs continuously waking every x seconds (say x=180, 300, ..). It needs to know what events incronhas expired and for each event do the work needed. It's basically like unixcronor like a calendar application with some restrictions. The outer loop may come back a lot later and many events might have missed their schedule -- but this is okay.. We don't have to worry about missed events (if there were n misses, we just need to execute call back once). Let's take some examples [Let e denotes an event] e1: hour=1 min=30 # Run every day once at 1:30 AM e2: wday=0, hour=1 min=0 # run every Monday at 1 AM e3: month=10, day=10, hour=10 min=0 # run on October 10th, 10 AM every year class Cron_Event (object): def __init__ (year=None, month=None, day=None, hour=None ..etc) # do init classCron(object): def __init__ (): # do init def event_add (e): # add an event def execute() # see if any events has expired .. call it's callback # I'm looking for ideas on how to manage the events here From outer loop cron=Cron() # create various events like e1 = Cron_Event(hour=1) cron.event_add(e1) e2 = Cron_Event(wday=0, hour=1) cron.event_add(e2) while True: sleep x seconds (or wait until woken up) cron.execute() # do other work.. x may change here If I can restrict to hour and minute, it seems manageable as the interval between two occurrences is a constant. But allowing days like every Monday or 1st of every month makes things complicated. Moreover I would like each constraint in e to take on multiple possibilities (like every day at 1AM, 2 AM and 4 AM do this). I'm looking for solutions that can leverage datetime.datetime routines. My current ideas include for each e, track the next time it will fire (in seconds since epoch as given by time.time()). Once current time has passed that time, we execute the event. e.g. datetime.datetime.now() datetime.datetime(2008, 8, 22, 13, 19, 54, 5567) time.time() 1219436401.741966 --- compute event's next firing in a format like this The problem seems to be how to compute that future point in time (in seconds since epoch) for a generic Cron_Event. Say how do I know the exact time in future that will satisfy a constraint like: month=11, wday=1, hour=3, min=30 # At 3:30 AM on a Tuesday in November Thanks for your thoughts. Karthik I only scanned your message, but maybe datetime.timedelta() will help.. import datetime now = datetime.datetime.now() print now 2008-08-22 13:48:49.335225 day = datetime.timedelta(1) print day 1 day, 0:00:00 print now + day 2008-08-23 13:48:49.335225 Thanks, I found using a more efficient algorithm tricky and seemed error prone. [I do welcome ideas still if anyone has a cool solution] I used your idea and took the easy way out by using a brute-force search. Here is an outline if anyone faces similar problem: hours, minutes are lists: say for every day at 1:30 pm and 2:45 pm, hours=[13, 14] and minutes=[30, 45,]. I restricted myself to minutes and hours (and every day) to simplify the problem. def set_expiry_time_check_in_a_day (self, now, target, hours, mins, flags=set()): A small utility routine to simulate 'goto' Looks like now could be computed inside this function -- the small drift due to time taken in this function should be negligible # let's see if in today we can find an expiry # we do brute force search starting with the smallest hour for hour in hours: for min in mins: target = target.replace(hour=hour, minute=min, second=0, microsecond=0) if 'is_debug_1' in flags: print Trying target time: %s... % target if target now: if 'is_debug_1' in flags: print Found target time: %s % (target, ) return target # simulates a break from two loops return None def set_expiry_time (self, event, flags=set()): For a given event, compute and remember when it will fire next now = datetime.datetime.now() target = now # start checking from now.. # assumption, hours and mins are atleast one int element array # and they are in sorted order hours = event.spec['hours'] mins = event.spec['minutes'] tries = 0 while True: # runs of each day.. tomorrow ... tries += 1 if tries 50: #
Seeking ideas for a cron implementation
Hi, I'm working on a cron like functionality for my application. The outer loops runs continuously waking every x seconds (say x=180, 300, ..). It needs to know what events in cron has expired and for each event do the work needed. It's basically like unix cron or like a calendar application with some restrictions. The outer loop may come back a lot later and many events might have missed their schedule -- but this is okay.. We don't have to worry about missed events (if there were n misses, we just need to execute call back once). Let's take some examples [Let e denotes an event] e1: hour=1 min=30 # Run every day once at 1:30 AM e2: wday=0, hour=1 min=0 # run every Monday at 1 AM e3: month=10, day=10, hour=10 min=0 # run on October 10th, 10 AM every year class Cron_Event (object): def __init__ (year=None, month=None, day=None, hour=None ..etc) # do init class Cron (object): def __init__ (): # do init def event_add (e): # add an event def execute() # see if any events has expired .. call it's callback # I'm looking for ideas on how to manage the events here From outer loop cron = Cron() # create various events like e1 = Cron_Event(hour=1) cron.event_add(e1) e2 = Cron_Event(wday=0, hour=1) cron.event_add(e2) while True: sleep x seconds (or wait until woken up) cron.execute() # do other work.. x may change here If I can restrict to hour and minute, it seems manageable as the interval between two occurrences is a constant. But allowing days like every Monday or 1st of every month makes things complicated. Moreover I would like each constraint in e to take on multiple possibilities (like every day at 1AM, 2 AM and 4 AM do this). I'm looking for solutions that can leverage datetime.datetime routines. My current ideas include for each e, track the next time it will fire (in seconds since epoch as given by time.time()). Once current time has passed that time, we execute the event. e.g. datetime.datetime.now() datetime.datetime(2008, 8, 22, 13, 19, 54, 5567) time.time() 1219436401.741966--- compute event's next firing in a format like this The problem seems to be how to compute that future point in time (in seconds since epoch) for a generic Cron_Event. Say how do I know the exact time in future that will satisfy a constraint like: month=11, wday=1, hour=3, min=30# At 3:30 AM on a Tuesday in November Thanks for your thoughts. Karthik -- http://mail.python.org/mailman/listinfo/python-list
Re: Seeking ideas for a cron implementation
On Aug 22, 1:30 pm, Karthik Gurusamy [EMAIL PROTECTED] wrote: Hi, I'm working on a cron like functionality for my application. The outer loops runs continuously waking every x seconds (say x=180, 300, ..). It needs to know what events in cron has expired and for each event do the work needed. It's basically like unix cron or like a calendar application with some restrictions. The outer loop may come back a lot later and many events might have missed their schedule -- but this is okay.. We don't have to worry about missed events (if there were n misses, we just need to execute call back once). Let's take some examples [Let e denotes an event] e1: hour=1 min=30 # Run every day once at 1:30 AM e2: wday=0, hour=1 min=0 # run every Monday at 1 AM e3: month=10, day=10, hour=10 min=0 # run on October 10th, 10 AM every year class Cron_Event (object): def __init__ (year=None, month=None, day=None, hour=None ..etc) # do init class Cron (object): def __init__ (): # do init def event_add (e): # add an event def execute() # see if any events has expired .. call it's callback # I'm looking for ideas on how to manage the events here From outer loop cron = Cron() # create various events like e1 = Cron_Event(hour=1) cron.event_add(e1) e2 = Cron_Event(wday=0, hour=1) cron.event_add(e2) while True: sleep x seconds (or wait until woken up) cron.execute() # do other work.. x may change here If I can restrict to hour and minute, it seems manageable as the interval between two occurrences is a constant. But allowing days like every Monday or 1st of every month makes things complicated. Moreover I would like each constraint in e to take on multiple possibilities (like every day at 1AM, 2 AM and 4 AM do this). I'm looking for solutions that can leverage datetime.datetime routines. My current ideas include for each e, track the next time it will fire (in seconds since epoch as given by time.time()). Once current time has passed that time, we execute the event. e.g. datetime.datetime.now() datetime.datetime(2008, 8, 22, 13, 19, 54, 5567) time.time() 1219436401.741966 --- compute event's next firing in a format like this The problem seems to be how to compute that future point in time (in seconds since epoch) for a generic Cron_Event. Say how do I know the exact time in future that will satisfy a constraint like: month=11, wday=1, hour=3, min=30 # At 3:30 AM on a Tuesday in November Thanks for your thoughts. Karthik I only scanned your message, but maybe datetime.timedelta() will help.. import datetime now = datetime.datetime.now() print now 2008-08-22 13:48:49.335225 day = datetime.timedelta(1) print day 1 day, 0:00:00 print now + day 2008-08-23 13:48:49.335225 ~Sean -- http://mail.python.org/mailman/listinfo/python-list
