TurboGears includes a scheduler that is based on Kronos by Irmen de Jong. This scheduler makes it easy to have one time or recurring tasks run as needed.
You can schedule Python functions to be called at specific intervals or days. It uses the standard sched module for the actual task scheduling, but provides much more:
To use the scheduler, set the tg.scheduler config variable to True in your [global] configuration. This tells TurboGears to start the scheduler when the server starts.
# Set to True if the scheduler should be started tg.scheduler = True
There are three functions in the turbogears.schedule module you can use to schedule jobs. They are called add_interval_task, add_weekday_task, and add_monthday_task.
All three functions return a Task object. If you hold on to that Task object, you can later cancel it by calling turbogears.scheduler.cancel() with that Task.
Here is an example that runs the function "do_something" every ten seconds:
from turbogears import scheduler def do_something(): print "Hello world." scheduler.add_interval_task(action=do_something, taskname='do_something', initialdelay=0, interval=10)
All three scheduling functions take the following arguments:
By default, each task will be run in a new thread. You can also pass in turbogears.scheduler.method.sequential or turbogears.scheduler.method.forked. The default is turbogears.scheduler.method.threaded.
Sequential means that the task will run in the same thread as the scheduler, and task will be execuetd sequentially, one after another. This should only be used for quick tasks.
Forked means to fork a new process to run the job, which is sometimes more effective for intense jobs, particularly on multiprocessor machines (due to Python’s architecture).
it is impossible to add new tasks to a ForkedScheduler, after the scheduler has been started!
Here’s an example of how to schedule the same function as above as a task using the sequential method:
turbogears.scheduler.add_interval_task( processmethod=turbogears.scheduler.method.sequential, action=do_something, taskname='do_something', initialdelay=5, interval=60)
In addition to these common parameters, the three scheduling functions each offer additional options to determine when they run. Here are the four functions and their parameters for how often to run:
Pass in initialdelay with a number of seconds to wait before running and an interval with the number of seconds between runs.
For example, an initialdelay of 600 and interval of 60 would mean “start running after 10 minutes and run every 1 minute after that”.
For more control you can create one of the following Task sub-classes:
All Task sub-classes support the following methods:
You can the schedule a task using one of the following methods of a Scheduler instance. To get and instance, you can either call turbogears.schedule._get_scheduler() or create your own instance of one of the following Schedule classes:
You might want to use the scheduler as a kind of mini-cron to execute tasks at regular intervals or to dynamically schedule new tasks during runtime (e.g, a RSS reader). Where you place the code for your tasks and scheduling them will depend on your application. In any case you will need to run a function to (re) schedule your tasks after application startup.
For example, you could use the scheduler to regularly run jobs ranging from reporting to updating the database using external data. For this purpose, you might create a jobs.py file in your applications package, containing a function per ‘job’ and schedule() function to schedule the tasks during startup. jobs.py basically reads as follows:
# jobs.py import datetime from turbogears.scheduler import add_weekday_task, add_interval_task def generate_product_ranking(): # do something useful here... pass def synchronize_stock(from=None): # do something useful here... pass def schedule(): add_weekday_task(action=generate_product_ranking, weekdays=range(1,8), timeonday=(0)) add_interval_task(action=synchronize_stock, args=[lambda:datetime.datetime.now() - datetime.timedelta(minutes=2)], interval=120)
Then add two lines to the start() function in commands.py, just before the TurboGears server is started, to run the schedule function at each startup (assuming your applications package is called yourpkg):
# commands.py ... def start(): ... # following two lines added from yourpkg import jobs turbogears.startup.call_on_startup.append(jobs.schedule) from yourpkg.controllers import Root turbogears.start_server(Root())
As another example, you can use the scheduler to delete expired entries in the identity tables. The following assumes you’re using SQLAlchemy and a PostgreSQL database, but you can easily adapt this to your database configuration:
# jobs.py from sqlalchemy import sql from turbogears import config from turbogears.scheduler import add_interval_task from yourpkg.model import visits_table, visit_identity_table import logging log = logging.getLogger("yourpkg.jobs") _expired_visits = sql.text("expiry<current_timestamp-'15min'::interval") _orphaned_identities = sql.text("not exists(select * from visit" " where visit_key=visit_identity.visit_key)") def delete_expired_visits(): """Delete expired visits from database.""" log.info("Deleting expired visits from database...") visits_table.delete(_expired_visits).execute() visit_identity_table.delete(_orphaned_identities).execute() def schedule(): if config.get('tg.scheduler'): log.info("Scheduling background jobs...") add_interval_task(action=delete_expired_visits, interval=30*60) else: log.warning("Scheduler not activated!")