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authorGeorg Brandl <georg@python.org>2007-08-15 14:28:22 (GMT)
committerGeorg Brandl <georg@python.org>2007-08-15 14:28:22 (GMT)
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+
+:mod:`sched` --- Event scheduler
+================================
+
+.. module:: sched
+ :synopsis: General purpose event scheduler.
+.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
+
+
+.. % LaTeXed and enhanced from comments in file
+
+.. index:: single: event scheduling
+
+The :mod:`sched` module defines a class which implements a general purpose event
+scheduler:
+
+
+.. class:: scheduler(timefunc, delayfunc)
+
+ The :class:`scheduler` class defines a generic interface to scheduling events.
+ It needs two functions to actually deal with the "outside world" --- *timefunc*
+ should be callable without arguments, and return a number (the "time", in any
+ units whatsoever). The *delayfunc* function should be callable with one
+ argument, compatible with the output of *timefunc*, and should delay that many
+ time units. *delayfunc* will also be called with the argument ``0`` after each
+ event is run to allow other threads an opportunity to run in multi-threaded
+ applications.
+
+Example::
+
+ >>> import sched, time
+ >>> s=sched.scheduler(time.time, time.sleep)
+ >>> def print_time(): print "From print_time", time.time()
+ ...
+ >>> def print_some_times():
+ ... print time.time()
+ ... s.enter(5, 1, print_time, ())
+ ... s.enter(10, 1, print_time, ())
+ ... s.run()
+ ... print time.time()
+ ...
+ >>> print_some_times()
+ 930343690.257
+ From print_time 930343695.274
+ From print_time 930343700.273
+ 930343700.276
+
+
+.. _scheduler-objects:
+
+Scheduler Objects
+-----------------
+
+:class:`scheduler` instances have the following methods:
+
+
+.. method:: scheduler.enterabs(time, priority, action, argument)
+
+ Schedule a new event. The *time* argument should be a numeric type compatible
+ with the return value of the *timefunc* function passed to the constructor.
+ Events scheduled for the same *time* will be executed in the order of their
+ *priority*.
+
+ Executing the event means executing ``action(*argument)``. *argument* must be a
+ sequence holding the parameters for *action*.
+
+ Return value is an event which may be used for later cancellation of the event
+ (see :meth:`cancel`).
+
+
+.. method:: scheduler.enter(delay, priority, action, argument)
+
+ Schedule an event for *delay* more time units. Other then the relative time, the
+ other arguments, the effect and the return value are the same as those for
+ :meth:`enterabs`.
+
+
+.. method:: scheduler.cancel(event)
+
+ Remove the event from the queue. If *event* is not an event currently in the
+ queue, this method will raise a :exc:`RuntimeError`.
+
+
+.. method:: scheduler.empty()
+
+ Return true if the event queue is empty.
+
+
+.. method:: scheduler.run()
+
+ Run all scheduled events. This function will wait (using the :func:`delayfunc`
+ function passed to the constructor) for the next event, then execute it and so
+ on until there are no more scheduled events.
+
+ Either *action* or *delayfunc* can raise an exception. In either case, the
+ scheduler will maintain a consistent state and propagate the exception. If an
+ exception is raised by *action*, the event will not be attempted in future calls
+ to :meth:`run`.
+
+ If a sequence of events takes longer to run than the time available before the
+ next event, the scheduler will simply fall behind. No events will be dropped;
+ the calling code is responsible for canceling events which are no longer
+ pertinent.
+